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  • 1.
    Acosta Navarro, Juan C.
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Pausata, Francesco S. R.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Lewinschal, Anna
    Stockholm University, Faculty of Science, Department of Meteorology .
    Varma, Vidya
    Seland, Øyvind
    Gauss, Michael
    Iversen, Trond
    Kirkevåg, Alf
    Riipinen, Ilona
    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.
    Future response of temperature and precipitation to reduced aerosol emissions as compared with increased greenhouse gas concentrations2017In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 30, no 3, p. 939-954Article in journal (Refereed)
    Abstract [en]

    Experiments with a climate model (NorESM1) were performed to isolate the effects of aerosol particles and greenhouse gases on surface temperature and precipitation in simulations of future climate. The simulations show that by 2025-2049, a reduction of aerosol emissions from fossil fuels following a maximum technically feasible reduction (MFR) scenario could lead to a global and Arctic warming of 0.26 K and 0.84 K, respectively; as compared with a simulation with fixed aerosol emissions at the level of 2005. If fossil fuel emissions of aerosols follow a current legislation emissions (CLE) scenario, the NorESM1 model simulations yield a non-significant change in global and Arctic average surface temperature as compared with aerosol emissions fixed at year 2005. The corresponding greenhouse gas effect following the RCP4.5 emission scenario leads to a global and Arctic warming of 0.35 K and 0.94 K, respectively.

    The model yields a marked annual average northward shift in the inter-tropical convergence zone with decreasing aerosol emissions and subsequent warming of the northern hemisphere. The shift is most pronounced in the MFR scenario but also visible in the CLE scenario. The modeled temperature response to a change in greenhouse gas concentrations is relatively symmetric between the hemispheres and there is no marked shift in the annual average position of the inter-tropical convergence zone. The strong reduction in aerosol emissions in MFR also leads to a net southward cross-hemispheric energy transport anomaly both in the atmosphere and ocean, and enhanced monsoon circulation in Southeast and East Asia causing an increase in precipitation over a large part of this region.

  • 2.
    Acosta Navarro, Juan Camilo
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Varma, Vidya
    Stockholm University, Faculty of Science, Department of Meteorology .
    Riipinen, Irina
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Seland, O.
    Kirkevag, A.
    Struthers, Hamish
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Linköping University, Sweden.
    Iversen, T.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Amplification of Arctic warming by past air pollution reductions in Europe2016In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 9, no 4, p. 277-+Article in journal (Refereed)
    Abstract [en]

    The Arctic region is warming considerably faster than the rest of the globe(1), with important consequences for the ecosystems(2) and human exploration of the region(3). However, the reasons behind this Arctic amplification are not entirely clear(4). As a result of measures to enhance air quality, anthropogenic emissions of particulate matter and its precursors have drastically decreased in parts of the Northern Hemisphere over the past three decades(5). Here we present simulations with an Earth system model with comprehensive aerosol physics and chemistry that show that the sulfate aerosol reductions in Europe since 1980 can potentially explain a significant fraction of Arctic warming over that period. Specifically, the Arctic region receives an additional 0.3Wm(-2) of energy, and warms by 0.5 degrees C on annual average in simulations with declining European sulfur emissions in line with historical observations, compared with a model simulation with fixed European emissions at 1980 levels. Arctic warming is amplified mainly in fall and winter, but the warming is initiated in summer by an increase in incoming solar radiation as well as an enhanced poleward oceanic and atmospheric heat transport. The simulated summertime energy surplus reduces sea-ice cover, which leads to a transfer of heat from the Arctic Ocean to the atmosphere. We conclude that air quality regulations in the Northern Hemisphere, the ocean and atmospheric circulation, and Arctic climate are inherently linked.

  • 3. Asmi, A.
    et al.
    Wiedensohler, A.
    Laj, P.
    Fjaeraa, A. -M
    Sellegri, K.
    Birmili, W.
    Weingartner, E.
    Baltensperger, U.
    Zdimal, V.
    Zikova, N.
    Putaud, J. -P
    Marinoni, A.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Fiebig, M.
    Kivekas, N.
    Lihavainen, H.
    Asmi, E.
    Ulevicius, V.
    Aalto, P. P.
    Swietlicki, E.
    Kristensson, A.
    Mihalopoulos, N.
    Kalivitis, N.
    Kalapov, I.
    Kiss, G.
    de Leeuw, G.
    Henzing, B.
    Harrison, R. M.
    Beddows, D.
    O'Dowd, C.
    Jennings, S. G.
    Flentje, H.
    Weinhold, K.
    Meinhardt, F.
    Ries, L.
    Kulmala, M.
    Number size distributions and seasonality of submicron particles in = rope 2008-20092011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 11, p. 5505-5538Article in journal (Refereed)
    Abstract [en]

    Two years of harmonized aerosol number size distribution data from 24 = ropean field monitoring sites have been analysed. The results give a = mprehensive overview of the European near surface aerosol particle = mber concentrations and number size distributions between 30 and 500 = of dry particle diameter. Spatial and temporal distribution of = rosols in the particle sizes most important for climate applications = e presented. We also analyse the annual, weekly and diurnal cycles of = e aerosol number concentrations, provide log-normal fitting parameters = r median number size distributions, and give guidance notes for data = ers. Emphasis is placed on the usability of results within the aerosol = delling community.

  • 4. Beddows, D. C. S.
    et al.
    Dall'Osto, M.
    Harrison, R. M.
    Kulmala, M.
    Asmi, A.
    Wiedensohler, A.
    Laj, P.
    Fjaeraa, A. M.
    Sellegri, K.
    Birmili, W.
    Bukowiecki, N.
    Weingartner, E.
    Baltensperger, U.
    Zdimal, V.
    Zikova, N.
    Putaud, J-P
    Marinoni, A.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Fiebig, M.
    Kivekas, N.
    Swietlicki, E.
    Lihavainen, H.
    Asmi, E.
    Ulevicius, V.
    Aalto, P. P.
    Mihalopoulos, N.
    Kalivitis, N.
    Kalapov, I.
    Kiss, G.
    de Leeuw, G.
    Henzing, B.
    O'Dowd, C.
    Jennings, S. G.
    Flentje, H.
    Meinhardt, F.
    Ries, L.
    van der Gon, H. A. C. Denier
    Visschedijk, A. J. H.
    Variations in tropospheric submicron particle size distributions across the European continent 2008-20092014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 8, p. 4327-4348Article in journal (Refereed)
    Abstract [en]

