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  • 1. Adachi, Kouji
    et al.
    Tobo, Yutaka
    Koike, Makoto
    Pereira Freitas, Gabriel
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Composition and mixing state of Arctic aerosol and cloud residual particles from long-term sinale-particle observations at Zeppelin Observatory, Svalbard2022In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 22, no 21, p. 14421-14439Article in journal (Refereed)
    Abstract [en]

    The Arctic region is sensitive to climate change and is warming faster than the global average. Aerosol particles change cloud properties by acting as cloud condensation nuclei and ice-nucleating particles, thus influencing the Arctic climate system. Therefore, understanding the aerosol particle properties in the Arctic is needed to interpret and simulate their influences on climate. In this study, we collected ambient aerosol particles using whole-air and PM10 inlets and residual particles of cloud droplets and ice crystals from Arctic low-level clouds (typically, all-liquid or mixed-phase clouds) using a counterflow virtual impactor inlet at the Zeppelin Observatory near Ny-Ålesund, Svalbard, within a time frame of 4 years. We measured the composition and mixing state of individual fine-mode particles in 239 samples using transmission electron microscopy. On the basis of their composition, the aerosol and cloud residual particles were classified as mineral dust, sea salt, K-bearing, sulfate, and carbonaceous particles. The number fraction of aerosol particles showed seasonal changes, with sulfate dominating in summer and sea salt increasing in winter. There was no measurable difference in the fractions between ambient aerosol and cloud residual particles collected at ambient temperatures above 0 C. On the other hand, cloud residual samples collected at ambient temperatures below 0 C had several times more sea salt and mineral dust particles and fewer sulfates than ambient aerosol samples, suggesting that sea spray and mineral dust particles may influence the formation of cloud particles in Arctic mixed-phase clouds. We also found that 43 % of mineral dust particles from cloud residual samples were mixed with sea salt, whereas only 18 % of mineral dust particles in ambient aerosol samples were mixed with sea salt. This study highlights the variety in aerosol compositions and mixing states that influence or are influenced by aerosol–cloud interactions in Arctic low-level clouds.

  • 2. Adachi, Kouji
    et al.
    Tobo, Yutaka
    Oshima, Naga
    Yoshida, Atsushi
    Ohata, Sho
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, Department of Meteorology . Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Massling, Andreas
    Skov, Henrik
    Koike, Makoto
    Composition and mixing state of individual aerosol particles from northeast Greenland and Svalbard in the Arctic during spring 20182023In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 314, article id 120083Article in journal (Refereed)
    Abstract [en]

    The Arctic region is warming about four times faster than the rest of the globe, and thus it is important to understand the processes driving climate change in this region. Aerosols are a significant component of the Arctic climate system as they form ice crystals and liquid droplets that control the dynamics of clouds and also directly interact with solar radiation, depending on the compositions and mixing states of individual particles. Here, we report on the characteristics of submicron-sized aerosol particles using transmission electron microscopy obtained at two high Arctic sites, northeast Greenland (Villum Research Station) and Svalbard (Zeppelin Observatory), during spring 2018. The results showed that a dominant compound in the submicron-sized spring aerosols was sulfate, followed by sea salt particles. Both model simulations and observations at the Zeppelin Observatory showed that sea salt particles became more prevalent when low-pressure systems passed by the station. Model simulations indicate that both sampling sites were affected by diffused and diluted long-range transport of anthropogenic aerosols from lower latitudes with negligible influences of biomass burning emissions during the observation period. Overall, the composition of measured aerosol particles from the two Arctic sites was generally similar and showed no apparent variation except for the sea salt fractions. This study shows a general picture of high Arctic aerosol particles influenced by marine sources and diffused long-range transport of anthropogenic sources during the Arctic spring period. These results will contribute to a better knowledge of the aerosol composition and mixing state during the Arctic spring, which helps to understand the contributions of aerosols to the Arctic climate.

  • 3.
    Ahlm, L
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Nilsson, D
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, R
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mårtensson, M
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Vogt, M
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Artaxo, P.
    Aerosol Fluxes over Amazon Rain Forest Measured with the Eddy Covariance Method2008In: American Geophysical Union (AGU) Fall Meeting 2008: 15-19 December, San Fransisco, CA, USA, 2008Conference paper (Refereed)
  • 4.
    Ahlm, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Nilsson, Douglas
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mårtensson, Monica
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Vogt, Matthias
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Artaxo, Paulo
    Emission and dry deposition of accumulation mode particles in the Amazon Basin2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 21, p. 10237-10253Article in journal (Refereed)
    Abstract [en]

    Size-resolved vertical aerosol number fluxes of particles in the diameter range 0.25–2.5 μm were measured with the eddy covariance method from a 53 m high tower over the Amazon rain forest, 60 km NNW of Manaus, Brazil. This study focuses on data measured during the relatively clean wet season, but a shorter measurement period from the more polluted dry season is used as a comparison. Size-resolved net particle fluxes of the five lowest size bins, representing 0.25–0.45 μm in diameter, pointed downward in more or less all wind sectors in the wet season. This is an indication that the source of primary biogenic aerosol particles may be small in this particle size range. In the diameter range 0.5–2.5 μm, vertical particle fluxes were highly dependent on wind direction. In wind sectors where anthropogenic influence was low, net emission fluxes dominated. However, in wind sectors associated with higher anthropogenic influence, net deposition fluxes dominated. The net emission fluxes were interpreted as primary biogenic aerosol emission, but deposition of anthropogenic particles seems to have masked this emission in wind sectors with higher anthropogenic influence. The emission fluxes were at maximum in the afternoon when the mixed layer is well developed, and these emissions were best correlated with horizontal wind speed by the equation log10F=0.47·U+2.26 where F is the emission number flux of 0.5–2.5 μm particles [m−2s−1] and U is the horizontal wind speed [ms−1] at the top of the tower.

  • 5.
    Ahlm, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Nilsson, Douglas
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mårtensson, Monica
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Vogt, Matthias
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Artaxo, Paulo
    Size-resolved dry deposition velocities of particles with diameters 0.25-0.45 μm to a tropical rain forestManuscript (preprint) (Other academic)
  • 6.
    Ahlm, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Nilsson, Douglas
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mårtensson, Monica
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Vogt, Matthias
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Artaxo, Paulo
    A comparison of dry and wet season aerosol number fluxes over the Amazon rain forest2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 6, p. 3063-3079Article in journal (Refereed)
    Abstract [en]

    Vertical number fluxes of aerosol particles and vertical fluxes of CO2 were measured with the eddy covariance method at the top of a 53m high tower in the Amazon rain forest as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) experiment. The observed aerosol number fluxes included particles with sizes down to 10 nm in diameter. The measurements were carried out during the wet and dry season in 2008. In this study focus is on the dry season aerosol fluxes, with significant influence from biomass burning, and these are compared with aerosol fluxes measured during the wet season. Net particle deposition fluxes dominated in daytime in both seasons and the deposition flux was considerably larger in the dry season due to the much higher dry season particle concentration. The particle transfer velocity increased linearly with increasing friction velocity in both seasons. The difference in transfer velocity between the two seasons was small, indicating that the seasonal change in aerosol number size distribution is not enough for causing any significant change in deposition velocity. In general, particle transfer velocities in this study are low compared to studies over boreal forests. The reasons are probably the high percentage of accumulation mode particles and the low percentage of nucleation mode particles in the Amazon boundary layer, both in the dry and wet season, and low wind speeds in the tropics compared to the midlatitudes. In the dry season, nocturnal particle fluxes behaved very similar to the nocturnal CO2 fluxes. Throughout the night, the measured particle flux at the top of the tower was close to zero, but early in the morning there was an upward particle flux peak that is not likely a result of entrainment or local pollution. It is possible that these morning upward particle fluxes are associated with emission of primary biogenic particles from the rain forest. Emitted particles may be stored within the canopy during stable conditions at nighttime, similarly to CO2, and being released from the canopy when conditions become more turbulent in the morning.

  • 7.
    Ahlm, Lars
    et al.
    Stockholm University, Faculty of Science. Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Nilsson, Douglas
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mårtensson, Monica
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Vogt, Matthias
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Artaxo, Paulo
    Aerosol number fluxes over the Amazon rain forest during the wet season2009In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 9, no 24, p. 9381-9400Article in journal (Refereed)
    Abstract [en]

    Number fluxes of particles with diameter larger than 10 nm were measured with the eddy covariance method over the Amazon rain forest during the wet season as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) campaign 2008. The primary goal was to investigate whether sources or sinks dominate the aerosol number flux in the tropical rain forest-atmosphere system. During the measurement campaign, from 12 March to 18 May, 60% of the particle fluxes pointed downward, which is a similar fraction to what has been observed over boreal forests. The net deposition flux prevailed even in the absolute cleanest atmospheric conditions during the campaign and therefore cannot be explained only by deposition of anthropogenic particles. The particle transfer velocity vt increased with increasing friction velocity and the relation is described by the equation vt=2.4×10−3×u* where u* is the friction velocity. Upward particle fluxes often appeared in the morning hours and seem to a large extent to be an effect of entrainment fluxes into a growing mixed layer rather than primary aerosol emission. In general, the number source of primary aerosol particles within the footprint area of the measurements was small, possibly because the measured particle number fluxes reflect mostly particles less than approximately 200 nm. This is an indication that the contribution of primary biogenic aerosol particles to the aerosol population in the Amazon boundary layer may be low in terms of number concentrations. However, the possibility of horizontal variations in primary aerosol emission over the Amazon rain forest cannot be ruled out.

  • 8. Ahn, Seo H.
    et al.
    Yoon, Y. J.
    Choi, T. J.
    Lee, J. Y.
    Kim, Y. P.
    Lee, B. Y.
    Ritter, C.
    Aas, W.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Jung, Chang H.
    Relationship between cloud condensation nuclei (CCN) concentration and aerosol optical depth in the Arctic region2021In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 267, article id 118748Article in journal (Refereed)
    Abstract [en]

    To determine the direct and indirect effects of aerosols on climate, it is important to know the spatial and temporal variations in cloud condensation nuclei (CCN) concentrations. Although many types of CCN measurements are available, extensive CCN measurements are challenging because of the complexity and high operating cost, especially in remote areas. As aerosol optical depth (AOD) can be readily observed by remote sensing, many attempts have been made to estimate CCN concentrations from AOD. In this study, the CCN-AOD relationship is parameterized based on CCN ground measurements from the Zeppelin Observatory (78.91 degrees N, 11.89 degrees E, 474 m asl) in the Arctic region. The AOD measurements were obtained from the Ny-Alesund site (78.923 degrees N, 11.928 degrees E) and Modern-Era Retrospective Analysis for Research and Applications, Version 2 reanalysis. Our results show a CCN-AOD correlation with a coefficient of determination R-2 of 0.59. Three additional estimation models for CCN were presented based on the following data: (i) in situ aerosol chemical composition, (ii) in situ aerosol optical properties, and (iii) chemical composition of AOD obtained from reanalysis data. The results from the model using in situ aerosol optical properties reproduced the observed CCN concentration most efficiently, suggesting that the contribution of BC to CCN concentration should be considered along with that of sulfate.

