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  • 1.
    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)
  • 2.
    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.

  • 3.
    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)
  • 4.
    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.

  • 5.
    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.

  • 6. 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.

  • 7.
    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)
  • 8.
    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, ISSN 2041-1723, 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.

  • 9.
    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.

  • 10. 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, ISSN 2045-2322, 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.

  • 11.
    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.

  • 12.
    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.

  • 13.
    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.

  • 14. 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.

  • 15. 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.

  • 16.
    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.

  • 17.
    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.

  • 18.
    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.

  • 19.
    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)
  • 20.
    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).

  • 21.
    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.

  • 22. 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.

  • 23.
    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.

  • 24.
    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.

  • 25. 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.

  • 26.
    Hultin, Kim
    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).
    Pinhassi, Jarone
    Gomez-Consarnau, Laura
    Mårtensson, Monica
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hagström, Åke
    Nilsson, Douglas
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Aerosol and bacterial emissions from Baltic Seawater2011In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 99, no 1, p. 1-14Article in journal (Refereed)
    Abstract [en]

    Factors influencing the production of primary marine aerosol are of great importance to better understand the marine aerosols' impact on our climate. Bubble-bursting from whitecaps is considered the most effective mechanism for sea spray production, and a way of sea–air transfer for some bacterial species.

    Two coastal sites in the Baltic Sea were used to investigate aerosol and bacterial emissions from the bubble-bursting process by letting a jet of water hit a water surface within an experimental tank, mimicking the actions of breaking waves.

    The aerosol size distribution spectra from the two sites were similar and conservative in shape where the modes were centered at about 200 nm dry diameter. We found a distinct decrease in bubbled aerosol production with increasing water temperature. A clear diurnal cycle in bubbled aerosol production was observed, anticorrelated with both water temperature and dissolved oxygen, which to our knowledge has never been shown before. A link between decreasing aerosol production in daytime and phytoplankton activity is likely to be an important factor. Colony-forming bacteria were transferred to the atmosphere via the bubble-bursting process, with a linear relationship to their seawater concentration.

  • 27.
    Hultin, Kim
    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).
    Ehn, Mikael
    Hagström, Åke
    de Leeuw, Gerrit
    In situ laboratory sea spray production during the Marine Aerosol Production 2006 cruise on the northeastern Atlantic Ocean2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, p. D06201-Article in journal (Refereed)
    Abstract [en]

    Bubbles bursting from whitecaps are considered to be the most effective mechanism for particulate matter to be ejected into the atmosphere from the Earth's oceans. To realistically predict the climate effect of marine aerosols, global climate models require process-based understanding of particle formation from bubble bursting. During a cruise on the highly biologically active waters of the northeastern Atlantic Ocean in the summer of 2006, the submicrometer primary marine aerosol produced by a jet of seawater impinging on a seawater surface was investigated. The produced aerosol size spectra were centered on 200 nm in dry diameter and were conservative in shape throughout the cruise. The aerosol number production was negatively correlated with dissolved oxygen (DO) in the water (r < −0.6 for particles of dry diameter Dp > 200 nm). An increased surfactant concentration as a result of biological activity affecting the oxygen saturation is thought to diminish the particle production. The lack of influence of chlorophyll on aerosol production indicates that hydrocarbons produced directly by the photosynthesis are not essential for sea spray production. The upward mixing of deeper ocean water as a result of higher wind speed appears to affect the aerosol particle production, making wind speed influence aerosol production in more ways than by increasing the amount of whitecaps. The bubble spectra produced by the jet of seawater was representative of breaking waves at open sea, and the particle number production was positively correlated with increasing bubble number concentration with a peak production of 40–50 particles per bubble.