    Cluster analysis of particle number size distributions from background sites across Europe is presented. This generated a total of nine clusters of particle size distributions which could be further combined into two main groups, namely: a south-to-north category (four clusters) and a west-to-east category (five clusters). The first group was identified as most frequently being detected inside and around northern Germany and neighbouring countries, showing clear evidence of local afternoon nucleation and growth events that could be linked to movement of air masses from south to north arriving ultimately at the Arctic contributing to Arctic haze. The second group of particle size spectra proved to have narrower size distributions and collectively showed a dependence of modal diameter upon the longitude of the site (west to east) at which they were most frequently detected. These clusters indicated regional nucleation (at the coastal sites) growing to larger modes further inland. The apparent growth rate of the modal diameter was around 0.6-0.9 nm h(-1). Four specific air mass back-trajectories were successively taken as case studies to examine in real time the evolution of aerosol size distributions across Europe. While aerosol growth processes can be observed as aerosol traverses Europe, the processes are often obscured by the addition of aerosol by emissions en route. This study revealed that some of the 24 stations exhibit more complex behaviour than others, especially when impacted by local sources or a variety of different air masses. Overall, the aerosol size distribution clustering analysis greatly simplifies the complex data set and allows a description of aerosol aging processes, which reflects the longer-term average development of particle number size distributions as air masses advect across Europe.

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

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

  • 6. Dal Maso, Miikka
    et al.
    Hyvaerinen, Antti
    Komppula, Mika
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Kerminen, Veli-Matti
    Lihavainen, Heikki
    Viisanen, Yrjoe
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Kulmala, Markku
    Annual and interannual variation in boreal forest aerosol particle number and volume concentration and their connection to particle formation2008In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 60, no 4, p. 495-508Article in journal (Refereed)
    Abstract [en]

    We investigated size-resolved submicrometre aerosol particle number and volume concentration time series as well as aerosol dynamic parameters derived front Differential Mobility Particle Sizer (DMPS) measurements at five background stations in the Nordic boreal forest area. The stations in question were Aspvreten, Hyytiala and Uto in Southern Finland and Sweden, and Varrio and Pallas in the Finnish Lapland. The objective Of Our investigation was to identify and quantity annual and interannual variation observable in the time series. We found that the total number and mass concentrations were touch lower at the Lapland stations than at the southern stations and that the total particle number was strongly correlated to particle formation event frequency. The annual total number concentration followed the annual distribution of particle formation events at the Southern stations but much less clearly at the Lapland stations. The volume concentration was highest during summer, in line with higher condensation growth rates: this is in line with the assumption that a large part of the particle volume is produced by oxidized plant emissions. The decrease of sulphate emissions in Europe was not visible in our data set. Aerosol dynamic parameters such as condensation sink, condensation sink diameter and the power law exponent linking coagulation losses and condensation sink are presented to characterize the submicron Nordic background aerosol.

  • 7. 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.

  • 8.
    Ekström, S
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Nozière, B
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, H
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    The CCN Properties of 2-Methyltetrols and C3-C6 Polyols2008In: ICCP 2008: August 28-30, Cluj-Napoca, Romania, 2008Conference paper (Refereed)
  • 9.
    Ekström, Sanna
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Nozière, Barbara
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Hans Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    First direct measurements of the CCN properties of 2-methyltetrols and polyols2008In: Geophysical Research Abstracts, 2008Conference paper (Refereed)
    Abstract [en]

    2-methyltetrols and polyols have received a lot of attention in recent years. 2-methyltetrols have been found in aerosols in various regions are believed to be formed by the oxidation of isoprene. Polyols are produced by fungi and have been measured

    in large concentrations in aerosols. The main reason of interest of both 2-methyltetrols and polyols as efficient cloud condensation nuclei (CCN) is due to their high solubility.

    This presentation will report for the first time the experimental determination of complete Köhler curves for 2-methyltetrols (2-methylerythritol and 2-methylthreitol), C3 to C6 polyols (glycerol, erythritol, arabitol, and mannitol), and for comparison their

    analogue di-acids (malonic acid, succinic acid and, adipic acid). The original Köhler equations were determined from osmolality and tensiometry measurements of the compounds both in water and salt solutions (sodium chloride and ammonium sulphate).

    The results indicate that the polyols generally have similar CCN properties as the dicarboxylic acids. The critical supersaturation for aerosol particles with a 30 nm radius were: 2-methyltetrol; 0.68%, mannitol; 0.62%, arabitol; 0.60%, 2-methylerythritol;

    0.57%, erythritol; 0.56%, glycerol; 0.53%, adipic acid; 0.52%, succinic acid; 0.49%, and malonic acid; 0.44%. Mixtures of salts had lower critical supersaturation than water solutions, especially for the polyols. One exception was 2-methylerythritol, which interestingly was less efficient as CCN in salt solutions.

    The CCN efficiency of the polyols is believed to result mostly from their large water affinity, enforcing the Raoult effect, while organic acids lower the Kelvin effect. The very large solubility of polyols compared to the di-acids mean that they could positive effect in the initial phase of the droplet growth while the di-acids cannot. 2-methyltetrols were found to have both a Kelvin and a Raoult effect.

    In addition, these results establish for the first time that the 3-dimensional structure of molecules can have an effect on their CCN properties. The two isomers of the 2-methyltetrols have significantly different CCN properties that are also influenced

    oppositely in the presence of salts.