  • 9. Aliaga, Diego
    et al.
    Sinclair, Victoria A.
    Andrade, Marcos
    Artaxo, Paulo
    Carbone, Samara
    Kadantsev, Evgeny
    Laj, Paolo
    Wiedensohler, Alfred
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Bianchi, Federico
    Identifying source regions of air masses sampled at the tropical high-altitude site of Chacaltaya using WRF-FLEXPART and cluster analysis2021In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 21, no 21, p. 16453-16477Article in journal (Refereed)
    Abstract [en]

    Observations of aerosol and trace gases in the remote troposphere are vital to quantify background concentrations and identify long-term trends in atmospheric composition on large spatial scales. Measurements made at high altitude are often used to study free-tropospheric air; however such high-altitude sites can be influenced by boundary layer air masses. Thus, accurate information on air mass origin and transport pathways to high-altitude sites is required. Here we present a new method, based on the source-receptor relationship (SRR) obtained from backwards WRF-FLEXPART simulations and a k-means clustering approach, to identify source regions of air masses arriving at measurement sites. Our method is tailored to areas of complex terrain and to stations influenced by both local and long-range sources. We have applied this method to the Chacaltaya (CHC) GAW station (5240 m a.s.l.; 16.35 degrees S, 68.13 degrees W) for the 6-month duration of the Southern Hemisphere high-altitude experiment on particle nucleation and growth (SALILNA) to identify where sampled air masses originate and to quantify the influence of the surface and the free troposphere. A key aspect of our method is that it is probabilistic, and for each observation time, more than one air mass (cluster) can influence the station, and the percentage influence of each air mass can be quantified. This is in contrast to binary methods, which label each observation time as influenced by either boundary layer or free-troposphere air masses. Air sampled at CHC is a mix of different provenance. We find that on average 9 % of the air, at any given observation time, has been in contact with the surface within 4 d prior to arriving at CHC. Furthermore, 24 % of the air has been located within the first 1.5 km above ground level (surface included). Consequently, 76 % of the air sampled at CHC originates from the free troposphere. However, pure free-tropospheric influences are rare, and often samples are concurrently influenced by both boundary layer and free-tropospheric air masses. A clear diurnal cycle is present, with very few air masses that have been in contact with the surface being detected at night. The 6-month analysis also shows that the most dominant air mass (cluster) originates in the Amazon and is responsible for 29 % of the sampled air. Furthermore, short-range clusters (origins within 100 km of CHC) have high temporal frequency modulated by local meteorology driven by the diurnal cycle, whereas the mid- and long-range clusters' (> 200 km) variability occurs on timescales governed by synoptic-scale dynamics. To verify the reliability of our method, in situ sulfate observations from CHC are combined with the SRR clusters to correctly identify the (pre-known) source of the sulfate: the Sabancaya volcano located 400 km north-west from the station.

  • 10. Allen, G.
    et al.
    Coe, H.
    Clarke, A.
    Bretherton, C.
    Wood, R.
    Abel, S. J.
    Barrett, P.
    Brown, P.
    George, R.
    Freitag, S.
    McNaughton, C.
    Howell, S.
    Shank, L.
    Kapustin, V.
    Brekhovskikh, V.
    Kleinman, L.
    Lee, Y-N
    Springston, S.
    Toniazzo, T.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Fochesatto, J.
    Shaw, G.
    Krecl, P.
    Brooks, B.
    McMeeking, G.
    Bower, K. N.
    Williams, P. I.
    Crosier, J.
    Crawford, I.
    Connolly, P.
    Allan, J. D.
    Covert, D.
    Bandy, A. R.
    Russell, L. M.
    Trembath, J.
    Bart, M.
    McQuaid, J. B.
    Wang, J.
    Chand, D.
    South East Pacific atmospheric composition and variability sampled = ong 20 degrees S during VOCALS-REx2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 11, p. 5237-5262Article in journal (Refereed)
    Abstract [en]

    The VAMOS Ocean-Cloud-Atmosphere-Land Regional Experiment (VOCALS-REx) was conducted from 15 October to 15 November 2008 in the South East Pacific (SEP) region to investigate interactions between land, sea and atmosphere in this unique tropical eastern ocean environment and to improve the skill of global and regional models in = presenting the region. This study synthesises selected aircraft, ship = d surface site observations from VOCALS-REx to statistically summarise = d characterise the atmospheric composition and variability of the = rine Boundary Layer (MBL) and Free Troposphere (FT) along the 20 = grees S parallel between 70 degrees W and 85 degrees W. Significant = nal gradients in mean MBL sub-micron aerosol particle size and = mposition, carbon monoxide, sulphur dioxide and ozone were seen over = e campaign, with a generally more variable and polluted coastal = vironment and a less variable, more pristine remote maritime regime. = adients in aerosol and trace gas concentrations were observed to be = sociated with strong gradients in cloud droplet number. The FT was = ten more polluted in terms of trace gases than the MBL in the mean; = wever increased variability in the FT composition suggests an episodic = ture to elevated concentrations. This is consistent with a complex = rtical interleaving of airmasses with diverse sources and hence = llutant concentrations as seen by generalised back trajectory = alysis, which suggests contributions from both local and long-range = urces. Furthermore, back trajectory analysis demonstrates that the = served zonal gradients both in the boundary layer and the free = oposphere are characteristic of marked changes in airmass history with = stance offshore - coastal boundary layer airmasses having been in = cent contact with the local land surface and remote maritime airmasses = ving resided over ocean for in excess of ten days. Boundary layer = mposition to the east of 75 degrees W was observed to be dominated by = astal emissions from sources to the west of the Andes, with evidence = r diurnal pumping of the Andean boundary layer above the height of the = rine capping inversion. Analysis of intra-campaign variability in = mospheric composition was not found to be significantly correlated = th observed low-frequency variability in the large scale flow pattern; = mpaign-average interquartile ranges of CO, SO(2) and O(3) = ncentrations at all longitudes were observed to dominate over much = aller differences in median concentrations calculated between periods = different flow regimes. The campaign climatology presented here aims = provide a valuable dataset to inform model simulation and future = ocess studies, particularly in the context of aerosol-cloud = teraction and further evaluation of dynamical processes in the SEP = gion for conditions analogous to those during VOCALS-REx. To this end, = r results are discussed in terms of coastal, transitional and remote = atial regimes in the MBL and FT and a gridded dataset are provided as = resource.

  • 11. Artaxo, Paulo
    et al.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Andreae, Meinrat O.
    Bäck, Jaana
    Alves, Eliane Gomes
    Barbosa, Henrique M. J.
    Bender, Frida
    Stockholm University, Faculty of Science, Department of Meteorology .
    Bourtsoukidis, Efstratios
    Carbone, Samara
    Chi, Jinshu
    Decesari, Stefano
    Després, Viviane R.
    Ditas, Florian
    Ezhova, Ekaterina
    Fuzzi, Sandro
    Hasselquist, Niles J.
    Heintzenberg, Jost
    Holanda, Bruna A.
    Guenther, Alex
    Hakola, Hannele
    Heikkinen, Liine
    Kerminen, Veli-Matti
    Kontkanen, Jenni
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Kulmala, Markku
    Lavric, Jost V.
    de Leeuw, Gerrit
    Lehtipalo, Katrianne
    Machado, Luiz Augusto T.
    McFiggans, Gordon
    Franco, Marco Aurelio M.
    Meller, Bruno Backes
    Morais, Fernando G.
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Morgan, William
    Nilsson, Mats B.
    Peichl, Matthias
    Petäjä, Tuukka
    Praß, Maria
    Pöhlker, Christopher
    Pöhlker, Mira L.
    Pöschl, Ulrich
    Von Randow, Celso
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Rinne, Janne
    Rizzo, Luciana
    Rosenfeld, Daniel
    Silva Dias, Maria A. F.
    Sogacheva, Larisa
    Stier, Philip
    Swietlicki, Erik
    Sörgel, Matthias
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Virkkula, Aki
    Wang, Jian
    Weber, Bettina
    Maria Yáñez-Serrano, Ana
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Mikhailov, Eugene
    Smith, James N.
    Kesselmeier, Jürgen
    Tropical and Boreal Forest – Atmosphere Interactions: A Review2022In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 74, no 1, p. 24-163Article, review/survey (Refereed)
    Abstract [en]

    This review presents how the boreal and the tropical forests affect the atmosphere, its chemical composition, its function, and further how that affects the climate and, in return, the ecosystems through feedback processes. Observations from key tower sites standing out due to their long-term comprehensive observations: The Amazon Tall Tower Observatory in Central Amazonia, the Zotino Tall Tower Observatory in Siberia, and the Station to Measure Ecosystem-Atmosphere Relations at Hyytiäla in Finland. The review is complemented by short-term observations from networks and large experiments.

    The review discusses atmospheric chemistry observations, aerosol formation and processing, physiochemical aerosol, and cloud condensation nuclei properties and finds surprising similarities and important differences in the two ecosystems. The aerosol concentrations and chemistry are similar, particularly concerning the main chemical components, both dominated by an organic fraction, while the boreal ecosystem has generally higher concentrations of inorganics, due to higher influence of long-range transported air pollution. The emissions of biogenic volatile organic compounds are dominated by isoprene and monoterpene in the tropical and boreal regions, respectively, being the main precursors of the organic aerosol fraction.

    Observations and modeling studies show that climate change and deforestation affect the ecosystems such that the carbon and hydrological cycles in Amazonia are changing to carbon neutrality and affect precipitation downwind. In Africa, the tropical forests are so far maintaining their carbon sink.

    It is urgent to better understand the interaction between these major ecosystems, the atmosphere, and climate, which calls for more observation sites, providing long-term data on water, carbon, and other biogeochemical cycles. This is essential in finding a sustainable balance between forest preservation and reforestation versus a potential increase in food production and biofuels, which are critical in maintaining ecosystem services and global climate stability. Reducing global warming and deforestation is vital for tropical forests.

  • 12. Ashworth, Kirsti
    et al.
    Bucci, Silvia
    Gallimore, Peter J.
    Lee, Junghwa
    Nelson, Beth S.
    Sanchez-Marroquín, Alberto
    Schimpf, Marina B.
    Smith, Paul D.
    Drysdale, Will S.
    Hopkins, Jim R.
    Lee, James D.
    Pitt, Joe R.
    Di Carlo, Piero
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    McQuaid, James B.
    Megacity and local contributions to regional air pollution: an aircraft case study over London2020In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 20, no 12, p. 7193-7216Article in journal (Refereed)
    Abstract [en]

    In July 2017 three research flights circumnavigating the megacity of London were conducted as a part of the STANCO training school for students and early career researchers organised by EUFAR (European Facility for Airborne Research). Measurements were made from the UK's Facility for Airborne Atmospheric Measurements (FAAM) BAe-146-301 atmospheric research aircraft with the aim to sample, characterise and quantify the impact of megacity outflow pollution on air quality in the surrounding region. Conditions were extremely favourable for airborne measurements, and all three flights were able to observe clear pollution events along the flight path. A small change in wind direction provided sufficiently different air mass origins over the 2 d such that a distinct pollution plume from London, attributable marine emissions and a double-peaked dispersed area of pollution resulting from a combination of local and transported emissions were measured. We were able to analyse the effect of London emissions on air quality in the wider region and the extent to which local sources contribute to pollution events. The background air upwind of London was relatively clean during both days; concentrations of CO were 88-95 ppbv, total (measured) volatile organic compounds (VOCs) were 1.6-1.8 ppbv and NOx was 0.7-0.8 ppbv. Downwind of London, we encountered elevations in all species with CO>100 ppbv, VOCs 2.8-3.8 ppbv, CH4> 2080 ppbv and NOx >4 ppbv, and peak concentrations in individual pollution events were higher still. Levels of O-3 were inversely correlated with NOx, during the first flight, with O-3 concentrations of 37 ppbv upwind falling to similar to 26 ppbv in the well-defined London plume. Total pollutant fluxes from London were estimated through a vertical plane downwind of the city. Our calculated CO2 fluxes are within the combined uncertainty of those estimated previously, but there was a greater disparity in our estimates of CH4 and CO. On the second day, winds were lighter and downwind O-3 concentrations were elevated to similar to 39-43 ppbv (from similar to 32 to 35 ppbv upwind), reflecting the contribution of more aged pollution to the regional background. Elevations in pollutant concentrations were dispersed over a wider area than the first day, although we also encountered a number of clear transient enhancements from local sources. This series of flights demonstrated that even in a region of megacity outflow, such as the south-east of the UK, local fresh emissions and more distant UK sources of pollution can all contribute substantially to pollution events. In the highly complex atmosphere around a megacity where a high background level of pollution mixes with a variety of local sources at a range of spatial and temporal scales and atmospheric dynamics are further complicated by the urban heat island, the use of pollutant ratios to track and determine the ageing of air masses may not be valid. The individual sources must therefore all be well-characterised and constrained to understand air quality around megacities such as London. Research aircraft offer that capability through targeted sampling of specific sources and longitudinal studies monitoring trends in emission strength and profiles over time.