  • 28.
    Hultin, Kim
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Zábori, Julia
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ekman, Annica
    Stockholm University, Faculty of Science, Department of Meteorology .
    Mårtensson, Monica
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Nilsson, Douglas
    Volatility properties and mixing state of submicron primary marine aerosol from Arctic seawater near SvalbardManuscript (preprint) (Other academic)
  • 29. Kulmala, M.
    et al.
    Asmi, A.
    Lappalainen, H. K.
    Baltensperger, U.
    Brenguier, J. -L
    Facchini, M. C.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hov, O.
    O'Dowd, C. D.
    Poeschl, U.
    Wiedensohler, A.
    Boers, R.
    Boucher, O.
    de Leeuw, G.
    van der Gon, H. A. C. Denier
    Feichter, J.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Laj, P.
    Lihavainen, H.
    Lohmann, U.
    McFiggans, G.
    Mentel, T.
    Pilinis, C.
    Riipinen, I.
    Schulz, M.
    Stohl, A.
    Swietlicki, E.
    Vignati, E.
    Alves, C.
    Amann, M.
    Ammann, M.
    Arabas, S.
    Artaxo, P.
    Baars, H.
    Beddows, D. C. S.
    Bergstrom, R.
    Beukes, J. P.
    Bilde, M.
    Burkhart, J. F.
    Canonaco, F.
    Clegg, S. L.
    Coe, H.
    Crumeyrolle, S.
    D'Anna, B.
    Decesari, S.
    Gilardoni, S.
    Fischer, M.
    Fjaeraa, A. M.
    Fountoukis, C.
    George, C.
    Gomes, L.
    Halloran, P.
    Hamburger, T.
    Harrison, R. M.
    Herrmann, H.
    Hoffmann, T.
    Hoose, C.
    Hu, M.
    Hyvarinen, A.
    Horrak, U.
    Iinuma, Y.
    Iversen, T.
    Josipovic, M.
    Kanakidou, M.
    Kiendler-Scharr, A.
    Kirkevag, A.
    Kiss, G.
    Klimont, Z.
    Kolmonen, P.
    Komppula, M.
    Kristjansson, J. -E
    Laakso, L.
    Laaksonen, A.
    Labonnote, L.
    Lanz, V. A.
    Lehtinen, K. E. J.
    Rizzo, L. V.
    Makkonen, R.
    Manninen, H. E.
    McMeeking, G.
    Merikanto, J.
    Minikin, A.
    Mirme, S.
    Morgan, W. T.
    Nemitz, E.
    O'Donnell, D.
    Panwar, T. S.
    Pawlowska, H.
    Petzold, A.
    Pienaar, J. J.
    Pio, C.
    Plass-Duelmer, C.
    Prevot, A. S. H.
    Pryor, S.
    Reddington, C. L.
    Roberts, G.
    Rosenfeld, D.
    Schwarz, J.
    Seland, O.
    Sellegri, K.
    Shen, X. J.
    Shiraiwa, M.
    Siebert, H.
    Sierau, B.
    Simpson, D.
    Sun, J. Y.
    Topping, D.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Vaattovaara, P.
    Vakkari, V.
    Veefkind, J. P.
    Visschedijk, A.
    Vuollekoski, H.
    Vuolo, R.
    Wehner, B.
    Wildt, J.
    Woodward, S.
    Worsnop, D. R.
    van Zadelhoff, G. -J
    Zardini, A. A.
    Zhang, K.
    van Zyl, P. G.
    Kerminen, V. -M
    Carslaw, K. S.
    Pandis, S. N.
    General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) - integrating aerosol research from nano to global scales2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 24, p. 13061-13143Article in journal (Refereed)
    Abstract [en]

    In this paper we describe and summarize the main achievements of the European Aerosol Cloud Climate and Air Quality Interactions project (EUCAARI). EUCAARI started on 1 January 2007 and ended on 31 December 2010 leaving a rich legacy including: (a) a comprehensive database with a year of observations of the physical, chemical and optical properties of aerosol particles over Europe, (b) comprehensive aerosol measurements in four developing countries, (c) a database of airborne measurements of aerosols and clouds over Europe during May 2008, (d) comprehensive modeling tools to study aerosol processes fron nano to global scale and their effects on climate and air quality. In addition a new Pan-European aerosol emissions inventory was developed and evaluated, a new cluster spectrometer was built and tested in the field and several new aerosol parameterizations and computations modules for chemical transport and global climate models were developed and evaluated. These achievements and related studies have substantially improved our understanding and reduced the uncertainties of aerosol radiative forcing and air quality-climate interactions. The EUCAARI results can be utilized in European and global environmental policy to assess the aerosol impacts and the corresponding abatement strategies.

  • 30. Kulmala, M.
    et al.
    Kerminen, V.-M.
    Laaksonen, A.
    Riipinen, I.
    Sipilä, M.
    Ruuskanen, T.M.
    Sogacheva, L.
    Hari, P.
    Bäck, J.
    Lehtinen, K.E.J.
    Viisanen, Y.
    Bilde, M.
    Svenningsson, B.
    Lazaridis, M.
    Torseth, K.
    Tunsved, P.
    Nilsson, D
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Pryor, S.
    Sorensen, L.-L.
    Hörrak, U.
    Winkler, P.M.
    Swietlicki, E.
    Riekkola, M.-L.
    Krejci, R
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hoyle, C.
    Hov, G.
    Myhre, G.
    Hansson, H
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Overview of the BACCI (Biosphere-Atmosphere-Cloud-Climate Interactions) studies2008In: Tellus B, Vol. 6, no 3, p. 300-317Article in journal (Refereed)
  • 31. Kulmala, Markku
    et al.
    Nieminen, Tuomo
    Nikandrova, Anna
    Lehtipalo, Katrianne
    Manninen, Hanna E.
    Kajos, Maija K.
    Kolari, Pasi
    Lauri, Antti
    Petaja, Tuukka
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). University of Helsinki, Finland.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Swietlicki, Erik
    Lindroth, Anders
    Christensen, Torben R.
    Arneth, Almut
    Hari, Pertti
    Bäck, Jaana
    Vesala, Timo
    Kerminen, Veli-Matti
    CO2-induced terrestrial climate feedback mechanism: From carbon sink to aerosol source and back2014In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 19, p. 122-131Article in journal (Refereed)
    Abstract [en]