  • 10.
    Ekström, Sanna
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Nozière, Barbara
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    The Cloud Condensation Nuclei (CCN) properties of 2-methyltetrols and C3-C6 polyols from osmolality and surface tension measurements2009In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 9, no 3, p. 973-980Article in journal (Refereed)
    Abstract [en]

    A significant fraction of the organic material in aerosols is made of highly soluble compounds such as sugars (mono-and polysaccharides) and polyols such as the 2-methyltetrols, methylerythritol and methyltreitol. Because of their high solubility these compounds are considered as potentially efficient CCN material. For the 2-methyltetrols, this would have important implications for cloud formation at global scale because they are thought to be produced by the atmospheric oxidation of isoprene. To investigate this question, the complete Kohler curves for C3-C6 polyols and the 2-methyltetrols have been determined experimentally from osmolality and surface tension measurements. Contrary to what was expected, none of these compounds displayed a higher CCN efficiency than organic acids. Their Raoult terms show that this limited CCN efficiency is due to their absence of dissociation in water, this in spite of slight surface-tension effects for the 2-methyltetrols. Thus, compounds such as saccharides and polyols would not contribute more to cloud formation than other organic compounds studied so far. In particular, the presence of 2-methyltetrols in aerosols would not particularly enhance cloud formation in the atmosphere, in contrary to recently suggested

  • 11.
    Ekström, Sanna
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nozière, Barbara
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    The Cloud Condensation Nuclei (CCN) properties of 2-methyltetrols and C3–C6 polyols from osmolality and surface tension measurements (Discussion paper)2008In: Atmospheric Chemistry and Physics Discussion, ISSN 1680-7367, Vol. 8, no 5, p. 17237-17256Article in journal (Refereed)
    Abstract [en]

    A significant fraction of the organic material in aerosols is made of highly soluble compounds such as sugars (mono- and polysaccharides) and polyols, including the 2-methyltetrols, methylerythritol and methyltreitol. The high solubility of these compounds has brought the question of their potentially high CCN efficiency. For the 2-methyltetrols, this would have important implications for cloud formation at global scale because they are thought to be produced by the atmospheric oxidation of isoprene. To investigate this question, the complete Köhler curves for C3–C6 polyols and the 2-methyltetrols have been determined experimentally from osmolality and surface tension measurements. Contrary to what expected, none of these compounds displayed a critical supersaturation lower than those of inorganic salts or organic acids. Their Raoult terms show that this limited CCN efficiency is due to their absence of dissociation in water, this in spite of slight surface-tension effects for the 2-methyltetrols. Thus, compounds such as sugars and polyols would not contribute more to cloud formation in the atmosphere than any other organic compounds studied so far. In particular, the presence of 2-methyltetrols in aerosols would not particularly enhance cloud formation in the atmosphere, contrary to what has been suggested.

  • 12. Genberg, J.
    et al.
    van der Gon, H. A. C. Denier
    Simpson, D.
    Swietlicki, E.
    Areskoug, Hans
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Beddows, D.
    Ceburnis, D.
    Fiebig, M.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Harrison, R. M.
    Jennings, S. G.
    Saarikoski, S.
    Spindler, G.
    Visschedijk, A. J. H.
    Wiedensohler, A.
    Yttri, K. E.
    Bergström, R.
    Light-absorbing carbon in Europe - measurement and modelling, with a focus on residential wood combustion emissions2013In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, no 17, p. 8719-8738Article in journal (Refereed)
    Abstract [en]

    The atmospheric concentration of elemental carbon (EC) in Europe during the six-year period 2005-2010 has been simulated with the EMEP MSC-W model. The model bias compared to EC measurements was less than 20% for most of the examined sites. The model results suggest that fossil fuel combustion is the dominant source of EC in most of Europe but that there are important contributions also from residential wood burning during the cold seasons and, during certain episodes, also from open biomass burning (wildfires and agricultural fires). The modelled contributions from open biomass fires to ground level concentrations of EC were small at the sites included in the present study, <3% of the long-term average of EC in PM10. The modelling of this EC source is subject to many uncertainties, and it was likely underestimated for some episodes. EC measurements and modelled EC were also compared to optical measurements of black carbon (BC). The relationships between EC and BC (as given by mass absorption cross section, MAC, values) differed widely between the sites, and the correlation between observed EC and BC is sometimes poor, making it difficult to compare results using the two techniques and limiting the comparability of BC measurements to model EC results. A new bottom-up emission inventory for carbonaceous aerosol from residential wood combustion has been applied. For some countries the new inventory has substantially different EC emissions compared to earlier estimates. For northern Europe the most significant changes are much lower emissions in Norway and higher emissions in neighbouring Sweden and Finland. For Norway and Sweden, comparisons to source-apportionment data from winter campaigns indicate that the new inventory may improve model-calculated EC from wood burning. Finally, three different model setups were tested with variable atmospheric lifetimes of EC in order to evaluate the model sensitivity to the assumptions regarding hygroscopicity and atmospheric ageing of EC. The standard ageing scheme leads to a rapid transformation of the emitted hydrophobic EC to hygroscopic particles, and generates similar results when assuming that all EC is aged at the point of emission. Assuming hydrophobic emissions and no ageing leads to higher EC concentrations. For the more remote sites, the observed EC concentration was in between the modelled EC using standard ageing and the scenario treating EC as hydrophobic. This could indicate too-rapid EC ageing in the model in relatively clean parts of the atmosphere.

  • 13.
    Hansson, Hans-Christen
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Bhend, Jonas
    Causes of Regional Change - Aerosols2015In: Second Assessment of Climate Change for the Baltic Sea Basin / [ed] The BACC II Author Team, Springer, 2015, p. 441-452Chapter in book (Refereed)
    Abstract [en]

    This chapter starts by introducing the complex nature of atmospheric aerosols, their sources, formation and properties and describes how they interact with clouds. This is important background information for discussing how aerosols affect climate, both directly and indirectly by affecting the radiative properties of clouds. The complexity of the aerosol-cloud-climate interaction causes large uncertainty in the projections of future climate. Results from different modelling studies on the European region are presented, and these show that the large spatial and temporal variations in atmospheric aerosol concentrations and properties have large regional differences in their effect on climate. This chapter concludes with an example of a co-beneficial global air quality and climate change mitigation scenario.