  • 13.
    Bardakov, Roman
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology . Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    The Role of Convective Up- and Downdrafts in the Transport of Trace Gases in the Amazon2022In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 127, no 18, article id e2022JD037265Article in journal (Refereed)
    Abstract [en]

    Deep convective clouds can redistribute gaseous species and particulate matter among different layers of the troposphere with important implications for atmospheric chemistry and climate. The large number of atmospheric trace gases of different volatility makes it challenging to predict their partitioning between hydrometeors and gas phase inside highly dynamic deep convective clouds. In this study, we use an ensemble of 51,200 trajectories simulated with a cloud-resolving model to characterize up- and downdrafts within Amazonian deep convective clouds. We also estimate the transport of a set of hypothetical non-reactive gases of different volatility, within the up- and downdrafts. We find that convective air parcels originating from the boundary layer (i.e., originating at 0.5 km altitude), can transport up to 25% of an intermediate volatility gas species (e.g., methyl hydrogen peroxide) and up to 60% of high volatility gas species (e.g., n-butane) to the cloud outflow above 10 km through the mean convective updraft. At the same time, the same type of gases can be transported to the boundary layer from the middle troposphere (i.e., originating at 5 km) within the mean convective downdraft with an efficiency close to 100%. Low volatility gases (e.g., nitric acid) are not efficiently transported, neither by the updrafts nor downdrafts, if the gas is assumed to be fully retained in a droplet upon freezing. The derived properties of the mean up- and downdraft can be used in future studies for investigating convective transport of a larger set of reactive trace gases.

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  • 14.
    Bardakov, Roman
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Vertical redistribution of air and trace gases within deep convective clouds over the Amazon: a statistical analysis based on a trajectory ensembleManuscript (preprint) (Other academic)
  • 15.
    Bardakov, Roman
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Savre, Julien
    Thornton, Joel A.
    Stockholm University, Faculty of Science, Department of Meteorology . University of Washington, USA.
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    A Novel Framework to Study Trace Gas Transport in Deep Convective Clouds2020In: Journal of Advances in Modeling Earth Systems, ISSN 1942-2466, Vol. 12, no 5, article id e2019MS001931Article in journal (Refereed)
    Abstract [en]

    Deep convective clouds reach the upper troposphere (8-15 km height). In addition to moisture and aerosol particles, they can bring aerosol precursor gases and other reactive trace gases from the planetary boundary layer to the cloud top. In this paper, we present a method to estimate trace gas transport based on the analysis of individual air parcel trajectories. Large eddy simulation of an idealized deep convective cloud was used to provide realistic environmental input to a parcel model. For a buoyant parcel, we found that the trace gas transport approximately follows one out of three scenarios, determined by a combination of the equilibrium vapor pressure (containing information about water-solubility and pure component saturation vapor pressure) and the enthalpy of vaporization. In one extreme, the trace gas will eventually be completely removed by precipitation. In the other extreme, there is almost no vapor condensation on hydrometeors and most of the gas is transported to the top of the cloud. The scenario in between these two extremes is also characterized by strong gas condensation, but a small fraction of the trace gas may still be transported aloft. This approach confirms previously suggested patterns of inert trace gas behavior in deep convective clouds, agrees with observational data, and allows estimating transport in analytically simple and computationally efficient way compared to explicit cloud-resolving model calculations.

  • 16.
    Bardakov, Roman
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Thornton, Joel A.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Transport and chemistry of isoprene and its oxidation products in deep convective clouds2021In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 73, no 1, p. 1-21Article in journal (Refereed)
    Abstract [en]

    Deep convective clouds can transport trace gases from the planetary boundary layer into the upper troposphere where subsequent chemistry may impact aerosol particle formation and growth. In this modelling study, we investigate processes that affect isoprene and its oxidation products injected into the upper troposphere by an isolated deep convective cloud in the Amazon. We run a photochemical box model with coupled cloud microphysics along hundreds of individual air parcel trajectories sampled from a cloud-resolving model simulation of a convective event. The box model simulates gas-phase chemical reactions, gas scavenging by liquid and ice hydrometeors, and turbulent dilution inside a deep convective cloud. The results illustrate the potential importance of gas uptake to anvil ice in regulating the intensity of the isoprene oxidation and associated low volatility organic vapour concentrations in the outflow. Isoprene transport and fate also depends on the abundance of lightning-generated nitrogen oxide radicals (NOx = NO + NO2). If gas uptake on ice is efficient and lightning activity is low, around 30% of the boundary layer isoprene will survive to the cloud outflow after approximately one hour of transport, while all the low volatile oxidation products will be scavenged by the cloud hydrometeors. If lightning NOx is abundant and gas uptake by ice is inefficient, then all isoprene will be oxidised during transport or in the immediate outflow region, while several low volatility isoprene oxidation products will have elevated concentrations in the cloud outflow. Reducing uncertainties associated with the uptake of vapours on ice hydrometeors, especially HO2 and oxygenated organics, is essential to improve predictions of isoprene and its oxidation products in deep convective outflows and their potential contribution to new particle formation and growth.

  • 17. Beck, Lisa J.
    et al.
    Sarnela, Nina
    Junninen, Heikki
    Hoppe, Clara J. M.
    Garmash, Olga
    Bianchi, Federico
    Riva, Matthieu
    Rose, Clemence
    Peräkylä, Otso
    Wimmer, Daniela
    Kausiala, Oskari
    Jokinen, Tuija
    Ahonen, Lauri
    Mikkilä, Jyri
    Hakala, Jani
    He, Xu-Cheng
    Kontkanen, Jenni
    Wolf, Klara K. E.
    Cappelletti, David
    Mazzola, Mauro
    Traversi, Rita
    Petroselli, Chiara
    Viola, Angelo P.
    Vitale, Vito
    Lange, Robert
    Massling, Andreas
    Nøjgaard, Jakob K.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Karlsson, Linn
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Jang, Sehyun
    Lee, Kitack
    Vakkari, Ville
    Lampilahti, Janne
    Thakur, Roseline C.
    Leino, Katri
    Kangasluoma, Juha
    Duplissy, Ella-Maria
    Siivola, Erkki
    Marbouti, Marjan
    Tham, Yee Jun
    Saiz-Lopez, Alfonso
    Petäjä, Tuukka
    Ehn, Mikael
    Worsnop, Douglas R.
    Skov, Henrik
    Kulmala, Markku
    Kerminen, Veli-Matti
    Sipilä, Mikko
    Differing Mechanisms of New Particle Formation at Two Arctic Sites2021In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 48, no 4, article id e2020GL091334Article in journal (Refereed)
    Abstract [en]

    New particle formation in the Arctic atmosphere is an important source of aerosol particles. Understanding the processes of Arctic secondary aerosol formation is crucial due to their significant impact on cloud properties and therefore Arctic amplification. We observed the molecular formation of new particles from low-volatility vapors at two Arctic sites with differing surroundings. In Svalbard, sulfuric acid (SA) and methane sulfonic acid (MSA) contribute to the formation of secondary aerosol and to some extent to cloud condensation nuclei (CCN). This occurs via ion-induced nucleation of SA and NH3 and subsequent growth by mainly SA and MSA condensation during springtime and highly oxygenated organic molecules during summertime. By contrast, in an ice-covered region around Villum, we observed new particle formation driven by iodic acid but its concentration was insufficient to grow nucleated particles to CCN sizes. Our results provide new insight about sources and precursors of Arctic secondary aerosol particles.

  • 18.
    Behrenfeldt, Ulrika
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Meteorology.
    Ström, Johan
    Department of Applied Environmental Science (ITM).
    Stohl, Andreas
    Chemical properties of Arctic aerosol particles collected at the Zeppelin station during the aerosol transition period in May and June of 20042008In: Tellus. Series B: Chemical and Physical Meteorology, Vol. 60, no 3, p. 405-415Article in journal (Refereed)
  • 19. Bianchi, F.
    et al.
    Sinclair, V. A.
    Aliaga, D.
    Zha, Q.
    Scholz, W.
    Wu, Cheng
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Heikkinen, L.
    Modini, R.
    Partoll, E.
    Velarde, F.
    Moreno, I.
    Gramlich, Yvette
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Huang, W.
    Koenig, A. M.
    Leiminger, M.
    Enroth, J.
    Peräkylä, O.
    Marinoni, A.
    Xuemeng, C.
    Blacutt, L.
    Forno, R.
    Gutierrez, R.
    Ginot, P.
    Uzu, G.
    Facchini, M. C.
    Gilardoni, S.
    Gysel-Beer, M.
    Cai, R.
    Petäjä, T.
    Rinaldi, M.
    Saathoff, H.
    Sellegri, K.
    Worsnop, D.
    Artaxo, P.
    Hansel, A.
    Kulmala, M.
    Wiedensohler, A.
    Laj, P.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Carbone, S.
    Andrade, M.
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science.
    The SALTENA Experiment: Comprehensive Observations of Aerosol Sources, Formation, and Processes in the South American Andes2022In: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 103, no 2, p. E212-E229Article in journal (Refereed)
    Abstract [en]

    This paper presents an introduction to the Southern Hemisphere High Altitude Experiment on Particle Nucleation and Growth (SALTENA). This field campaign took place between December 2017 and June 2018 (wet to dry season) at Chacaltaya (CHC), a GAW (Global Atmosphere Watch) station located at 5,240 m MSL in the Bolivian Andes. Concurrent measurements were conducted at two additional sites in El Alto (4,000 m MSL) and La Paz (3,600 m MSL). The overall goal of the campaign was to identify the sources, understand the formation mechanisms and transport, and characterize the properties of aerosol at these stations. State-of-the-art instruments were brought to the station complementing the ongoing permanent GAW measurements, to allow a comprehensive description of the chemical species of anthropogenic and biogenic origin impacting the station and contributing to new particle formation. In this overview we first provide an assessment of the complex meteorology, airmass origin, and boundary layer-free troposphere interactions during the campaign using a 6-month high-resolution Weather Research and Forecasting (WRF) simulation coupled with Flexible Particle dispersion model (FLEXPART). We then show some of the research highlights from the campaign, including (i) chemical transformation processes of anthropogenic pollution while the air masses are transported to the CHC station from the metropolitan area of La Paz-El Alto, (ii) volcanic emissions as an important source of atmospheric sulfur compounds in the region, (iii) the characterization of the compounds involved in new particle formation, and (iv) the identification of long-range-transported compounds from the Pacific or the Amazon basin. We conclude the article with a presentation of future research foci. The SALTENA dataset highlights the importance of comprehensive observations in strategic high-altitude locations, especially the undersampled Southern Hemisphere.