    Feedbacks mechanisms are essential components of our climate system, as they either increase or decrease changes in climate-related quantities in the presence of external forcings. In this work, we provide the first quantitative estimate regarding the terrestrial climate feedback loop connecting the increasing atmospheric carbon dioxide concentration, changes in gross primary production (GPP) associated with the carbon uptake, organic aerosol formation in the atmosphere, and transfer of both diffuse and global radiation. Our approach was to combine process-level understanding with comprehensive, long-term field measurement data set collected from a boreal forest site in southern Finland. Our best estimate of the gain in GPP resulting from the feedback is 1.3 (range 1.02-1.5), which is larger than the gains of the few atmospheric chemistry-climate feedbacks estimated using large-scale models. Our analysis demonstrates the power of using comprehensive field measurements in investigating the complicated couplings between the biosphere and atmosphere on one hand, and the need for complementary approaches relying on the combination of field data, satellite observations model simulations on the other hand.

  • 32. Lupi, Angelo
    et al.
    Busetto, Maurizio
    Becagli, Silvia
    Giardi, Fabio
    Lanconelli, Christian
    Mazzola, Mauro
    Udisti, Roberto
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Hennig, Tabea
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Petkov, Boyan
    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.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Viola, Angelo Pietro
    Vitale, Vito
    Multi-seasonal ultrafine aerosol particle number concentration measurements at the Gruvebadet observatory, Ny-lesund, Svalbard Islands2016In: Rendiconti lincei scienze fisiche e naturali, ISSN 2037-4631, Vol. 27, p. 59-71Article in journal (Refereed)
    Abstract [en]

    The object of this study was to investigate the different modal behavior of ultrafine aerosol particles collected at the Gruvebadet observatory located in Ny-lesund (Svalbard Islands, 78A degrees 55'N, 11A degrees 56'E). Aerosol particle size distribution was measured in the size range from 10 to 470 nm typically from the beginning of spring to the beginning of fall during four (non-consecutive) years (2010, 2011, 2013 and 2014). The median concentration for the whole period taken into account was 214 particles cm(-3), oscillating between the median maximum in July with a concentration of 257 particles cm(-3) and a median minimum in April with 197 particles cm(-3). The median total number concentration did not present a well-defined seasonal behavior, as shown by contrast looking at the sub/modal number concentration, where distinct trends appeared in the predominant accumulation concentration recorded during April/May and the preponderant concentration of Aitken particles during the summer months. Lastly, the short side-by-side spring 2013 campaign performed at the Zeppelin observatory with a differential mobility particle sizer was characterized by an aerosol concentration mean steady difference between the two instruments of around 14 %, thereby supporting the reliability of the device located at Gruvebadet.

  • 33.
    Matisans, Modris
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hamburger, Thomas
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Manninen, Hanna E.
    Backman, John
    Rizzo, Luciana
    Artaxo, Paulo
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Swietlicki, Erik
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Kulmala, Markku
    New Aerosol Particle Formation in Amazonia2013In: NUCLEATION AND ATMOSPHERIC AEROSOLS, American Institute of Physics (AIP), 2013, p. 571-574Conference paper (Refereed)
    Abstract [en]

    Particle nucleation in Amazonia has been an enigma throughout decades of active scrutiny of natural nucleation processes; however, measurements have so far been thought to fail capturing an actual new particle formation (NPF) event. In this study we have analyzed latest measurements of ultra-fine particle size distributions alongside with air ion spectra and revealed a diurnal pattern of ultra-fine particle apparent growth. The revealed growth pattern is preceded by diurnal precipitation probability maxima, and simultaneous abundant ion production as detected by Neutral cluster and Air Ion Spectrometer (NAIS) data. Thus, we claim that by implementing statistical analysis of scanning mobility particle sizer (SMPS) data and combining with independent observations from Neutral cluster and Air Ion Spectrometer (NAIS) we can observe a consistent signal of NPF events in Amazonia.

  • 34. McMeeking, G. R.
    et al.
    Hamburger, T.
    Liu, D.
    Flynn, M.
    Morgan, W. T.
    Northway, M.
    Highwood, E. J.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Allan, J. D.
    Minikin, A.
    Coe, H.
    Black carbon measurements in the boundary layer over western and northern Europe2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 19, p. 9393-9414Article in journal (Refereed)
    Abstract [en]

    Europe is a densely populated region that is a significant global source of black carbon (BC) aerosol, but there is a lack of information regarding the physical properties and spatial/vertical distribution of rBC in the region. We present the first aircraft observations of sub-micron refractory BC (rBC) aerosol concentrations and physical properties measured by a single particle soot photometer (SP2) in the lower troposphere over Europe. The observations spanned a region roughly bounded by 50 degrees to 60 degrees N and from 15 degrees W to 30 degrees E. The measurements, made between April and September 2008, showed that average rBC mass concentrations ranged from about 300 ng m(-3) near urban areas to approximately 50 ng m(-3) in remote continental regions, lower than previous surface-based measurements. rBC represented between 0.5 and 3% of the sub-micron aerosol mass. Black carbon mass size distributions were log-normally distributed and peaked at approximately 180 nm, but shifted to smaller diameters (similar to 160 nm) near source regions. rBC was correlated with carbon monoxide (CO) but had different ratios to CO depending on location and air mass. Light absorption coefficients were measured by particle soot absorption photometers on two separate aircraft and showed similar geographic patterns to rBC mass measured by the SP2. We summarize the rBC and light absorption measurements as a function of longitude and air mass age and also provide profiles of rBC mass concentrations and size distribution statistics. Our results will help evaluate model-predicted regional rBC concentrations and properties and determine regional and global climate impacts from rBC due to atmospheric heating and surface dimming.