  • 14. Hussein, T.
    et al.
    Johansson, C
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Karlsson, H
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, H
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Factors affecting non-tailpipe aerosol particle emissions from paved roads: on road measurements in Stockholm, Sweden.2008In: Atmos. Environ., Vol. 42, p. 688-702Article in journal (Refereed)
  • 15. Hussein, T.
    et al.
    Johansson, Christer
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Karlsson, Hans
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Factors affecting non-tailpipe aerosol particle emissions from paved roads: on road measurements in Stockholm, Sweden.2007In: Atmos. Environ.Article in journal (Refereed)
  • 16. Hussein, T.
    et al.
    Junninen, H.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Kristensson, A.
    Dal Maso, M.
    Riipinen, I.
    Aalto, P.P.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Swietlicki, E.
    Kulmala, M.
    Time span and spatial scale of regional new particle formation events over Finland and Southern Sweden2009In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 9, no 14, p. 4699-4716Article in journal (Refereed)
    Abstract [en]

    We investigated the time span and spatial scale of regional new particle formation (NPF) events in Finland and Southern Sweden using measured particle number size distributions at five background stations. We define the time span of a NPF event as the time period from the first moment when the newly formed mode of aerosol particles is observable below 25 nm until the newly formed mode is not any more distinguishable from other background modes of aerosol particles after growing to bigger sizes. We identify the spatial scale of regional NPF events based on two independent approaches. The first approach is based on the observation within a network of stationary measurement stations and the second approach is based on the time span and the history of air masses back-trajectories. According to the second approach, about 60% and 28% of the events can be traced to distances longer than 220 km upwind from where the events were observed in Southern Finland (Hyytiälä) and Northern Finland (Värriö), respectively. The analysis also showed that the observed regional NPF events started over the continents but not over the Atlantic Ocean. The first approach showed that although large spatial scale NPF events are frequently observed at several locations simultaneously, they are rarely identical (similar characteristics and temporal variations) due to differences in the initial meteorological and geographical conditions between the stations. The growth of the newly formed particles during large spatial scale events can be followed for more than 30 h where the newly formed aerosol particles end up in the Aitken mode (diameter 25–100 nm) and accumulation mode size ranges (diameter 0.1–1 μm). This study showed clear evidence that regional NPF events can pose a significant source for accumulation mode particles over the Scandinavian continent provided that these findings can be generalized to many of the air masses traveling over the European continent.

  • 17.
    Johansson, Christer
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    PM10 och sot i Sverige.2007Report (Other (popular science, discussion, etc.))
  • 18. 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.

  • 19. 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)
  • 20. Kulmala, M.
    et al.
    Lappalainen, H. K.
    Petaja, T.
    Kurten, T.
    Kerminen, V. -M.
    Viisanen, Y.
    Hari, P.
    Sorvari, S.
    Back, J.
    Bondur, V.
    Kasimov, N.
    Kotlyakov, V.
    Matvienko, G.
    Baklanov, A.
    Guo, H. D.
    Ding, A.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Zilitinkevich, S.
    Introduction: The Pan-Eurasian Experiment (PEEX) - multidisciplinary, multiscale and multicomponent research and capacity-building initiative2015In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 15, no 22, p. 13085-13096Article in journal (Refereed)
    Abstract [en]

    The Pan-Eurasian Experiment (PEEX) is a multidisciplinary, multiscale and multicomponent research, research infrastructure and capacity-building program. PEEX has originated from a bottom-up approach by the science communities and is aiming at resolving the major uncertainties in Earth system science and global sustainability issues concerning the Arctic and boreal pan-Eurasian regions, as well as China. The vision of PEEX is to solve interlinked, global grand challenges influencing human well-being and societies in northern Eurasia and China. Such challenges include climate change; air quality; biodiversity loss; urbanization; chemicalization; food and freshwater availability; energy production; and use of natural resources by mining, industry, energy production and transport sectors. Our approach is integrative and supra-disciplinary, recognizing the important role of the Arctic and boreal ecosystems in the Earth system. The PEEX vision includes establishing and maintaining long-term, coherent and coordinated research activities as well as continuous, comprehensive research and educational infrastructure and related capacity-building across the PEEX domain. In this paper we present the PEEX structure and summarize its motivation, objectives and future outlook.

  • 21. Lappalainen, Hanna K.
    et al.
    Kerminen, Veli-Matti
    Petaja, Tuukka
    Kurten, Theo
    Baklanov, Aleksander
    Shvidenko, Anatoly
    Back, Jaana
    Vihma, Timo
    Alekseychik, Pavel
    Andreae, Meinrat O.
    Arnold, Stephen R.
    Arshinov, Mikhail
    Asmi, Eija
    Belan, Boris
    Bobylev, Leonid
    Chalov, Sergey
    Cheng, Yafang
    Chubarova, Natalia
    de Leeuw, Gerrit
    Ding, Aijun
    Dobrolyubov, Sergey
    Dubtsov, Sergei
    Dyukarev, Egor
    Elansky, Nikolai
    Eleftheriadis, Kostas
    Esau, Igor
    Filatov, Nikolay
    Flint, Mikhail
    Fu, Congbin
    Glezer, Olga
    Gliko, Aleksander
    Heimann, Martin
    Holtslag, Albert A. M.
    Horrak, Urmas
    Janhunen, Juha
    Juhola, Sirkku
    Jarvi, Leena
    Jarvinen, Heikki
    Kanukhina, Anna
    Konstantinov, Pavel
    Kotlyakov, Vladimir
    Kieloaho, Antti-Jussi
    Komarov, Alexander S.
    Kujansuu, Joni
    Kukkonen, Ilmo
    Duplissy, Ella-Maria
    Laaksonen, Ari
    Laurila, Tuomas
    Lihavainen, Heikki
    Lisitzin, Alexander
    Mahura, Alexsander
    Makshtas, Alexander
    Mareev, Evgeny
    Mazon, Stephany
    Matishov, Dmitry
    Melnikov, Vladimir
    Mikhailov, Eugene
    Moisseev, Dmitri
    Nigmatulin, Robert
    Noe, Steffen M.
    Ojala, Anne
    Pihlatie, Mari
    Popovicheva, Olga
    Pumpanen, Jukka
    Regerand, Tatjana
    Repina, Irina
    Shcherbinin, Aleksei
    Shevchenko, Vladimir
    Sipila, Mikko
    Skorokhod, Andrey
    Spracklen, Dominick V.
    Su, Hang
    Subetto, Dmitry A.
    Sun, Junying
    Terzhevik, Arkady Y.
    Timofeyev, Yuri
    Troitskaya, Yuliya
    Tynkkynen, Veli-Pekka
    Kharuk, Viacheslav I.
    Zaytseva, Nina
    Zhang, Jiahua
    Viisanen, Yrjo
    Vesala, Timo
    Hari, Pertti
    Hansson, Hans Christen
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Matvienko, Gennady G.
    Kasimov, Nikolai S.
    Guo, Huadong
    Bondur, Valery
    Zilitinkevich, Sergej
    Kulmala, Markku
    Pan-Eurasian Experiment (PEEX): towards a holistic understanding of the feedbacks and interactions in the land-atmosphere-ocean-society continuum in the northern Eurasian region2016In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 16, no 22, p. 14421-14461Article in journal (Refereed)
    Abstract [en]