  • 20.
    Bourgeois, Quentin
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Igel, Matthew R.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ubiquity and impact of thin mid-level clouds in the tropics2016In: Nature Communications, E-ISSN 2041-1723, Vol. 7, article id 12432Article in journal (Refereed)
    Abstract [en]

    Clouds are crucial for Earth's climate and radiation budget. Great attention has been paid to low, high and vertically thick tropospheric clouds such as stratus, cirrus and deep convective clouds. However, much less is known about tropospheric mid-level clouds as these clouds are challenging to observe in situ and difficult to detect by remote sensing techniques. Here we use Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite observations to show that thin mid-level clouds (TMLCs) are ubiquitous in the tropics. Supported by high-resolution regional model simulations, we find that TMLCs are formed by detrainment from convective clouds near the zero-degree isotherm. Calculations using a radiative transfer model indicate that tropical TMLCs have a cooling effect on climate that could be as large in magnitude as the warming effect of cirrus. We conclude that more effort has to be made to understand TMLCs, as their influence on cloud feedbacks, heat and moisture transport, and climate sensitivity could be substantial.

  • 21.
    Bourgeois, Quentin
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Aerosol transport over the Andes from the Amazon Basin to the remote Pacific Ocean: A multiyear CALIOP assessment2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 16, p. 8411-8425Article in journal (Refereed)
    Abstract [en]

    Six years (200702012) of data from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite instrument were used to investigate the vertical distribution and transport of aerosols over the tropical South American continent and the southeast Pacific Ocean. The multiyear aerosol extinction assessment indicates that aerosols, mainly biomass burning particles emitted during the dry season in the Amazon Basin, are lifted in significant amounts over the Andes. The aerosols are mainly transported in the planetary boundary layer between the surface and 2 km altitude with an aerosol extinction maximum near the surface. During the transport toward the Andes, the aerosol extinction decreases at a rate of 0.02 km(-1) per kilometer of altitude likely due to dilution and deposition processes. Aerosols reaching the top of the Andes, at altitudes typically between 4 and 5 km, are entrained into the free troposphere (FT) over the southeast Pacific Ocean. A comparison between CALIOP observations and ERA-Interim reanalysis data indicates that during their long-range transport over the tropical Pacific Ocean, these aerosols are slowly transported toward the marine boundary layer by the large-scale subsidence at a rate of 0.4 cm s(-1). The observed vertical/horizontal transport ratio is 0.700.8 m km(-1) Continental aerosols linked to transport over the Andes can be traced on average over 4000 km away from the continent indicating an aerosol residence time of 809 days in the FT over the Pacific Ocean. The FT aerosol optical depth (AOD) above the Pacific Ocean near South American coast accounts on average for 6% and 25% of the total AOD during the season of low and high biomass burning, respectively. This result shows that, during the biomass burning season, continental aerosols largely influence the AOD over the remote southeast Pacific Ocean. Overall, FT AOD decrease exponentially with the distance to continental sources at a rate of about 10% per degree of longitude over the Pacific Ocean.

  • 22.
    Bourgeois, Quentin
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Renard, Jean-Baptiste
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Devasthale, Abhay
    Bender, Frida A. -M.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Berthet, Gwenaël
    Tackett, Jason L.
    How much of the global aerosol optical depth is found in the boundary layer and free troposphere?2018In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 18, no 10, p. 7709-7720Article in journal (Refereed)
    Abstract [en]

    The global aerosol extinction from the CALIOP space lidar was used to compute aerosol optical depth (AOD) over a 9-year period (2007-2015) and partitioned between the boundary layer (BL) and the free troposphere (FT) using BL heights obtained from the ERA-Interim archive. The results show that the vertical distribution of AOD does not follow the diurnal cycle of the BL but remains similar between day and night highlighting the presence of a residual layer during night. The BL and FT contribute 69 and 31 %, respectively, to the global tropospheric AOD during daytime in line with observations obtained in Aire sur l'Adour (France) using the Light Optical Aerosol Counter (LOAC) instrument. The FT AOD contribution is larger in the tropics than at mid-latitudes which indicates that convective transport largely controls the vertical profile of aerosols. Over oceans, the FT AOD contribution is mainly governed by long-range transport of aerosols from emission sources located within neighboring continents. According to the CALIOP aerosol classification, dust and smoke particles are the main aerosol types transported into the FT. Overall, the study shows that the fraction of AOD in the FT - and thus potentially located above low-level clouds - is substantial and deserves more attention when evaluating the radiative effect of aerosols in climate models. More generally, the results have implications for processes determining the overall budgets, sources, sinks and transport of aerosol particles and their description in atmospheric models.

  • 23. Boy, Michael
    et al.
    Thomson, Erik S.
    Acosta Navarro, Juan-C.
    Arnalds, Olafur
    Batchvarova, Ekaterina
    Back, Jaana
    Berninger, Frank
    Bilde, Merete
    Brasseur, Zoe
    Dagsson-Waldhauserova, Pavla
    Castarede, Dimitri
    Dalirian, Maryam
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    de Leeuw, Gerrit
    Dragosics, Monika
    Duplissy, Ella-Maria
    Duplissy, Jonathan
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Fang, Keyan
    Gallet, Jean-Charles
    Glasius, Marianne
    Gryning, Sven-Erik
    Grythe, Henrik
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. NILU–Norwegian Institute for Air Research, Norway.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Isaksson, Elisabeth
    Iversen, Trond
    Jonsdottir, Ingibjorg
    Kasurinen, Ville
    Kirkevag, Alf
    Korhola, Atte
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kristjansson, Jon Egill
    Lappalainen, Hanna K.
    Lauri, Antti
    Lepparanta, Matti
    Lihavainen, Heikki
    Makkonen, Risto
    Massling, Andreas
    Meinander, Outi
    Nilsson, E. Douglas
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Olafsson, Haraldur
    Pettersson, Jan B. C.
    Prisle, Nonne L.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Roldin, Pontus
    Ruppel, Meri
    Salter, Matthew
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Sand, Maria
    Seland, Oyvind
    Seppa, Heikki
    Skov, Henrik
    Soares, Joana
    Stohl, Andreas
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Svensson, Jonas
    Swietlicki, Erik
    Tabakova, Ksenia
    Thorsteinsson, Throstur
    Virkkula, Aki
    Weyhenmeyer, Gesa A.
    Wu, Yusheng
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kulmala, Markku
    Interactions between the atmosphere, cryosphere, and ecosystems at northern high latitudes2019In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 19, no 3, p. 2015-2061Article in journal (Refereed)
    Abstract [en]

    The Nordic Centre of Excellence CRAICC (Cryosphere-Atmosphere Interactions in a Changing Arctic Climate), funded by NordForsk in the years 2011-2016, is the largest joint Nordic research and innovation initiative to date, aiming to strengthen research and innovation regarding climate change issues in the Nordic region. CRAICC gathered more than 100 scientists from all Nordic countries in a virtual centre with the objectives of identifying and quantifying the major processes controlling Arctic warming and related feedback mechanisms, outlining strategies to mitigate Arctic warming, and developing Nordic Earth system modelling with a focus on short-lived climate forcers (SLCFs), including natural and anthropogenic aerosols. The outcome of CRAICC is reflected in more than 150 peer-reviewed scientific publications, most of which are in the CRAICC special issue of the journal Atmospheric Chemistry and Physics. This paper presents an overview of the main scientific topics investigated in the centre and provides the reader with a state-of-the-art comprehensive summary of what has been achieved in CRAICC with links to the particular publications for further detail. Faced with a vast amount of scientific discovery, we do not claim to completely summarize the results from CRAICC within this paper, but rather concentrate here on the main results which are related to feedback loops in climate change-cryosphere interactions that affect Arctic amplification.

  • 24. Boyer, Matthew
    et al.
    Aliaga, Diego
    Pernov, Jakob Boyd
    Angot, Hélène
    Quéléver, Lauriane L. J.
    Dada, Lubna
    Heutte, Benjamin
    Dall'Osto, Manuel
    Beddows, David C. S.
    Brasseur, Zoé
    Beck, Ivo
    Bucci, Silvia
    Duetsch, Marina
    Stohl, Andreas
    Laurila, Tiia
    Asmi, Eija
    Massling, Andreas
    Thomas, Daniel Charles
    Klenø Nøjgaard, Jakob
    Chan, Tak
    Sharma, Sangeeta
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Bianchi, Federico
    Lehtipalo, Katrianne
    Wiedensohler, Alfred
    Weinhold, Kay
    Kulmala, Markku
    Petäjä, Tuukka
    Sipilä, Mikko
    Schmale, Julia
    Jokinen, Tuija
    A full year of aerosol size distribution data from the central Arctic under an extreme positive Arctic Oscillation: insights from the Multidisciplinarydrifting Observatory for the Study of Arctic Climate (MOSAiC) expedition2023In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 23, no 1, p. 389-415Article in journal (Refereed)
    Abstract [en]

    The Arctic environment is rapidly changing due to accelerated warming in the region. The warming trend is driving a decline in sea ice extent, which thereby enhances feedback loops in the surface energy budget in the Arctic. Arctic aerosols play an important role in the radiative balance and hence the climate response in the region, yet direct observations of aerosols over the Arctic Ocean are limited. In this study, we investigate the annual cycle in the aerosol particle number size distribution (PNSD), particle number concentration (PNC), and black carbon (BC) mass concentration in the central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. This is the first continuous, year-long data set of aerosol PNSD ever collected over the sea ice in the central Arctic Ocean. We use a k-means cluster analysis, FLEXPART simulations, and inverse modeling to evaluate seasonal patterns and the influence of different source regions on the Arctic aerosol population. Furthermore, we compare the aerosol observations to land-based sites across the Arctic, using both long-term measurements and observations during the year of the MOSAiC expedition (2019–2020), to investigate interannual variability and to give context to the aerosol characteristics from within the central Arctic. Our analysis identifies that, overall, the central Arctic exhibits typical seasonal patterns of aerosols, including anthropogenic influence from Arctic haze in winter and secondary aerosol processes in summer. The seasonal pattern corresponds to the global radiation, surface air temperature, and timing of sea ice melting/freezing, which drive changes in transport patterns and secondary aerosol processes. In winter, the Norilsk region in Russia/Siberia was the dominant source of Arctic haze signals in the PNSD and BC observations, which contributed to higher accumulation-mode PNC and BC mass concentrations in the central Arctic than at land-based observatories. We also show that the wintertime Arctic Oscillation (AO) phenomenon, which was reported to achieve a record-breaking positive phase during January–March 2020, explains the unusual timing and magnitude of Arctic haze across the Arctic region compared to longer-term observations. In summer, the aerosol PNCs of the nucleation and Aitken modes are enhanced; however, concentrations were notably lower in the central Arctic over the ice pack than at land-based sites further south. The analysis presented herein provides a current snapshot of Arctic aerosol processes in an environment that is characterized by rapid changes, which will be crucial for improving climate model predictions, understanding linkages between different environmental processes, and investigating the impacts of climate change in future Arctic aerosol studies.

  • 25. Brean, James
    et al.
    Beddows, David C. S.
    Harrison, Roy M.
    Song, Congbo
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Freud, Eyal
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Massling, Andreas
    Skov, Henrik
    Asmi, Eija
    Lupi, Angelo
    Dall'Osto, Manuel
    Collective geographical ecoregions and precursor sources driving Arctic new particle formation2023In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 23, no 3, p. 2183-2198Article in journal (Refereed)
    Abstract [en]

    The Arctic is a rapidly changing ecosystem, with complex ice–ocean–atmosphere feedbacks. An important process is new particle formation (NPF), from gas-phase precursors, which provides a climate forcing effect. NPF has been studied comprehensively at different sites in the Arctic, ranging from those in the High Arctic and those at Svalbard to those in the continental Arctic, but no harmonised analysis has been performed on all sites simultaneously, with no calculations of key NPF parameters available for some sites. Here, we analyse the formation and growth of new particles from six long-term ground-based stations in the Arctic (Alert, Villum, Tiksi, Zeppelin Mountain, Gruvebadet, and Utqiaġvik). Our analysis of particle formation and growth rates in addition to back-trajectory analysis shows a summertime maxima in the frequency of NPF and particle formation rate at all sites, although the mean frequency and particle formation rates themselves vary greatly between sites, with the highest at Svalbard and lowest in the High Arctic. The summertime growth rate, condensational sinks, and vapour source rates show a slight bias towards the southernmost sites, with vapour source rates varying by around an order of magnitude between the northernmost and southernmost sites. Air masses back-trajectories during NPF at these northernmost sites are associated with large areas of sea ice and snow, whereas events at Svalbard are associated with more sea ice and ocean regions. Events at the southernmost sites are associated with large areas of land and sea ice. These results emphasise how understanding the geographical variation in surface type across the Arctic is key to understanding secondary aerosol sources and providing a harmonised analysis of NPF across the Arctic.