  • 35. Morgan, W. T.
    et al.
    Allan, J. D.
    Bower, K. N.
    Esselborn, M.
    Harris, B.
    Henzing, J. S.
    Highwood, E. J.
    Kiendler-Scharr, A.
    McMeeking, G. R.
    Mensah, A. A.
    Northway, M. J.
    Osborne, S.
    Williams, P. I.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Coe, H.
    Enhancement of the aerosol direct radiative effect by semi-volatile aerosol components: airborne measurements in North-Western Europe2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 17, p. 8151-8171Article in journal (Refereed)
    Abstract [en]

    A case study of atmospheric aerosol measurements exploring the impact of the vertical distribution of aerosol chemical composition upon the radiative budget in North-Western Europe is presented. Sub-micron aerosol chemical composition was measured by an Aerodyne Aerosol Mass Spectrometer (AMS) on both an airborne platform and a ground-based site at Cabauw in the Netherlands. The examined period in May 2008 was characterised by enhanced pollution loadings in North-Western Europe and was dominated by ammonium nitrate and Organic Matter (OM). Both ammonium nitrate and OM were observed to increase with altitude in the atmospheric boundary layer. This is primarily attributed to partitioning of semi-volatile gas phase species to the particle phase at reduced temperature and enhanced relative humidity. Increased ammonium nitrate concentrations in particular were found to strongly increase the ambient scattering potential of the aerosol burden, which was a consequence of the large amount of associated water as well as the enhanced mass. During particularly polluted conditions, increases in aerosol optical depth of 50-100% were estimated to occur due to the observed increase in secondary aerosol mass and associated water uptake. Furthermore, the single scattering albedo was also shown to increase with height in the boundary layer. These enhancements combined to increase the negative direct aerosol radiative forcing by close to a factor of two at the median percentile level. Such increases have major ramifications for regional climate predictions as semi-volatile components are often not included in aerosol models. The results presented here provide an ideal opportunity to test regional and global representations of both the aerosol vertical distribution and subsequent impacts in North-Western Europe. North-Western Europe can be viewed as an analogue for the possible future air quality over other polluted regions of the Northern Hemisphere, where substantial reductions in sulphur dioxide emissions have yet to occur. Anticipated reductions in sulphur dioxide in polluted regions will result in an increase in the availability of ammonia to form ammonium nitrate as opposed to ammonium sulphate. This will be most important where intensive agricultural practises occur. Our observations over North-Western Europe, a region where sulphur dioxide emissions have already been reduced, indicate that failure to include the semi-volatile behaviour of ammonium nitrate will result in significant errors in predicted aerosol direct radiative forcing. Such errors will be particularly significant on regional scales.

  • 36. Morgan, W. T.
    et al.
    Allan, J. D.
    Bower, K. N.
    Highwood, E. J.
    Liu, D.
    McMeeking, G. R.
    Northway, M. J.
    Williams, P. I.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Coe, H.
    Airborne measurements of the spatial distribution of aerosol chemical composition across Europe and evolution of the organic fraction2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 8, p. 4065-4083Article in journal (Refereed)
    Abstract [en]

    The spatial distribution of aerosol chemical composition and the evolution of the Organic Aerosol (OA) fraction is investigated based upon airborne measurements of aerosol chemical composition in the planetary boundary layer across Europe. Sub-micron aerosol chemical composition was measured using a compact Time-of-Flight Aerosol Mass Spectrometer (cToF-AMS). A range of sampling conditions were evaluated, including relatively clean background conditions, polluted conditions in North-Western Europe and the near-field to far-field outflow from such conditions. Ammonium nitrate and OA were found to be the dominant chemical components of the sub-micron aerosol burden, with mass fractions ranging from 20-50% each. Ammonium nitrate was found to dominate in North-Western Europe during episodes of high pollution, reflecting the enhanced NOx and ammonia sources in this region. OA was ubiquitous across Europe and concentrations generally exceeded sulphate by 30-160%. A factor analysis of the OA burden was performed in order to probe the evolution across this large range of spatial and temporal scales. Two separate Oxygenated Organic Aerosol (OOA) components were identified; one representing an aged-OOA, termed Low Volatility-OOA and another representing fresher-OOA, termed Semi Volatile-OOA on the basis of their mass spectral similarity to previous studies. The factors derived from different flights were not chemically the same but rather reflect the range of OA composition sampled during a particular flight. Significant chemical processing of the OA was observed downwind of major sources in North-Western Europe, with the LV-OOA component becoming increasingly dominant as the distance from source and photochemical processing increased. The measurements suggest that the aging of OA can be viewed as a continuum, with a progression from a less oxidised, semi-volatile component to a highly oxidised, less-volatile component. Substantial amounts of pollution were observed far downwind of continental Europe, with OA and ammonium nitrate being the major constituents of the sub-micron aerosol burden. Such anthropogenically perturbed air masses can significantly perturb regional climate far downwind of major source regions.