    The northern Eurasian regions and Arctic Ocean will very likely undergo substantial changes during the next decades. The Arctic-boreal natural environments play a crucial role in the global climate via albedo change, carbon sources and sinks as well as atmospheric aerosol production from biogenic volatile organic compounds. Furthermore, it is expected that global trade activities, demographic movement, and use of natural resources will be increasing in the Arctic regions. There is a need for a novel research approach, which not only identifies and tackles the relevant multi-disciplinary research questions, but also is able to make a holistic system analysis of the expected feedbacks. In this paper, we introduce the research agenda of the Pan-Eurasian Experiment (PEEX), a multi-scale, multi-disciplinary and international program started in 2012 (https://www.atm.helsinki.fi/peex/). PEEX sets a research approach by which large-scale research topics are investigated from a system perspective and which aims to fill the key gaps in our understanding of the feedbacks and interactions between the land-atmosphereaquatic-society continuum in the northern Eurasian region. We introduce here the state of the art for the key topics in the PEEX research agenda and present the future prospects of the research, which we see relevant in this context.

  • 22.
    Lewinschal, Anna
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Sand, Maria
    Berntsen, Terje K.
    Langner, Joakim
    Local and remote temperature response of regional SO2 emissions2019In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 19, no 4, p. 2385-2403Article in journal (Refereed)
    Abstract [en]

    Short-lived anthropogenic climate forcers (SLCFs), such as sulfate aerosols, affect both climate and air quality. Despite being short-lived, these forcers do not affect temperatures only locally; regions far away from the emission sources are also affected. Climate metrics are often used in a policy context to compare the climate impact of different anthropogenic forcing agents. These metrics typically relate a forcing change in a certain region with a temperature change in another region and thus often require a separate model to convert emission changes to radiative forcing (RF) changes. In this study, we used a coupled Earth system model, NorESM (Norwegian Earth System Model), to calculate emission-to-temperature-response metrics for sulfur dioxide (SO2) emission changes in four different policy-relevant regions: Europe (EU), North America (NA), East Asia (EA) and South Asia (SA). We first increased the SO2 emissions in each individual region by an amount giving approximately the same global average radiative forcing change (-0.45 Wm(-2)). The global mean temperature change per unit sulfur emission compared to the control experiment was independent of emission region and equal to similar to 0.006 K(TgSyr(-1))(-1). On a regional scale, the Arctic showed the largest temperature response in all experiments. The second largest temperature change occurred in the region of the imposed emission increase, except when South Asian emissions were changed; in this experiment, the temperature response was approximately the same in South Asia and East Asia. We also examined the non-linearity of the temperature response by removing all anthropogenic SO2 emissions over Europe in one experiment. In this case, the temperature response (both global and regional) was twice that in the corresponding experiment with a European emission increase. This non-linearity in the temperature response is one of many uncertainties associated with the use of simplified climate metrics.

  • 23. 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.

  • 24. Mann, G. W.
    et al.
    Carslaw, K. S.
    Reddington, C. L.
    Pringle, K. J.
    Schulz, M.
    Asmi, A.
    Spracklen, D. V.
    Ridley, D. A.
    Woodhouse, M. T.
    Lee, L. A.
    Zhang, K.
    Ghan, S. J.
    Easter, R. C.
    Liu, X.
    Stier, P.
    Lee, Y. H.
    Adams, P. J.
    Tost, H.
    Lelieveld, J.
    Bauer, S. E.
    Tsigaridis, K.
    van Noije, T. P. C.
    Strunk, A.
    Vignati, E.
    Bellouin, N.
    Dalvi, M.
    Johnson, C. E.
    Bergman, T.
    Kokkola, H.
    von Salzen, K.
    Yu, F.
    Luo, G.
    Petzold, A.
    Heintzenberg, J.
    Clarke, A.
    Ogren, A.
    Gras, J.
    Baltensperger, U.
    Kaminski, U.
    Jennings, S. G.
    O'Dowd, C. D.
    Harrison, R. M.
    Beddows, D. C. S.
    Kulmala, M.
    Viisanen, Y.
    Ulevicius, V.
    Mihalopoulos, N.
    Zdimal, V.
    Fiebig, M.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Swietlicki, E.
    Henzing, J. S.
    Intercomparison and evaluation of global aerosol microphysical properties among AeroCom models of a range of complexity2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 9, p. 4679-4713Article in journal (Refereed)
    Abstract [en]

    Many of the next generation of global climate models will include aerosol schemes which explicitly simulate the microphysical processes that determine the particle size distribution. These models enable aerosol optical properties and cloud condensation nuclei (CCN) concentrations to be determined by fundamental aerosol processes, which should lead to a more physically based simulation of aerosol direct and indirect radiative forcings. This study examines the global variation in particle size distribution simulated by 12 global aerosol microphysics models to quantify model diversity and to identify any common biases against observations. Evaluation against size distribution measurements from a new European network of aerosol supersites shows that the mean model agrees quite well with the observations at many sites on the annual mean, but there are some seasonal biases common to many sites. In particular, at many of these European sites, the accumulation mode number concentration is biased low during winter and Aitken mode concentrations tend to be overestimated in winter and underestimated in summer. At high northern latitudes, the models strongly underpredict Aitken and accumulation particle concentrations compared to the measurements, consistent with previous studies that have highlighted the poor performance of global aerosol models in the Arctic. In the marine boundary layer, the models capture the observed meridional variation in the size distribution, which is dominated by the Aitken mode at high latitudes, with an increasing concentration of accumulation particles with decreasing latitude. Considering vertical profiles, the models reproduce the observed peak in total particle concentrations in the upper troposphere due to new particle formation, although modelled peak concentrations tend to be biased high over Europe. Overall, the multimodel-mean data set simulates the global variation of the particle size distribution with a good degree of skill, suggesting that most of the individual global aerosol microphysics models are performing well, although the large model diversity indicates that some models are in poor agreement with the observations. Further work is required to better constrain size-resolved primary and secondary particle number sources, and an improved understanding of nucleation and growth (e. g. the role of nitrate and secondary organics) will improve the fidelity of simulated particle size distributions.