  • 26. Chauvigné, Aurélien
    et al.
    Aliaga, Diego
    Sellegri, Karine
    Montoux, Nadège
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Močnik, Griša
    Moreno, Isabel
    Müller, Thomas
    Pandolfi, Marco
    Velarde, Fernando
    Weinhold, Kay
    Ginot, Patrick
    Wiedensohler, Alfred
    Andrade, Marcos
    Laj, Paolo
    Biomass burning and urban emission impacts in the Andes Cordillera region based on in situ measurements from the Chacaltaya observatory, Bolivia (5240 m a.s.l.)2019In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 19, no 23, p. 14805-14824Article in journal (Refereed)
    Abstract [en]

    This study documents and analyses a 4-year continuous record of aerosol optical properties measured at the Global Atmosphere Watch (GAW) station of Chacaltaya (CHC; 5240 m a.s.l.), in Bolivia. Records of particle light scattering and particle light absorption coefficients are used to investigate how the high Andean Cordillera is affected by both long-range transport and by the fast-growing agglomeration of La Paz-El Alto, located approximately 20 km away and 1.5 km below the sampling site. The extended multiyear record allows us to study the properties of aerosol particles for different air mass types, during wet and dry seasons, also covering periods when the site was affected by biomass burning in the Bolivian lowlands and the Amazon Basin. The absorption, scattering, and extinction coefficients (median annual values of 0.74, 12.14, and 12.96 Mm(-1) respectively) show a clear seasonal variation with low values during the wet season (0.57, 7.94, and 8.68 Mm(-1) respectively) and higher values during the dry season (0.80, 11.23, and 14.51 Mm(-1) respectively). The record is driven by variability at both seasonal and diurnal scales. At a diurnal scale, all records of intensive and extensive aerosol properties show a pronounced variation (daytime maximum, night-time minimum), as a result of the dynamic and convective effects. The particle light absorption, scattering, and extinction coefficients are on average 1.94, 1.49, and 1.55 times higher respectively in the turbulent thermally driven conditions than the more stable conditions, due to more efficient transport from the boundary layer. Retrieved intensive optical properties are significantly different from one season to the other, reflecting the changing aerosol emission sources of aerosol at a larger scale. Using the wavelength dependence of aerosol particle optical properties, we discriminated between contributions from natural (mainly mineral dust) and anthropogenic (mainly biomass burning and urban transport or industries) emissions according to seasons and local circulation. The main sources influencing measurements at CHC are from the urban area of La Paz-El Alto in the Altiplano and from regional biomass burning in the Amazon Basin. Results show a 28 % to 80 % increase in the extinction coefficients during the biomass burning season with respect to the dry season, which is observed in both tropospheric dynamic conditions. From this analysis, long-term observations at CHC provide the first direct evidence of the impact of biomass burning emissions of the Amazon Basin and urban emissions from the La Paz area on atmospheric optical properties at a remote site all the way to the free troposphere.

  • 27. Choi, J. H.
    et al.
    Jang, E.
    Yoon, Y. J.
    Park, J. Y.
    Kim, T.-W.
    Becagli, S.
    Caiazzo, L.
    Cappelletti, D.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Eleftheria, K.
    Park, K.-T.
    Jang, K. S.
    Influence of Biogenic Organics on the Chemical Composition of Arctic Aerosols2019In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 33, no 10, p. 1238-1250Article in journal (Refereed)
    Abstract [en]

    We use an ultrahigh-resolution 15-T Fourier transform ion cyclotron resonance mass spectrometer to elucidate the compositional changes in Arctic organic aerosols collected at Ny-angstrom lesund, Svalbard, in May 2015. The Fourier transform ion cyclotron resonance mass spectrometer analysis of airborne organic matter provided information on the molecular compositions of aerosol particles collected during the Arctic spring period. The air mass transport history, combined with satellite-derived geographical information and chlorophyll concentration data, revealed that the molecular compositions of organic aerosols drastically differed depending on the origin of the potential source region. The protein and lignin compound populations contributed more than 70% of the total intensity of assigned molecules when the air masses mainly passed over the ocean region. Interestingly, the intensity of microbe-derived organics (protein and carbohydrate compounds) was positively correlated with the air mass exposure to phytoplankton biomass proxied as chlorophyll. Furthermore, the intensities of lignin and unsaturated hydrocarbon compounds, typically derived from terrestrial vegetation, increased with an increase in the advection time of the air mass over the ocean domain. These results suggest that the accumulation of dissolved biogenic organics in the Arctic Ocean possibly derived from both phytoplankton and terrestrial vegetation could significantly influence the chemical properties of Arctic organic aerosols during a productive spring period. The interpretation of molecular changes in organic aerosols using an ultrahigh-resolution mass spectrometer could provide deep insight for understanding organic aerosols in the atmosphere over the Arctic and the relationship of organic aerosols with biogeochemical processes in terms of aerosol formation and environmental changes.

  • 28. Dall' Osto, M.
    et al.
    Beddows, D. C. S.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Yoon, Y. J.
    Park, Ki-Tae
    Becagli, S.
    Udisti, R.
    Onasch, T.
    O'Dowd, C. D.
    Simo, R.
    Harrison, Roy M.
    Arctic sea ice melt leads to atmospheric new particle formation2017In: Scientific Reports, E-ISSN 2045-2322, Vol. 7, article id 3318Article in journal (Refereed)
    Abstract [en]

    Atmospheric new particle formation (NPF) and growth significantly influences climate by supplying new seeds for cloud condensation and brightness. Currently, there is a lack of understanding of whether and how marine biota emissions affect aerosol-cloud-climate interactions in the Arctic. Here, the aerosol population was categorised via cluster analysis of aerosol size distributions taken at Mt Zeppelin (Svalbard) during a 11 year record. The daily temporal occurrence of NPF events likely caused by nucleation in the polar marine boundary layer was quantified annually as 18%, with a peak of 51% during summer months. Air mass trajectory analysis and atmospheric nitrogen and sulphur tracers link these frequent nucleation events to biogenic precursors released by open water and melting sea ice regions. The occurrence of such events across a full decade was anti-correlated with sea ice extent. New particles originating from open water and open pack ice increased the cloud condensation nuclei concentration background by at least ca. 20%, supporting a marine biosphere-climate link through sea ice melt and low altitude clouds that may have contributed to accelerate Arctic warming. Our results prompt a better representation of biogenic aerosol sources in Arctic climate models.

  • 29. Dall'Osto, Manuel
    et al.
    Beddows, David C. S.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Harrison, Roy M.
    Lupi, Angelo
    Vitale, Vito
    Becagli, Silvia
    Traversi, Rita
    Park, Ki-Tae
    Yoon, Young Jun
    Massling, Andreas
    Skov, Henrik
    Lange, Robert
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Simultaneous measurements of aerosol size distributions at three sites in the European high Arctic2019In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 19, no 11, p. 7377-7395Article in journal (Refereed)
    Abstract [en]

    Aerosols are an integral part of the Arctic climate system due to their direct interaction with radiation and indirect interaction through cloud formation. Understanding aerosol size distributions and their dynamics is crucial for the ability to predict these climate relevant effects. When of favourable size and composition, both long-rangetransported - and locally formed particles - may serve as cloud condensation nuclei (CCN). Small changes of composition or size may have a large impact on the low CCN concentrations currently characteristic of the Arctic environment. We present a cluster analysis of particle size distributions (PSDs; size range 8-500 nm) simultaneously collected from three high Arctic sites during a 3-year period (20132015). Two sites are located in the Svalbard archipelago: Zeppelin research station (ZEP; 474 m above ground) and the nearby Gruvebadet Observatory (GRU; about 2 km distance from Zeppelin, 67 m above ground). The third site (Villum Research Station at Station Nord, VRS; 30 m above ground) is 600 km west-northwest of Zeppelin, at the tip of northeastern Greenland. The GRU site is included in an inter-site comparison for the first time. K-means cluster analysis pro- vided eight specific aerosol categories, further combined into broad PSD classes with similar characteristics, namely pristine low concentrations (12 %-14 % occurrence), new particle formation (16 %-32 %), Aitken (21 %-35 %) and accumulation (20 %-50 %). Confined for longer time periods by consolidated pack sea ice regions, the Greenland site GRU shows PSDs with lower ultrafine-mode aerosol concentrations during summer but higher accumulation-mode aerosol concentrations during winter, relative to the Svalbard sites. By association with chemical composition and cloud condensation nuclei properties, further conclusions can be derived. Three distinct types of accumulation-mode aerosol are observed during winter months. These are associated with sea spray (largest detectable sizes, > 400 nm), Arctic haze (main mode at 150 nm) and aged accumulation-mode (main mode at 220 nm) aerosols. In contrast, locally produced particles, most likely of marine biogenic origin, exhibit size distributions dominated by the nucleation and Aitken mode during summer months. The obtained data and analysis point towards future studies, including apportioning the relative contribution of primary and secondary aerosol formation processes and elucidating anthropogenic aerosol dynamics and transport and removal processes across the Greenland Sea. In order to address important research questions in the Arctic on scales beyond a singular station or measurement events, it is imperative to continue strengthening international scientific cooperation.

  • 30.
    Ekman, Annica
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Engström, Anders
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    de Reus, Marian
    Max Planck Institute for Chemistry, Mainz, Germany.
    Williams, Jonathan
    Max Planck Institute for Chemistry, Mainz, Germany.
    Andreae, Meinrat
    Max Planck Institute for Chemistry, Mainz, Germany.
    Do organics contribute to small particle formation in the Amazonian upper troposphere?2008In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, no L17810, p. 5-Article in journal (Refereed)
    Abstract [en]

    3-D cloud-resolving model simulations including explicit aerosol physics and chemistry are compared with observations of upper tropospheric (12 km) aerosol size distributions over the Amazon Basin. The model underestimates the aerosol number concentration for all modes, especially the nucleation mode (d < 18 nm). We show that a boundary layer SO2 mixing ratio of approximately 5 ppb would be needed in order to reproduce the high nucleation mode number concentrations observed. This high SO2 mixing ratio is very unlikely for the pristine Amazon Basin at this time of the year. Hence, it is suggested that vapours other than H2SO4 participate in the formation and growth of small aerosols. Using activation nucleation theory together with a small (0.4–10%) secondary organic aerosol mass yield, we show that isoprene has the potential of substantially increasing the number of small particles formed as well as reducing the underestimate for the larger aerosol modes.

  • 31.
    Ekman, Annica
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Meteorology.
    Engström, Anders
    Stockholm University, Faculty of Science, Department of Meteorology.
    Ström, Johan
    Department of Applied Environmental Science (ITM).
    de Reus, Marian
    Williams, Jonathan
    Andreae, Meinrat O.
    Do organics contribute to new particle formation in the Amazonian upper troposphere?2008In: Geophysical Research Letters, Vol. 35, p. L17810-Article in journal (Refereed)
    Abstract [en]

    3-D cloud-resolving model simulations including explicit aerosol physics and chemistry are compared with observations of upper tropospheric (12 km) aerosol size distributions over the Amazon Basin. The model underestimates the aerosol number concentration for all modes, especially the nucleation mode (d< 18nm). We show that a boundary layer SO2 mixing ratio of approximately 5 ppb would be needed in order to reproduce the high nucleation mode number concentrations observed. This high SO2 mixing ratio is very unlikely for the pristine Amazon Basin at this time of the year. Hence, it is suggested that vapours other than H2SO4 participate in the formation and growth of small aerosols. Using activation nucleation theory together with a small (0.4-10%) secondary organic aerosol mass yield, we show that isoprene has the potential of substantially increasing the number of small particles formed as well as reducing the underestimate for the larger aerosol modes.