  • 37.
    Nilsson, Douglas
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hultin, Kim
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mårtensson, Monica
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Rosman, Kai
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Baltic Sea Spray Emissions: in situ Eddy Covariance Fluxes v.s. Simulated Tank Sea SprayManuscript (preprint) (Other academic)
  • 38.
    Nozière, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    González, Nélida J. D.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Borg-Karlson, Anna-Karin
    Pei, Yuxin
    Redeby, Johan Pettersson
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Dommen, Josef
    Prevot, Andre S. H.
    Anthonsen, Thorleif
    Atmospheric chemistry in stereo: A new look at secondary organic aerosols from isoprene2011In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 38, p. L11807-Article in journal (Refereed)
    Abstract [en]

    Isoprene, a compound emitted by vegetation, could be a major contributor to secondary organic aerosols (SOA) in the atmosphere. The main evidence for this contribution were the 2-methylbutane-1,2,3,4-tetraols, or 2-methyltetrols (2-methylerythritol and 2-methylthreitol) present in ambient aerosols. In this work, the four stereoisomers of these tetraols were analyzed in aerosols from Aspvreten, Sweden. 2-C-methyl-D-erythritol was found in excess over its enantiomer in the Spring/Summer, by up to 29% in July. This clearly indicated some biological origins for this enantiomer, consistent with its well-documented production by plants and other living organisms. In addition, a minimum of 20 to 60% of the mass of racemic tetraols appeared from biological origin. Thus, the SOA mass produced by isoprene in the atmosphere is less than what indicated by the 2-methyltetrols in aerosols. Our results also demonstrate that stereochemical speciation can distinguish primary and secondary organic material in atmospheric aerosols.

  • 39. Oulehle, Filip
    et al.
    Evans, Christopher D.
    Hofmeister, Jenyk
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tahovska, Karolina
    Persson, Tryggve
    Cudlin, Pavel
    Hruska, Jakub
    Major changes in forest carbon and nitrogen cycling caused by declining sulphur deposition2011In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 17, no 10, p. 3115-3129Article in journal (Refereed)
    Abstract [en]

    Sulphur (S) and nitrogen (N) deposition are important drivers of the terrestrial carbon (C) and N cycling. We analyzed changes in C and N pools in soil and tree biomass at a highly acidified spruce site in the Czech Republic during a 15 year period. Total S deposition decreased from 5 to 1.1 g m(-2) yr(-1) between 1995 and 2009, whereas bulk N deposition did not change. Over the same period, C and N pools in the Oa horizon declined by 116 g C and 4.2 g N m(-2) yr(-1), a total decrease of 47% and 42%, respectively. This loss of C and N probably originated from organic matter (OM) that had accumulated during the period of high acid deposition when litter decomposition was suppressed. The loss of OM from the Oa horizon coincided with a substantial leaching (1.3 g N m(-2) yr(-1) at 90 cm) in the 1990s to almost no leaching (<0.02 g N m(-2) yr(-1)) since 2006. Forest floor net N mineralization also decreased. This had consequences for spruce needle N concentration (from 17.1 to 11.4 mg kg(-1) in current needles), an increase in litterfall C/N ratio (from 51 to 63), and a significant increase in the Oi + Oe horizon C/N ratio (from 23.4 to 27.3) between 1994 and 2009/2010. Higher forest growth and lower canopy defoliation was observed in the 2000s compared to the 1990s. Our results demonstrate that reducing S deposition has had a profound impact on forest organic matter cycling, leading to a reversal of historic ecosystem N enrichment, cessation of nitrate leaching, and a major loss of accumulated organic soil C and N stocks. These results have major implications for our understanding of the controls on both N saturation and C sequestration in forests, and other ecosystems, subjected to current or historic S deposition.

  • 40.
    Rastak, Narges
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Pajunoja, A.
    Acosta Navarro, Juan Camilo
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ma, J.
    Song, M.
    Partridge, Dan G.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kirkevåg, A.
    Leong, Y.
    Hu, W. W.
    Taylor, N. F.
    Lambe, A.
    Cerully, K.
    Bougiatioti, A.
    Liu, P.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Petaja, T.
    Percival, C.
    Davidovits, P.
    Worsnop, D. R.
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nenes, A.
    Martin, S.
    Jimenez, J. L.
    Collins, D. R.
    Topping, D. O.
    Bertram, A. K.
    Zuend, A.
    Virtanen, A.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Microphysical explanation of the RH-dependent water affinity of biogenic organic aerosol and its importance for climate2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 10, p. 5167-5177Article in journal (Refereed)
    Abstract [en]