  • 25. Monks, P. S.
    et al.
    Granier, C.
    Fuzzi, S.
    Stohl, A.
    Williams, M. L.
    Akimoto, H.
    Amann, M.
    Baklanov, A.
    Baltensperger, U.
    Bey, I.
    Blake, N.
    Blake, R. S.
    Carslaw, K.
    Cooper, O. R.
    Dentener, F.
    Fowler, D.
    Fragkou, E.
    Frost, G. J.
    Generoso, S.
    Ginoux, P.
    Grewe, V.
    Guenther, A.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Henne, S.
    Hjorth, J.
    Hofzumahaus, A.
    Huntrieser, H.
    Isaksen, I. S. A.
    Jenkin, M. E.
    Kaiser, J.
    Kanakidou, M.
    Klimont, Z.
    Kulmala, M.
    Laj, P.
    Lawrence, M. G.
    Lee, J. D.
    Liousse, C.
    Maione, M.
    McFiggans, G.
    Metzger, A.
    Mieville, A.
    Moussiopoulos, N.
    Orlando, J. J.
    O'Dowd, C. D.
    Palmer, P. I.
    Parrish, D. D.
    Petzold, A.
    Platt, U.
    Poeschl, U.
    Prevot, A. S. H.
    Reeves, C. E.
    Reimann, S.
    Rudich, Y.
    Sellegri, K.
    Steinbrecher, R.
    Simpson, D.
    ten Brink, H.
    Theloke, J.
    van der Werf, G. R.
    Vautard, R.
    Vestreng, V.
    Vlachokostas, Ch.
    von Glasow, R.
    Atmospheric composition change: global and regional air quality2009In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 43, no 33, p. 5268-5350Article, review/survey (Refereed)
    Abstract [en]

    Air quality transcends all scales with in the atmosphere from the local to the global with handovers and feedbacks at each scale interaction. Air quality has manifold effects on health, ecosystems heritage and, climate. In this review the state of scientific understanding in relation to global and regional air quality is outlined. The review discusses air quality, in terms of emissions, processing and transport of trace gases and aerosols. New insights into the characterization of both natural and anthropogenic emissions are reviewed looking at both natural (e.g. dust and lightning) as well as plant emissions. Trends in anthropogenic emissions both by region and globally are discussed as well as biomass burning emissions. In terms of chemical processing the major air quality elements of ozone, non-methane hydrocarbons, nitrogen oxides and aerosols are covered. A number of topics are presented as a way of integrating the process view into the atmospheric context; these include the atmospheric oxidation efficiency, halogen and HOx chemistry, nighttime chemistry, tropical chemistry, heat waves, megacities, biomass burning and the regional hot spot of the Mediterranean. New findings with respect to the transport of pollutants across the scales are discussed, in particular the move to quantify the impact of long-range transport on regional air quality. Gaps and research questions that remain intractable are identified. The review concludes with a focus of research and policy questions for the coming decade. In particular, the policy challenges for concerted air quality and climate change policy (co-benefit) are discussed.

  • 26.
    Olivares, Gustavo
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Johansson, Christer
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    The role of ambient temperature for particle number concentrations in a street canyon.2007In: Atmos. Environ., Vol. 41, p. 2145-2155Article in journal (Refereed)
  • 27. Putaud, J. -P
    et al.
    Van Dingenen, R.
    Alastuey, A.
    Bauer, H.
    Birmili, W.
    Cyrys, J.
    Flentje, H.
    Fuzzi, S.
    Gehrig, R.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Harrison, R. M.
    Herrmann, H.
    Hitzenberger, R.
    Hueglin, C.
    Jones, A. M.
    Kasper-Giebl, A.
    Kiss, G.
    Kousa, A.
    Kuhlbusch, T. A. J.
    Loeschau, G.
    Maenhaut, W.
    Molnar, A.
    Moreno, T.
    Pekkanen, J.
    Perrino, C.
    Pitz, M.
    Puxbaum, H.
    Querol, X.
    Rodriguez, S.
    Salma, I.
    Schwarz, J.
    Smolik, J.
    Schneider, J.
    Spindler, G.
    ten Brink, H.
    Tursic, J.
    Viana, M.
    Wiedensohler, A.
    Raes, F.
    A European aerosol phenomenology-3: Physical and chemical characteristics of particulate matter from 60 rural, urban, and kerbside sites across Europe2010In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 44, no 10, p. 1308-1320Article in journal (Refereed)
    Abstract [en]

    This paper synthesizes data on aerosol (particulate matter, PM) physical and chemical characteristics, which were obtained over the past decade in aerosol research and monitoring activities at more than 60 natural background, rural, near-city, urban, and kerbside sites across Europe. The data include simultaneously measured PM10 and/or PM2.5 mass on the one hand, and aerosol particle number concentrations or PM chemistry on the other hand. The aerosol data presented in our previous works (Van Dingenen et al., 2004; Putaud et al., 2004) were updated and merged to those collected in the framework of the EU supported European Cooperation in the field of Scientific and Technical action COST633 (Particulate matter: Properties related to health effects). A number of conclusions from our previous studies were confirmed. There is no single ratio between PM2.5 and PM10 mass concentrations valid for all sites, although fairly constant ratios ranging from 0.5 to 0.9 are observed at most individual sites. There is no general correlation between PM mass and particle number concentrations, although particle number concentrations increase with PM2.5 levels at most sites. The main constituents of both PM10 and PM2.5 are generally organic matter, sulfate and nitrate. Mineral dust can also be a major constituent of PM10 at kerbside sites and in Southern Europe. There is a clear decreasing gradient in SO42- and NO3- contribution to PM10 when moving from rural to urban to kerbside sites. In contrast, the total carbon/PM10 ratio increases from rural to kerbside sites. Some new conclusions were also drawn from this work: the ratio between ultrafine particle and total particle number concentration decreases with PM2.5 concentration at all sites but one, and significant gradients in PM chemistry are observed when moving from Northwestern, to Southern to Central Europe. Compiling an even larger number of data sets would have further increased the significance of our conclusions, but collecting all the aerosol data sets obtained also through research projects remains a tedious task.