  • 32.
    Engström, Anders
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M.L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    de Reus, Marian
    Wang, Chien
    Observational and modelling evidence of tropical deep convective clouds as a source of mid-tropospheric accumulation mode aerosols2008In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 35, p. L23813-Article in journal (Refereed)
    Abstract [en]

    High concentrations (up to 550 cm−3 STP) of aerosols in the accumulation mode (>0.12 μm) were observed by aircraft above 7.5 km altitude in the dynamically active regions of several deep convective clouds during the INDOEX campaign. Using a coupled 3-D aerosol-cloud-resolving model, we find that significant evaporation of hydrometeors due to strong updrafts and exchange with ambient air occurs at the boundaries and within the cloud tower. Assuming that each evaporated hydrometeor release an aerosol, an increase in the aerosol concentration by up to 600 cm−3 STP is found in the model at altitudes between 6 and 10 km. The evaporation and release of aerosols occur as the cloud develops, suggesting that deep convective clouds are important sources of mid-tropospheric aerosols during their active lifetime. This source may significantly impact the vertical distribution as well as long-range transport of aerosols in the free troposphere.

  • 33. Engvall, Ann-Christine
    et al.
    Strom, Johan
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Schlager, Hans
    Minikin, Andreas
    The radiative effect of an aged, internally mixed Arctic aerosol originating from lower-latitude biomass burning2009In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 61, no 4, p. 677-684Article in journal (Refereed)
    Abstract [en]

    Arctic-haze layers and their radiative effects have been investigated previously in numerous studies as they are known to have an impact on the regional climate. In this study, we report on an event of an elevated aerosol layer, notably consisting of high-absorbing soot particles, observed in the European Arctic free troposphere the 2007 April 14 during the ASTAR 2007 campaign. The ca. 0.5 km vertically thick aerosol layer located at an altitude of around 3 km had a particle-size distribution mode around 250 nm diameter. In this study, we quantify the radiative effect aerosol layers have on the Arctic atmosphere by using in situ observations. Measurements of particles size segregated temperature stability using thermal denuders, indicate that the aerosol in the optically active size range was chemically internally mixed. In the plume, maximum observed absorption and scattering coefficients were 3 x 10(-6) and 20 x 10(-6) m(-1), respectively. Observed microphysical and optical properties were used to constrain calculations of heating rates of an internally mixed aerosol assuming two different surface albedos that represent snow/ice covered and open ocean. The average profile resulted in a heating rate in the layer of 0.2 K d(-1) for the high-albedo case and 0.15 K d(-1) for the low albedo case. This calculated dependence on albedo based on actual observations corroborates previous numerical simulations. The heating within the plume resulted in a measurable signal shown as an enhancement in the temperature of a few tenths of a degree. Although the origin of the aerosol plume could not unambiguously be determined, the microphysical properties of the aerosol had strong similarities with previously reported biomass burning plumes. With a changing climate, short-lived pollutants such as biomass plumes may become more frequent in the Arctic and have important radiative effects at regional scale.

  • 34. Fahlgren, Camilla
    et al.
    Gómez-Consarnau, Laura
    Zábori, Julia
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Lindh, Markus V.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mårtensson, E. Monica
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Uppsala University, Sweden.
    Nilsson, Douglas
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Pinhassi, Jarone
    Seawater mesocosm experiments in the Arctic uncover differential transfer of marine bacteria to aerosols2015In: Environmental Microbiology Reports, ISSN 1758-2229, E-ISSN 1758-2229, Vol. 7, no 3, p. 460-470Article in journal (Refereed)
    Abstract [en]

    Biogenic aerosols critically control atmospheric processes. However, although bacteria constitute major portions of living matter in seawater, bacterial aerosolization from oceanic surface layers remains poorly understood. We analysed bacterial diversity in seawater and experimentally generated aerosols from three Kongsfjorden sites, Svalbard. Construction of 16S rRNA gene clone libraries from paired seawater and aerosol samples resulted in 1294 sequences clustering into 149 bacterial and 34 phytoplankton operational taxonomic units (OTUs). Bacterial communities in aerosols differed greatly from corresponding seawater communities in three out of four experiments. Dominant populations of both seawater and aerosols were Flavobacteriia, Alphaproteobacteria and Gammaproteobacteria. Across the entire dataset, most OTUs from seawater could also be found in aerosols; in each experiment, however, several OTUs were either selectively enriched in aerosols or little aerosolized. Notably, a SAR11 clade OTU was consistently abundant in the seawater, but was recorded in significantly lower proportions in aerosols. A strikingly high proportion of colony-forming bacteria were pigmented in aerosols compared with seawater, suggesting that selection during aerosolization contributes to explaining elevated proportions of pigmented bacteria frequently observed in atmospheric samples. Our findings imply that atmospheric processes could be considerably influenced by spatiotemporal variations in the aerosolization efficiency of different marine bacteria.

  • 35.
    Freud, Eyal
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Leaitch, Richard
    Nguyen, Quynh T.
    Massling, Andreas
    Skov, Henrik
    Barrie, Leonard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Pan-Arctic aerosol number size distributions: seasonality and transport patterns2017In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, no 13, p. 8101-8128Article in journal (Refereed)
    Abstract [en]

    The Arctic environment has an amplified response to global climatic change. It is sensitive to human activities that mostly take place elsewhere. For this study, a multi-year set of observed aerosol number size distributions in the diameter range of 10 to 500 nm from five sites around the Arctic Ocean (Alert, Villum Research Station - Station Nord, Zeppelin, Tiksi and Barrow) was assembled and analysed. A cluster analysis of the aerosol number size distributions revealed four distinct distributions. Together with Lagrangian air parcel back-trajectories, they were used to link the observed aerosol number size distributions with a variety of transport regimes. This analysis yields insight into aerosol dynamics, transport and removal processes, on both an intra- and an inter-monthly scale. For instance, the relative occurrence of aerosol number size distributions that indicate new particle formation (NPF) event is near zero during the dark months, increases gradually to similar to 40% from spring to summer, and then collapses in autumn. Also, the likelihood of Arctic haze aerosols is minimal in summer and peaks in April at all sites. The residence time of accumulation-mode particles in the Arctic troposphere is typically long enough to allow tracking them back to their source regions. Air flow that passes at low altitude over central Siberia and western Russia is associated with relatively high concentrations of accumulation-mode particles (N-acc) at all five sites - often above 150 cm(-3). There are also indications of air descending into the Arctic boundary layer after transport from lower latitudes. The analysis of the back-trajectories together with the meteorological fields along them indicates that the main driver of the Arctic annual cycle of N-acc, on the larger scale, is when atmospheric transport covers the source regions for these particles in the 10-day period preceding the observations in the Arctic. The scavenging of these particles by precipitation is shown to be important on a regional scale and it is most active in summer. Cloud processing is an additional factor that enhances the N-acc annual cycle. There are some consistent differences between the sites that are beyond the year-to-year variability. They are the result of differences in the proximity to the aerosol source regions and to the Arctic Ocean sea-ice edge, as well as in the exposure to free-tropospheric air and in precipitation patterns - to mention a few. Hence, for most purposes, aerosol observations from a single Arctic site cannot represent the entire Arctic region. Therefore, the results presented here are a powerful observational benchmark for evaluation of detailed climate and air chemistry modelling studies of aerosols throughout the vast Arctic region.

  • 36.
    Gonzalez, Nelida J. D.
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Borg-Karlson, A. -K
    Artaxo, P.
    Guenther, A.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). University of Helsinki, Finland.
    Noziere, B.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Noone, Kevin
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Primary and secondary organics in the tropical Amazonian rainforest aerosols: chiral analysis of 2-methyltetraols2014In: Environmental Science Processes and Impacts, ISSN 2050-7887, Vol. 16, no 6, p. 1413-1421Article in journal (Refereed)
    Abstract [en]

    This work presents the application of a new method to facilitate the distinction between biologically produced (primary) and atmospherically produced (secondary) organic compounds in ambient aerosols based on their chirality. The compounds chosen for this analysis were the stereomers of 2-methyltetraols, (2R, 3S)- and (2S, 3R)-methylerythritol, (L- and D-form, respectively), and (2S, 3S)- and (2R, 3R)-methylthreitol (L- and D-form), shown previously to display some enantiomeric excesses in atmospheric aerosols, thus to have at least a partial biological origin. In this work PM10 aerosol fractions were collected in a remote tropical rainforest environment near Manaus, Brazil, between June 2008 and June 2009 and analysed. Both 2-methylerythritol and 2-methylthreitol displayed a net excess of one enantiomer (either the L- or the D-form) in 60 to 72% of these samples. These net enantiomeric excesses corresponded to compounds entirely biological but accounted for only about 5% of the total 2-methyltetrol mass in all the samples. Further analysis showed that, in addition, a large mass of the racemic fractions (equal mixtures of D- and L-forms) was also biological. Estimating the contribution of secondary reactions from the isomeric ratios measured in the samples (=ratios 2-methylthreitol over 2-methylerythritol), the mass fraction of secondary methyltetrols in these samples was estimated to a maximum of 31% and their primary fraction to a minimum of 69%. Such large primary fractions could have been expected in PM10 aerosols, largely influenced by biological emissions, and would now need to be investigated in finer aerosols. This work demonstrates the effectiveness of chiral and isomeric analyses as the first direct tool to assess the primary and secondary fractions of organic aerosols.

  • 37.
    Gonzalez, Nelida J. D.
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Borg-Karlson, Anna-Karin
    Redeby, Johan Pettersson
    Noziere, Barbara
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Pei, Yuxin
    Dommen, Josef
    Prevot, Andre S. H.
    New method for resolving the enantiomeric composition of 2-methyltetrols in atmospheric organic aerosols2011In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 1218, no 51, p. 9288-9294Article in journal (Refereed)
    Abstract [en]

    In order to facilitate the determination of the primary and secondary origin of atmospheric organic aerosols, a novel method involving chiral capillary gas chromatography coupled with mass spectrometry has been developed and validated. The method was focused on the analysis of 2-methylerythritol and 2-methylthreitol, considered to be tracers of secondary organic aerosols from the oxidation of atmospheric isoprene. The method was validated by performing various tests using authentic standards, including pure enantiomeric standards. The result showed that the analytical method itself does not affect the enantiomeric composition of the samples analyzed. The method was applied on atmospheric aerosols from a boreal forest collected in Aspvreten, Sweden and on laboratory samples obtained from liquid phase oxidation of isoprene and smog chamber experiments. Aerosol samples contained one enantiomer of 2-methylerythritol in significantly larger quantities than the others. In contrast, the liquid-phase oxidation of isoprene and its gas-phase oxidation in the smog chamber produced all enantiomers in equal quantities. The results obtained where the enantiomer fraction, EF, is larger than 0.50 suggest that 2-methyltetrols in atmospheric aerosols may also have biological origin. Information about the differences between enantiomer fractions obtained using this method brings new insights in the area of atmospheric aerosols.