    A large fraction of atmospheric organic aerosol (OA) originates from natural emissions that are oxidized in the atmosphere to form secondary organic aerosol (SOA). Isoprene (IP) and monoterpenes (MT) are the most important precursors of SOA originating from forests. The climate impacts from OA are currently estimated through parameterizations of water uptake that drastically simplify the complexity of OA. We combine laboratory experiments, thermodynamic modeling, field observations, and climate modeling to (1) explain the molecular mechanisms behind RH-dependent SOA water-uptake with solubility and phase separation; (2) show that laboratory data on IP- and MT-SOA hygroscopicity are representative of ambient data with corresponding OA source profiles; and (3) demonstrate the sensitivity of the modeled aerosol climate effect to assumed OA water affinity. We conclude that the commonly used single-parameter hygroscopicity framework can introduce significant error when quantifying the climate effects of organic aerosol. The results highlight the need for better constraints on the overall global OA mass loadings and its molecular composition, including currently underexplored anthropogenic and marine OA sources. Plain Language Summary The interaction of airborne particulate matter (aerosols) with water is of critical importance for processes governing climate, precipitation, and public health. It also modulates the delivery and bioavailability of nutrients to terrestrial and oceanic ecosystems. We present a microphysical explanation to the humidity-dependent water uptake behavior of organic aerosol, which challenges the highly simplified theoretical descriptions used in, e.g., present climate models. With the comprehensive analysis of laboratory data using molecular models, we explain the microphysical behavior of the aerosol over the range of humidity observed in the atmosphere, in a way that has never been done before. We also demonstrate the presence of these phenomena in the ambient atmosphere from data collected in the field. We further show, using two state-of-the-art climate models, that misrepresenting the water affinity of atmospheric organic aerosol can lead to significant biases in the estimates of the anthropogenic influence on climate.

  • 41. Rose, C.
    et al.
    Sellegri, K.
    Velarde, F.
    Moreno, I.
    Ramonet, M.
    Weinhold, K.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ginot, Patrick
    Andrade, M.
    Wiedensohler, A.
    Laj, P.
    Frequent nucleation events at the high altitude station of Chacaltaya (5240 m a.s.l.), Bolivia2015In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 102, p. 18-29Article in journal (Refereed)
    Abstract [en]

    While nucleation may represent one of the major processes responsible for the total aerosol number burden in the atmosphere, and especially at high altitude, new particle formation (NPF) events occurring in the upper part of the troposphere are poorly documented in the literature, particularly in the southern hemisphere. NPF events were detected and analyzed at the highest measurement site in the world, Chacaltaya (5240 m a.s.l.), Bolivia between January 1 and December 31 2012, using a Neutral Aerosol and Ion Spectrometer (NAIS) that detects clusters down to 0.4 nm. NPF frequency at Chacaltaya is one of the highest reported so far (63.9%) and shows a clear seasonal dependency with maximum up to 100% during the dry season. This high seasonality of the NPF events frequency was found to be likely linked to the presence of clouds in the vicinity of the station during the wet season. Multiple NPF events are seen on almost 50% of event days and can reach up to 6 events per day, increasing the potential of nucleation to be the major contributor to the particle number concentrations in the upper troposphere. Ion-induced nucleation (IIN) was 14.8% on average, which is higher than the IIN fractions reported for boundary layer stations. The median formation rate of 2 nm particles computed for first position events is increased during the dry season (1.90 cm(-3) s(-1)) compared to the wet season (1.02 cm(-3) s(-1)), showing that events are more intense, on top of being more frequent during the dry season. On the contrary, particle growth rates (GRs) are on average enhanced during the wet season, which could be explained by higher amount of biogenic volatile organic compounds transported from the Amazon rainforest. The NPF events frequency is clearly enhanced when air masses originate from the oceanic sector, with a frequency of occurrence close to 1. However, based on the particle GRs, we calculate that particles most likely nucleate after the oceanic air masses reach the land and are presumably not originating from the marine free troposphere. The high frequency of NPF events, the occurrence of multiple events per day, and the relatively high formation rates observed at Chacaltaya imply that nucleation and growth are likely to be the major mechanism feeding the upper atmosphere with aerosol particles in this part of the continent.

  • 42. Rose, Clemence
    et al.
    Sellegri, Karine
    Moreno, Isabel
    Velarde, Fernando
    Ramonet, Michel
    Weinhold, Kay
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Andrade, Marcos
    Wiedensohler, Alfred
    Ginot, Patrick
    Laj, Paolo
    CCN production by new particle formation in the free troposphere2017In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, no 2, p. 1529-1541Article in journal (Refereed)
    Abstract [en]