  • 28. Reddington, C. L.
    et al.
    Carslaw, K. S.
    Spracklen, D. V.
    Frontoso, M. G.
    Collins, L.
    Merikanto, J.
    Minikin, A.
    Hamburger, T.
    Coe, H.
    Kulmala, M.
    Aalto, P.
    Flentje, H.
    Plass-Duelmer, C.
    Birmili, W.
    Wiedensohler, A.
    Wehner, B.
    Tuch, T.
    Sonntag, A.
    O'Dowd, C. D.
    Jennings, S. G.
    Dupuy, R.
    Baltensperger, U.
    Weingartner, E.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Laj, P.
    Sellegri, K.
    Boulon, J.
    Putaud, J. -P
    Gruening, C.
    Swietlicki, E.
    Roldin, P.
    Henzing, J. S.
    Moerman, M.
    Mihalopoulos, N.
    Kouvarakis, G.
    Zdimal, V.
    Zikova, N.
    Marinoni, A.
    Bonasoni, P.
    Duchi, R.
    Primary versus secondary contributions to particle number concentrations in the European boundary layer2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 23, p. 12007-12036Article in journal (Refereed)
    Abstract [en]

    It is important to understand the relative contribution of primary and secondary particles to regional and global aerosol so that models can attribute aerosol radiative forcing to different sources. In large-scale models, there is considerable uncertainty associated with treatments of particle formation (nucleation) in the boundary layer (BL) and in the size distribution of emitted primary particles, leading to uncertainties in predicted cloud condensation nuclei (CCN) concentrations. Here we quantify how primary particle emissions and secondary particle formation influence size-resolved particle number concentrations in the BL using a global aerosol microphysics model and aircraft and ground site observations made during the May 2008 campaign of the European Integrated Project on Aerosol Cloud Climate Air Quality Interactions (EUCAARI). We tested four different parameterisations for BL nucleation and two assumptions for the emission size distribution of anthropogenic and wildfire carbonaceous particles. When we emit carbonaceous particles at small sizes (as recommended by the Aerosol Inter-comparison project, AEROCOM), the spatial distributions of campaign-mean number concentrations of particles with diameter >50 nm (N(50)) and >100 nm (N(100)) were well captured by the model (R(2)>= 0.8) and the normalised mean bias (NMB) was also small (-18% for N(50) and -1% for N(100)). Emission of carbonaceous particles at larger sizes, which we consider to be more realistic for low spatial resolution global models, results in equally good correlation but larger bias (R(2)>= 0.8, NMB = -52% and -29%), which could be partly but not entirely compensated by BL nucleation. Within the uncertainty of the observations and accounting for the uncertainty in the size of emitted primary particles, BL nucleation makes a statistically significant contribution to CCN-sized particles at less than a quarter of the ground sites. Our results show that a major source of uncertainty in CCN-sized particles in polluted European air is the emitted size of primary carbonaceous particles. New information is required not just from direct observations, but also to determine the effective emission size and composition of primary particles appropriate for different resolution models.

  • 29. Simpson, David
    et al.
    Bartnicki, Jerzy
    Jalkanen, Jukka-Pekka
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hertel, Ole
    Langner, Joakim
    Pryor, Sara C.
    Environmental Impacts - Atmospheric Chemistry2015In: Second Assessment of Climate Change for the Baltic Sea Basin / [ed] The BACC II Author Team, Springer, 2015, p. 267-289Chapter in book (Refereed)
    Abstract [en]

    This chapter addresses sources and trends of atmospheric pollutants and deposition in relation to the Baltic Sea region. Air pollution is shown to have important effects, including significant contributions to nitrogen loading of the Baltic Sea area, ecosystem impacts due to acidifying and eutrophying pollutants and ozone, and human health impacts. Compounds such as sulphate and ozone also have climate impacts. Emission changes have been very significant over the past 100 years, although very different for land-and sea-based sources. Land-based emissions generally peaked around 1980-1990 and have since reduced due to emissions control measures. Emissions from shipping have been steadily increasing for decades, but recent measures have reduced sulphur and particulate emissions. Future developments depend strongly on policy developments. Changes in concentration and deposition of the acidifying components generally follow emission changes within the European area. Mean ozone levels roughly doubled during the twentieth century across the northern hemisphere, but peak levels have reduced in many regions in the past 20 years. The main changes in air pollution in the Baltic Sea region are due to changes in emissions rather than to climate change.

  • 30. Suni, T.
    et al.
    Guenther, A.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Kulmala, M.
    Andreae, M. O.
    Arneth, A.
    Artaxo, P.
    Blyth, E.
    Brus, M.
    Ganzeveldi, L.
    Kabat, P.
    de Noblet-Ducoudre, N.
    Reichstein, M.
    Reissell, A.
    Rosenfeld, D.
    Seneviratne, S.
    The significance of land-atmosphere interactions in the Earth system-iLEAPS achievements and perspectives2015In: Anthropocene, E-ISSN 2213-3054, Vol. 12, p. 69-84Article in journal (Refereed)
    Abstract [en]

    The integrated land ecosystem-atmosphere processes study (iLEAPS) is an international research project focussing on the fundamental processes that link land-atmosphere exchange, climate, the water cycle, and tropospheric chemistry. The project, iLEAPS, was established 2004 within the International Geosphere-Biosphere Programme (IGBP). During its first decade, iLEAPS has proven to be a vital project, well equipped to build a community to address the challenges involved in understanding the complex Earth system: multidisciplinary, integrative approaches for both observations and modeling. The iLEAPS community has made major advances in process understanding, land-surface modeling, and observation techniques and networks. The modes of iLEAPS operation include elucidating specific iLEAPS scientific questions through networks of process studies, field campaigns, modeling, long-term integrated field studies, international interdisciplinary mega-campaigns, synthesis studies, databases, as well as conferences on specific scientific questions and synthesis meetings. Another essential component of iLEAPS is knowledge transfer and it also encourages community-and policy-related outreach activities associated with the regional integrative projects. As a result of its first decade of work, iLEAPS is now setting the agenda for its next phase (2014-2024) under the new international initiative, future Earth. Human influence has always been an important part of land-atmosphere science but in order to respond to the new challenges of global sustainability, closer ties with social science and economics groups will be necessary to produce realistic estimates of land use and anthropogenic emissions by analysing future population increase, migration patterns, food production allocation, land management practices, energy production, industrial development, and urbanization.