  • 38.
    González, N
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Borg-Karlson, A.-K.
    Nozière, B
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, R
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Levula, J.
    Artaxo, P.
    New analytical technique for the identification of tracers for secondary organic material in atmospheric aerosols2008In: European Aerosol Conference (EAC) 2008: 24-29 August, Thessaloniki, Greece, 2008Conference paper (Refereed)
  • 39.
    Graham, Emelie L.
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Wu, Cheng
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Bell, David M.
    Bertand, Amelie
    Haslett, Sophie L.
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Baltensperger, Urs
    El Haddad, Imad
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Volatility of aerosol particles from NO3 oxidation of various biogenic organic precursorsManuscript (preprint) (Other academic)
  • 40.
    Graham, Emelie L.
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Wu, Cheng
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Bell, David M.
    Bertrand, Amelie
    Haslett, Sophie L.
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Baltensperger, Urs
    El Haddad, Imad
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Volatility of aerosol particles from NO3 oxidation of various biogenic organic precursors2023In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 23, no 13, p. 7347-7362Article in journal (Refereed)
    Abstract [en]

    Secondary organic aerosol (SOA) is formed through the oxidation of volatile organic compounds (VOCs), which can be of both natural and anthropogenic origin. While the hydroxyl radical (OH) and ozone (O3) are the main atmospheric oxidants during the day, the nitrate radical (NO3) becomes more important during the nighttime. Yet, atmospheric nitrate chemistry has received less attention compared to OH and O3.

    The Nitrate Aerosol and Volatility Experiment (NArVE) aimed to study the NO3-induced SOA formation and evolution from three biogenic VOCs (BVOCs), namely isoprene, α-pinene, and β-caryophyllene. The volatility of aerosol particles was studied using isothermal evaporation chambers, temperature-dependent evaporation in a volatility tandem differential mobility analyzer (VTDMA), and thermal desorption in a filter inlet for gases and aerosols coupled to a chemical ionization mass spectrometer (FIGAERO-CIMS). Data from these three setups present a cohesive picture of the volatility of the SOA formed in the dark from the three biogenic precursors. Under our experimental conditions, the SOA formed from NO3 + α-pinene was generally more volatile than SOA from α-pinene ozonolysis, while the NO3 oxidation of isoprene produced similar although slightly less volatile SOA than α-pinene under our experimental conditions. β-Caryophyllene reactions with NO3 resulted in the least volatile species.

    Four different parameterizations for estimating the saturation vapor pressure of the oxidation products were tested for reproducing the observed evaporation in a kinetic modeling framework. Our results show that the SOA from nitrate oxidation of α-pinene or isoprene is dominated by low-volatility organic compounds (LVOCs) and semi-volatile organic compounds (SVOCs), while the corresponding SOA from β-caryophyllene consists primarily of extremely low-volatility organic compounds (ELVOCs) and LVOCs. The parameterizations yielded variable results in terms of reproducing the observed evaporation, and generally the comparisons pointed to a need for re-evaluating the treatment of the nitrate group in such parameterizations. Strategies for improving the predictive power of the volatility parameterizations, particularly in relation to the contribution from the nitrate group, are discussed.

  • 41.
    Graham, Emelie Linnéa
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Wideqvist, Ulla
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Hennig, Tabea
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Physical and chemical properties of aerosol particles and cloud residuals on Mt. angstrom reskutan in Central Sweden during summer 20142020In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 72, no 1, article id 1445379Article in journal (Refereed)
    Abstract [en]

    The size distribution, volatility and hygroscopicity of ambient aerosols and cloud residuals were measured with a differential mobility particle sizer (DMPS) and a volatility-hygroscopicity tandem differential mobility analyser (VHTDMA) coupled to a counterflow virtual impactor (CVI) inlet during the Cloud and Aerosol Experiment at Are (CAEsAR) campaign at Mt. Areskutan during summer 2014. The chemical composition of particulate matter (PM) and cloud water were analysed offline using thermo-optical OC/EC analysis and ion chromatography. The importance of aerosol particle size for cloud droplet activation and subsequent particle scavenging was clearly visible in the measured size distributions. Cloud residuals were shifted towards larger sizes compared to ambient aerosol, and the cloud events were followed by a size distribution dominated by smaller particles. Organics dominated both PM (62% organic mass fraction) and cloud water (63% organic mass fraction) composition. The volatility and hygroscopicity of the ambient aerosols were representative of homogeneous aged aerosol with contributions from biogenic secondary organics, with median volume fraction remaining (VFR) of 0.04-0.05, and median hygroscopicity parameter kappa of 0.16-0.24 for 100-300 nm particles. The corresponding VFR and kappa for the cloud residuals were 0.03-0.04 and 0.18-0.20. The chemical composition, hygroscopicity and volatility measurements thus showed no major differences between the ambient aerosol particles and cloud residuals. The VFR and kappa values predicted based on the chemical composition measurements agreed well with the VHTDMA measurements, indicating the bulk chemical composition to be a reasonable approximation throughout the size distribution. There were indications, however, of some more subtle changes in time scales not achievable by the offline chemical analysis applied here. Further, online observations of aerosol and cloud residual chemical composition are therefore warranted.

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  • 42.
    Gramlich, Yvette
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science. Bolin Centre for Climate Research.
    Siegel, Karolina
    Stockholm University, Faculty of Science, Department of Meteorology . Stockholm University, Faculty of Science, Department of Environmental Science. Bolin Centre for Climate Research.
    Haslett, Sophie
    Stockholm University, Faculty of Science, Department of Environmental Science. Bolin Centre for Climate Research.
    Freitas, Gabriel
    Stockholm University, Faculty of Science, Department of Environmental Science. Bolin Centre for Climate Research.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science. Bolin Centre for Climate Research.
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Environmental Science. Bolin Centre for Climate Research.
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science. Bolin Centre for Climate Research.
    In-situ molecular characterization of Arctic cloud residuals using FIGAERO-CIMS behind a ground-based counterflow virtual impactorManuscript (preprint) (Other academic)
    Abstract [en]

    The role organic aerosols play in Arctic cloud formation is still poorly understood. In this study we address this issue by in-situ observations of cloud residuals at the Zeppelin Observatory in Ny-Ålesund, Svalbard (approx. 480 m a. s. l.) The measurements were part of the one-year long Ny-Ålesund Aerosol and Cloud Experiment 2019-2020 (NASCENT). We deployed a Filter Inlet for Gases and AEROsols coupled to a Chemical Ionization Mass Spectrometer (FIGAERO-CIMS) behind a ground-based counterflow virtual impactor (GCVI) to obtain the chemical composition of cloud residuals at molecular level. Between December 2019 and December 2020, we observed in total 14 cloud events. The compositions of the cloud residuals show a clear signal of methanesulfonic acid in spring, summer and autumn, but not in the winter, suggesting a marine contribution to the aerosol population activating into cloud droplets. In addition, we observe organic compounds in the cloud residuals throughout the entire year, with elevated fractions in summer. The biomass burning tracer levoglucosan was found in the cloud residuals as well, with highest contributions to the cloud residual mass at the end of summer (end of June until mid-September). Inorganic compounds (sulfuric acid and nitric acid) were also detected in the cloud residuals. Sulfuric acid concentrations were especially elevated in two of the cloud residuals (May 21 and September 12, 2020), but followed the overall pattern of the levels of MSA in the cloud residuals during the rest of the year. Overall, the results show the contribution of a marine contribution to the aerosol population able to form clouds in the Arctic environment during the summer months.

  • 43.
    Gramlich, Yvette
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Siegel, Karolina
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, Department of Meteorology . Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Haslett, Sophie L.
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Pereira Freitas, Gabriel
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Mohr, Claudia
    Stockholm University, Faculty of Science, Department of Environmental Science. Stockholm University, Faculty of Science, The Bolin Centre for Climate Research (together with KTH & SMHI).
    Revealing the chemical characteristics of Arctic low-level cloud residuals – in situ observations from a mountain site2023In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 23, no 12, p. 6813-6834Article in journal (Refereed)
    Abstract [en]

    The role aerosol chemical composition plays in Arctic low-level cloud formation is still poorly understood. In this study we address this issue by combining in situ observations of the chemical characteristics of cloud residuals (dried liquid cloud droplets or ice crystals) and aerosol particles from the Zeppelin Observatory in Ny-Ålesund, Svalbard (approx. 480 m a.s.l.). These measurements were part of the 1-year-long Ny-Ålesund Aerosol and Cloud Experiment 2019–2020 (NASCENT). To obtain the chemical composition of cloud residuals at molecular level, we deployed a Filter Inlet for Gases and AEROsols coupled to a Chemical Ionization Mass Spectrometer (FIGAERO-CIMS) with iodide as the reagent ion behind a ground-based counterflow virtual impactor (GCVI). The station was enshrouded in clouds roughly 15 % of the time during NASCENT, out of which we analyzed 14 cloud events between December 2019 and December 2020. During the entire year, the composition of the cloud residuals shows contributions from oxygenated organic compounds, including organonitrates, and traces of the biomass burning tracer levoglucosan. In summer, methanesulfonic acid (MSA), an oxidation product of dimethyl sulfide (DMS), shows large contributions to the sampled mass, indicating marine natural sources of cloud condensation nuclei (CCN) and ice nucleating particle (INP) mass during the sunlit part of the year. In addition, we also find contributions of the inorganic acids nitric acid and sulfuric acid, with outstanding high absolute signals of sulfuric acid in one cloud residual sample in spring and one in late summer (21 May and 12 September 2020), probably caused by high anthropogenic sulfur emissions near the Barents Sea and Kara Sea. During one particular cloud event, on 18 May 2020, the air mass origin did not change before, during, or after the cloud. We therefore chose it as a case study to investigate cloud impact on aerosol physicochemical properties. We show that the overall chemical composition of the organic aerosol particles was similar before, during, and after the cloud, indicating that the particles had already undergone one or several cycles of cloud processing before being measured as residuals at the Zeppelin Observatory and/or that, on the timescales of the observed cloud event, cloud processing of the organic fraction can be neglected. Meanwhile, there were on average fewer particles but relatively more in the accumulation mode after the cloud. Comparing the signals of sulfur-containing compounds of cloud residuals with aerosols during cloud-free conditions, we find that sulfuric acid had a higher relative contribution to the cloud residuals than to aerosols during cloud-free conditions, but we did not observe an increase in particulate MSA due to the cloud. Overall, the chemical composition, especially of the organic fraction of the Arctic cloud residuals, reflected the overall composition of the general aerosol population well. Our results thus suggest that most aerosols can serve as seeds for low-level clouds in the Arctic.

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  • 44.
    Grythe, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Norwegian Institute for Air Research (NILU), Norway; Finnish Meteorological Institute (FMI), Finland.
    Kristiansen, Nina I.
    Groot Zwaaftink, Christine D.
    Eckhardt, Sabine
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). University of Helsinki, Finland.
    Stohl, Andreas
    A new aerosol wet removal scheme for the Lagrangian particle model FLEXPART2017In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 10, no 4, p. 1447-1466Article in journal (Refereed)
    Abstract [en]

    A new and more physically based treatment of how removal by precipitation is calculated by FLEXPART is introduced, to take into account more aspects of aerosol diversity. Also new, is the definition of clouds and cloud properties. Results from simulations show good agreement with observed atmospheric concentrations for distinctly different aerosols. Atmospheric lifetimes were found to vary from a few hours (large aerosol particles) up to a month (small non-soluble).