    Global models predict that new particle formation (NPF) is, in some environments, responsible for a substantial fraction of the total atmospheric particle number concentration and subsequently contributes significantly to cloud condensation nuclei (CCN) concentrations. NPF events were frequently observed at the highest atmospheric observatory in the world, on Chacaltaya (5240 m a.s.l.), Bolivia. The present study focuses on the impact of NPF on CCN population. Neutral cluster and Air Ion Spectrometer and mobility particle size spectrometer measurements were simultaneously used to follow the growth of particles from cluster sizes down to similar to 2 nm up to CCN threshold sizes set to 50, 80 and 100 nm. Using measurements performed between 1 January and 31 December 2012, we found that 61% of the 94 analysed events showed a clear particle growth and significant enhancement of the CCN-relevant particle number concentration. We evaluated the contribution of NPF, relative to the transport and growth of pre-existing particles, to CCN size. The averaged production of 50 nm particles during those events was 5072, and 1481 cm(-3) for 100 nm particles, with a larger contribution of NPF compared to transport, especially during the wet season. The data set was further segregated into boundary layer (BL) and free troposphere (FT) conditions at the site. The NPF frequency of occurrence was higher in the BL (48 %) compared to the FT (39 %). Particle condensational growth was more frequently observed for events initiated in the FT, but on average faster for those initiated in the BL, when the amount of condensable species was most probably larger. As a result, the potential to form new CCN was higher for events initiated in the BL (67% against 53% in the FT). In contrast, higher CCN number concentration increases were found when the NPF process initially occurred in the FT, under less polluted conditions. This work highlights the competition between particle growth and the removal of freshly nucleated particles by coagulation processes. The results support model predictions which suggest that NPF is an effective source of CCN in some environments, and thus may influence regional climate through cloud-related radiative processes.

  • 43. Schmeissner, T.
    et al.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Birmili, W.
    Wiedensohler, A.
    Hochschild, G.
    Gross, J.
    Hoffmann, P.
    Calderon, S.
    Analysis of number size distributions of tropical free tropospheric = rosol particles observed at Pico Espejo (4765 m a.s.l.), Venezuela2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 7, p. 3319-3332Article in journal (Refereed)
    Abstract [en]

    The first long-term measurements of aerosol number and size distributions in South-American tropical free troposphere (FT) were performed from March 2007 until March 2009. The measurements took place at the high altitude Atmospheric Research Station Alexander von Humboldt. The station is located on top of the Sierra Nevada mountain ridge at 4765 m a.s.l. nearby the city of Merida, Venezuela. Aerosol size distribution and number concentration data was obtained with a custom-built Differential Mobility Particle Sizer (DMPS) system and a Condensational Particle Counter (CPC). The analysis of the annual and diurnal variability of the tropical FT aerosol focused mainly on possible links to the atmospheric general circulation in the tropics. Considerable annual and diurnal cycles of the particle number concentration were observed. Highest total particle number concentrations were measured during the dry season (January-March, 519+/-613 cm(-3)), lowest during the wet season (July September, 318+/-194 cm(-3)). The more humid FT (relative humidity (RH) range 50-95 %) contained generally higher aerosol particle number concentrations (573+/-768 cm(-3) during dry season, 320+/-195 cm(-3) during wet season) than the dry FT (RH <50 %, 454+/-332 cm(-3) during dry season, 275+/-172 cm(-3) during wet season), indicating the importance of convection for aerosol distributions in the tropical FT. The diurnal cycle in the variability of the particle number concentration was mainly driven by local orography.

  • 44. Schobesberger, Siegfried
    et al.
    Vaananen, Riikka
    Leino, Katri
    Virkkula, Aki
    Backman, John
    Pohja, Toivo
    Siivola, Erkki
    Franchin, Alessandro
    Mikkila, Jyri
    Paramonov, Mikhail
    Aalto, Pasi P.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). University of Helsinki .
    Petaja, Tuukka
    Kulmala, Markku
    Airborne measurements over the boreal forest of southern Finland during new particle formation events in 2009 and 20102013In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 18, no 2, p. 145-163Article in journal (Refereed)
    Abstract [en]

    Schobesberger, S., Vaananen, R., Leino, K., Virkkula, A., Backman, J., Pohja, T., Siivola, E., Franchin, A., Mikkila, J., Paramonov, M., Aalto, P.P., Krejci, R., Petaja, T. & Kulmala, M. 2013: Airborne measurements over the boreal forest of southern Finland during new particle formation events in 2009 and 2010. Boreal Env. Res. 18: 145-163. We conducted airborne observations of aerosol physical properties over the southern Finland boreal forest environment. The aim was to investigate the lower tropospheric aerosol (up to 4-km altitude) over an area of 250 by 200 km, in particular during new particle formation (NPF) events, and to address the spatial variability of aerosol number concentration and number size distribution. The regional NPF events, detected both airborne and at the ground, with air masses originating from the Arctic or northern Atlantic Ocean were studied throughout the boundary layer and throughout the area covered. Three suitable case studies are presented in more detail. In two of these studies, the concentrations of nucleation mode particles (3-10 nm in diameter) were found considerably higher (up to a factor of 30) in the upper parts of the planetary boundary layer compared to ground-based measurements during the nucleation events. The observed vertical variation can be connected to boundary layer dynamics and interactions between the boundary layer and the lower free troposphere, likely yielding high concentrations of newly formed aerosol particles. Our results suggest that nucleation does not necessarily occur close to the surface. In one presented case we found evidence of NPF occurring in a limited area above cloud, in the complete absence of a regional NPF event.

  • 45. Spracklen, D. V.
    et al.
    Carslaw, K. S.
    Merikanto, J.
    Mann, G. W.
    Reddington, C. L.
    Pickering, S.
    Ogren, J. A.
    Andrews, E.
    Baltensperger, U.
    Weingartner, E.
    Boy, M.
    Kulmala, M.
    Laakso, L.
    Lihavainen, H.
    Kivekas, N.
    Komppula, M.
    Mihalopoulos, N.
    Kouvarakis, G.
    Jennings, S. G.
    O'Dowd, C.
    Birmili, W.
    Wiedensohler, A.
    Weller, R.
    Gras, J.
    Laj, P.
    Sellegri, K.
    Bonn, B.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Laaksonen, A.
    Hamed, A.
    Minikin, A.
    Harrison, R. M.
    Talbot, R.
    Sun, J.
    Explaining global surface aerosol number concentrations in terms of primary emissions and particle formation2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 10, p. 4775-4793Article in journal (Refereed)
    Abstract [en]

    We synthesised observations of total particle number (CN) concentration from 36 sites around the world. We found that annual mean CN concentrations are typically 300-2000 cm(-3) in the marine boundary layer and free troposphere (FT) and 1000-10 000 cm(-3) in the continental boundary layer (BL). Many sites exhibit pronounced seasonality with summer time concentrations a factor of 2-10 greater than wintertime concentrations. We used these CN observations to evaluate primary and secondary sources of particle number in a global aerosol microphysics model. We found that emissions of primary particles can reasonably reproduce the spatial pattern of observed CN concentration (R-2=0.46) but fail to explain the observed seasonal cycle (R-2=0.1). The modeled CN concentration in the FT was biased low (normalised mean bias, NMB=-88%) unless a secondary source of particles was included, for example from binary homogeneous nucleation of sulfuric acid and water (NMB=-25%). Simulated CN concentrations in the continental BL were also biased low (NMB=-74%) unless the number emission of anthropogenic primary particles was increased or a mechanism that results in particle formation in the BL was included. We ran a number of simulations where we included an empirical BL nucleation mechanism either using the activation-type mechanism (nucleation rate, J, proportional to gas-phase sulfuric acid concentration to the power one) or kinetic-type mechanism (J proportional to sulfuric acid to the power two) with a range of nucleation coefficients. We found that the seasonal CN cycle observed at continental BL sites was better simulated by BL particle formation (R-2=0.3) than by increasing the number emission from primary anthropogenic sources (R-2=0.18). The nucleation constants that resulted in best overall match between model and observed CN concentrations were consistent with values derived in previous studies from detailed case studies at individual sites. In our model, kinetic and activation-type nucleation parameterizations gave similar agreement with observed monthly mean CN concentrations.

  • 46.
    Ström, J
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Engvall, A.-C.
    Delbart, F.
    Krejci, R
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Treffeisen, R.
    On small particles in the Arctic summer boundary layer: observations at two different heights near Ny-Ålesund, Svalbard2008In: Tellus BArticle in journal (Refereed)
  • 47.
    Ström, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Engvall, A.-C.
    Delbart, F.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Treffeisen, R.
    On small particles in the Arctic summer boundary layer: observations at two different heights near Ny-Ålesund, Svalbard2009In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 61, no 2, p. 473-482Article in journal (Refereed)
    Abstract [en]

    Concurrent observations of particle number densities and size distributions observed at two different heights (near ocean level and 475 m above sea level) in Ny-Ålesund, Svalbard were studied with respect to the diurnal variation during a summer period in June 2004. The results show that observed variation in particle number density in the Arctic boundary layer may be strongly modulated by vertical mixing and dilution. The particles appeared to be formed in the early morning when solar intensity reached about 30% of the mid-day intensity. Based on differences in the observed number densities at the two heights it appears as if particles are formed in the lower part of the boundary layer. The formation rate of 10 nm diameter particles is estimated to be 0.11 cm−3 s−1 and the growth rate is in a range between 1 and 2 nm h−1.

  • 48.
    Ström, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Zábori, Julia
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ekman, Annica
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Arctic Ocean water:  A source of light absorbing particles to the atmosphereArticle in journal (Refereed)
  • 49. Targino, Admir C.
    et al.
    Noone, Kevin J
    Drewick, F
    Schneider, J
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Meteorology.
    Olivares, Gustavo
    Department of Applied Environmental Science (ITM).
    Hings, S
    Borrman, S
    Microphysical and chemical characteristics of cloud droplet residuals and interstitial particles in continental stratocumulus clouds2007In: Atmospheric Research, ISSN 0169-8095, Vol. 86, no 3-4, p. 225-240Article in journal (Refereed)
  • 50. Treffeisen, R.
    et al.
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Meteorology.
    Ström, Johan
    Department of Applied Environmental Science (ITM).
    Engvall, Ann-Christine
    Stockholm University, Faculty of Science, Department of Meteorology.
    Herber, A.
    Thomason, L.W.
    Humidity observations in the Arctic troposphere over Ny-Ålesund, Svalbard based on 14 years of radiosonde data.2007In: Atmos. Chem. Phys. Discuss., Vol. 7, p. 1261-1293Article in journal (Refereed)
12 1 - 50 of 60
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