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  • 45.
    Grythe, Henrik
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Norwegian Institute for Air Research (NILU), Norway; Finnish Meteorological Institute (FMI), Finland.
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). University of Helsinki, Finland.
    Quinn, P.
    Stohl, A.
    A review of sea-spray aerosol source functions using a large global set of sea salt aerosol concentration measurements2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 3, p. 1277-1297Article in journal (Refereed)
    Abstract [en]

    Sea-spray aerosols (SSA) are an important part of the climate system because of their effects on the global radiative budget - both directly as scatterers and absorbers of solar and terrestrial radiation, and indirectly as cloud condensation nuclei (CCN) influencing cloud formation, lifetime, and precipitation. In terms of their global mass, SSA have the largest uncertainty of all aerosols. In this study we review 21 SSA source functions from the literature, several of which are used in current climate models. In addition, we propose a new function. Even excluding outliers, the global annual SSA mass produced spans roughly 3-70 Pg yr(-1) for the different source functions, for particles with dry diameter D-p < 10 mu m, with relatively little interannual variability for a given function. The FLEXPART Lagrangian particle dispersion model was run in backward mode for a large global set of observed SSA concentrations, comprised of several station networks and ship cruise measurement campaigns. FLEXPART backward calculations produce gridded emission sensitivity fields, which can subsequently be multiplied with gridded SSA production fluxes in order to obtain modeled SSA concentrations. This allowed us to efficiently and simultaneously evaluate all 21 source functions against the measurements. Another advantage of this method is that source-region information on wind speed and sea surface temperatures (SSTs) could be stored and used for improving the SSA source function parameterizations. The best source functions reproduced as much as 70% of the observed SSA concentration variability at several stations, which is comparable with state of the art aerosol models. The main driver of SSA production is wind, and we found that the best fit to the observation data could be obtained when the SSA production is proportional to U-10(3.5), where U-10 is the source region averaged 10m wind speed. A strong influence of SST on SSA production, with higher temperatures leading to higher production, could be detected as well, although the underlying physical mechanisms of the SST influence remains unclear. Our new source function with wind speed and temperature dependence gives a global SSA production for particles smaller than D-p < 10 mu m of 9 Pg yr(-1), and is the best fit to the observed concentrations.

  • 46. Hamburger, T.
    et al.
    McMeeking, G.
    Minikin, A.
    Birmili, W.
    Dall'Osto, M.
    O'Dowd, C.
    Flentje, H.
    Henzing, B.
    Junninen, H.
    Kristensson, A.
    de Leeuw, G.
    Stohl, A.
    Burkhart, J. F.
    Coe, H.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Petzold, A.
    Overview of the synoptic and pollution situation over Europe during the EUCAARI-LONGREX field campaign2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 3, p. 1065-1082Article in journal (Refereed)
    Abstract [en]

    In May 2008 the EUCAARI-LONGREX aircraft field campaign was conducted within the EUCAARI intensive observational period. The campaign aimed at studying the distribution and evolution of air mass properties on a continental scale. Airborne aerosol and trace gas measurements were performed aboard the German DLR Falcon 20 and the British FAAM BAe-146 aircraft. This paper outlines the meteorological situation over Europe during May 2008 and the temporal and spatial evolution of predominantly anthropogenic particulate pollution inside the boundary layer and the free troposphere. Time series data of six selected ground stations are used to discuss continuous measurements besides the single flights. The observations encompass total and accumulation mode particle number concentration (0.1–0.8 μm) and black carbon mass concentration as well as several meteorological parameters. Vertical profiles of total aerosol number concentration up to 10 km are compared to vertical profiles probed during previous studies.

    During the first half of May 2008 an anticyclonic blocking event dominated the weather over Central Europe. It led to increased pollutant concentrations within the centre of the high pressure inside the boundary layer. Due to long-range transport the accumulated pollution was partly advected towards Western and Northern Europe. The measured aerosol number concentrations over Central Europe showed in the boundary layer high values up to 14 000 cm−3 for particles in diameter larger 10 nm and 2300 cm−3 for accumulation mode particles during the high pressure period, whereas the middle free troposphere showed rather low concentrations of particulates. Thus a strong negative gradient of aerosol concentrations between the well mixed boundary layer and the clean middle troposphere occurred.

  • 47.
    Hamburger, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Matisans, Modris
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Calderon, S.
    Hoffmann, P.
    Hochschild, G.
    Gross, J.
    Schmeissner, T.
    Wiedensohler, A.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Long-term in situ observations of biomass burning aerosol at a high altitude station in Venezuela - sources, impacts and interannual variability2013In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, no 19, p. 9837-9853Article in journal (Refereed)
    Abstract [en]

    First long-term observations of South American biomass burning aerosol within the tropical lower free troposphere are presented. The observations were conducted between 2007 and 2009 at a high altitude station (4765 m a.s.l.) on the Pico Espejo, Venezuela. Sub-micron particle volume, number concentrations of primary particles and particle absorption were observed. Orographic lifting and shallow convection leads to a distinct diurnal cycle at the station. It enables measurements within the lower free troposphere during night-time and observations of boundary layer air masses during daytime and at their transitional regions. The seasonal cycle is defined by a wet rainy season and a dry biomass burning season. The particle load of biomass burning aerosol is dominated by fires in the Venezuelan savannah. Increases of aerosol concentrations could not be linked to long-range transport of biomass burning plumes from the Amazon basin or Africa due to effective wet scavenging of particles. Highest particle concentrations were observed within boundary layer air masses during the dry season. Ambient sub-micron particle volume reached 1.4 +/- 1.3 mu m(3) cm(-3), refractory particle number concentrations (at 300 degrees C) 510+/-420 cm(-3) and the absorption coefficient 0.91+/-1.2 Mm(-1). The respective concentrations were lowest within the lower free troposphere during the wet season and averaged at 0.19+/-0.25 mu m(3) cm-3, 150+/-94 cm(-3) and 0.15+/-0.26 Mm(-1). A decrease of particle concentrations during the dry seasons from 2007-2009 could be connected to a decrease in fire activity in the wider region of Venezuela using MODIS satellite observations. The variability of biomass burning is most likely linked to the El Nino-Southern Oscillation (ENSO). Low biomass burning activity in the Venezuelan savannah was observed to follow La Nina conditions, high biomass burning activity followed El Nino conditions.

  • 48.
    Hamburger, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    McMeeking, G.
    Minikin, A.
    Petzold, A.
    Coe, H.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Airborne observations of aerosol microphysical properties and particle ageing processes in the troposphere above Europe2012In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, no 23, p. 11533-11554Article in journal (Refereed)
    Abstract [en]

    In-situ measurements of aerosol microphysical properties were performed in May 2008 during the EUCAARI-LONGREX campaign. Two aircraft, the FAAM BAe-146 and DLR Falcon 20, operated from Oberpfaffenhofen, Germany. A comprehensive data set was obtained comprising the wider region of Europe north of the Alps throughout the whole tropospheric column. Prevailing stable synoptic conditions enabled measurements of accumulating emissions inside the continental boundary layer reaching a maximum total number concentration of 19 000 particles cm(-3) stp. Ultra-fine particles as indicators for nucleation events were observed within the boundary layer during high pressure conditions and after updraft of emissions induced by frontal passages above 8 km altitude in the upper free troposphere. Aerosol ageing processes during air mass transport are analysed using trajectory analysis. The ratio of particles containing a non-volatile core (250 degrees C) to the total aerosol number concentration was observed to increase within the first 12 to 48 h from the particle source from 50 to 85% due to coagulation. Aged aerosol also features an increased fraction of accumulation mode particles of approximately 40% of the total number concentration. The presented analysis provides an extensive data set of tropospheric aerosol microphysical properties on a continental scale which can be used for atmospheric aerosol models and comparisons of satellite retrievals.

  • 49. Hansen, A. M. K.
    et al.
    Kristensen, K.
    Nguyen, Q. T.
    Zare, A.
    Cozzi, F.
    Nøjgaard, J. K.
    Skov, H.
    Brandt, J.
    Christensen, J. H.
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). University of Helsinki, Finland.
    Glasius, M.
    Organosulfates and organic acids in Arctic aerosols: speciation, annual variation and concentration levels2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 15, p. 7807-7823Article in journal (Refereed)
    Abstract [en]

    Sources, composition and occurrence of secondary organic aerosols in the Arctic were investigated at Zeppelin Mountain, Svalbard, and Station Nord, northeastern Greenland, during the full annual cycle of 2008 and 2010, respectively. Speciation of organic acids, organosulfates and nitrooxy organosulfates - from both anthropogenic and biogenic precursors were in focus. A total of 11 organic acids (terpenylic acid, benzoic acid, phthalic acid, pinic acid, suberic acid, azelaic acid, adipic acid, pimelic acid, pinonic acid, diaterpenylic acid acetate and 3-methyl-1,2,3-butanetricarboxylic acid), 12 organosulfates and 1 nitrooxy organosulfate were identified in aerosol samples from the two sites using a high-performance liquid chromatograph (HPLC) coupled to a quadrupole Time-of-Flight mass spectrometer. At Station Nord, compound concentrations followed a distinct annual pattern, where high mean concentrations of organosulfates (47 +/- 14 ng m(-3)) and organic acids (11.5 +/- 4 ng m(-3)) were observed in January, February and March, contrary to considerably lower mean concentrations of organosulfates (2 +/- 3 ng m(3-)) and organic acids (2.2 +/- 1 ng m(-3)) observed during the rest of the year. At Zeppelin Mountain, organosulfate and organic acid concentrations remained relatively constant during most of the year at a mean concentration of 15 +/- 4 ng m(-3) and 3.9 +/- 1 ng m(-3), respectively. However during four weeks of spring, remarkably higher concentrations of total organosulfates (23-36 ng m(-3)) and total organic acids (7-10 ngm(-3)) were observed. Elevated organosulfate and organic acid concentrations coincided with the Arctic haze period at both stations, where northern Eurasia was identified as the main source region. Air mass transport from northern Eurasia to Zeppelin Mountain was associated with a 100% increase in the number of detected organosulfate species compared with periods of air mass transport from the Arctic Ocean, Scandinavia and Greenland. The results from this study suggested that the presence of organic acids and organosulfates at Station Nord was mainly due to long-range transport, whereas indications of local sources were found for some compounds at Zeppelin Mountain. Furthermore, organosulfates contributed significantly to organic matter throughout the year at Zeppelin Mountain (annual mean of 13 +/- 8 %) and during Arctic haze at Station Nord (7 +/- 2 %), suggesting organosulfates to be important compounds in Arctic aerosols.

  • 50.
    Hansson, Hans-Christen
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science. Navarino Environmental Observatory, Greece.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science. Navarino Environmental Observatory, Greece.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science. Navarino Environmental Observatory, Greece.
    Freud, Eyal
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Kalivitis, Nikos
    Hennig, Tabea
    Stockholm University, Faculty of Science, Department of Environmental Science.
    Maneas, Giorgos
    Stockholm University, Faculty of Science, Department of Physical Geography. Navarino Environmental Observatory, Greece.
    Gerasopoulos, Evangelos
    The Atmospheric Aerosol over Western Greece-Six Years of Aerosol Observations at the Navarino Environmental Observatory2021In: Atmosphere, ISSN 2073-4433, E-ISSN 2073-4433, Vol. 12, no 4, article id 445Article in journal (Refereed)
    Abstract [en]

    The Eastern Mediterranean is a highly populated area with air quality problems. It is also where climate change is already noticed by higher temperatures and s changing precipitation pattern. The anthropogenic aerosol affects health and changing concentrations and properties of the atmospheric aerosol affect radiation balance and clouds. Continuous long-term observations are essential in assessing the influence of anthropogenic aerosols on climate and health. We present six years of observations from Navarino Environmental Observatory (NEO), a new station located at the south west tip of Peloponnese, Greece. The two sites at NEO, were evaluated to show the influence of the local meteorology and to assess the general background aerosol possible. It was found that the background aerosol was originated from aged European aerosols and was strongly influenced by biomass burning, fossil fuel combustion, and industry. When subsiding into the boundary layer, local sources contributed in the air masses moving south. Mesoscale meteorology determined the diurnal variation of aerosol properties such as mass and number by means of typical sea breeze circulation, giving rise to pronounced morning and evening peaks in pollutant levels. While synoptic scale meteorology, mainly large-scale air mass transport and precipitation, strongly influenced the seasonality of the aerosol properties.

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