  • 31. Swietlicki, E.
    et al.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hameri, K.
    Svenningsson, B.
    Massling, A.
    McFiggans, G.
    McMurry, P. H.
    Petaja, T.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gysel, M.
    Topping, D.
    Weingartner, E.
    Baltensperger, U.
    Rissler, J.
    Wiedensohler, A.
    Kulmala, M.
    Hygroscopic properties of submicrometer atmospheric aerosol particles measured with H-TDMA instruments in various environments : a review2008In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 60, no 3, p. 432-469Article, review/survey (Refereed)
    Abstract [en]

    The hygroscopic properties play a vital role for the direct and indirect effects of aerosols on climate, as well as the health effects of particulate matter (PM) by modifying the deposition pattern of inhaled particles in the humid human respiratory tract. Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) instruments have been used in field campaigns in various environments globally over the last 25 yr to determine the water uptake on submicrometre particles at subsaturated conditions. These investigations have yielded valuable and comprehensive information regarding the particle hygroscopic properties of the atmospheric aerosol, including state of mixing. These properties determine the equilibrium particle size at ambient relative humidities and have successfully been used to calculate the activation of particles at water vapour supersaturation. This paper summarizes the existing published H-TDMA results on the size-resolved submicrometre aerosol particle hygroscopic properties obtained from ground-based measurements at multiple marine, rural, urban and free tropospheric measurement sites. The data is classified into groups of hygroscopic growth indicating the external mixture, and providing clues to the sources and processes controlling the aerosol. An evaluation is given on how different chemical and physical properties affect the hygroscopic growth.

  • 32.
    Tesche, Matthias
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Rastak, Narges
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Charlson, R. J.
    Glantz, Paul
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Reconciling aerosol light extinction measurements from spaceborne lidar observations and in situ measurements in the Arctic2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 15, p. 7869-7882Article in journal (Refereed)
    Abstract [en]

    In this study we investigate to what degree it is possible to reconcile continuously recorded particle light extinction coefficients derived from dry in situ measurements at Zeppelin station (78.92 degrees N, 11.85 degrees E; 475 m above sea level), Ny-lesund, Svalbard, that are recalculated to ambient relative humidity, as well as simultaneous ambient observations with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. To our knowledge, this represents the first study that compares spaceborne lidar measurements to optical aerosol properties from short-term in situ observations (averaged over 5 h) on a case-by-case basis. Finding suitable comparison cases requires an elaborate screening and matching of the CALIOP data with respect to the location of Zeppelin station as well as the selection of temporal and spatial averaging intervals for both the ground-based and spaceborne observations. Reliable reconciliation of these data cannot be achieved with the closest-approach method, which is often used in matching CALIOP observations to those taken at ground sites. This is due to the transport pathways of the air parcels that were sampled. The use of trajectories allowed us to establish a connection between spaceborne and ground-based observations for 57 individual overpasses out of a total of 2018 that occurred in our region of interest around Svalbard (0 to 25 degrees E, 75 to 82 degrees N) in the considered year of 2008. Matches could only be established during winter and spring, since the low aerosol load during summer in connection with the strong solar background and the high occurrence rate of clouds strongly influences the performance and reliability of CALIOP observations. Extinction coefficients in the range of 2 to 130 Mm(-1) at 532 nm were found for successful matches with a difference of a factor of 1.47 (median value for a range from 0.26 to 11.2) between the findings of in situ and spaceborne observations (the latter being generally larger than the former). The remaining difference is likely to be due to the natural variability in aerosol concentration and ambient relative humidity, an insufficient representation of aerosol particle growth, or a misclassification of aerosol type (i.e., choice of lidar ratio) in the CALIPSO retrieval.

  • 33.
    Tunved, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Kulmala, Markku
    Department of Physics, University of Helsinki,.
    Aalto, Pasi
    Department of Physics, University of Helsinki.
    Karlsson, Hans
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Kristensson, Adam
    Division of Nuclear Physics, Lund University.
    Viisanen, Yrjö
    Finnish Meteorological Institute, Helsinki.
    Swietlicki, Erik
    Division of Nuclear Physics, Lund University.
    Dal Maso, Mika
    Department of Physics, University of Helsinki.
    Ström, Johan
    One year boundary layer aerosol size distribution data from five Nordic background stations2003In: Atmospheric Chemistry and Physics, ISSN 1680-7316, Vol. 3, p. 2183-2205Article in journal (Refereed)
  • 34.
    Tunved, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Douglas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Meteorology .
    Kulmala, Markku
    Department of Physics, University of Helsinki.
    Aalto, Pasi
    Department of Physics, University of Helsingfors.
    Viisanen, Yrjö
    Finnish Meteorologic Society.
    Aerosol characteristics of air masses in Northern Europe – influences of location, transport, sinks and sources2005In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, ISSN 0148-0227, Vol. 110, no D7, p. D07201-Article in journal (Refereed)
    Abstract [en]

    Synoptic-scale air masses at different stations were classified following a definition based on Berliner Wetterkarte. This air mass classification has been related to 1 year of aerosol number size distributions measurements performed at four different stations extending from Aspvreten in Sweden (58.8 degrees N) to Pallas in northern Finland (68 degrees N). The air mass classification describes both class of air mass, based on the origin of the air mass, and character of air in terms of marine, mixed, and continental air masses. The aerosol size distribution properties were evaluated in relation to the air masses. Emphasis was put on the differences between marine, mixed, and continental character air masses. It is shown that continental air masses exceed marine and mixed character air masses both in number and mass concentration. Different classes of air masses were further associated with different aerosol size distribution properties. It is also shown that although serving as a somewhat good qualifier for the aerosol at individual stations, the air mass classification cannot be used to estimate the aerosol burden over large geographical areas. Instead, a sharp gradient was shown to exist between different stations, although aerosol properties were observed in equal air masses according to the definition by Berliner Wetterkarte. This gradient manifests as a south-northerly decrease in aerosol total number and volume, indicating that the aerosol properties including the aerosol size distribution are less conservative than the thermodynamic properties (e.g., pseudo-potential temperature and humidity profiles) that characterize the different air masses. Further, using a pseudo-Lagrangian approach, the aerosol turnover time was estimated for different sized aerosols in air moving from south to north (i.e., depletion of aerosols in air arriving from the continent). Turnover time of Aitken particles was found to be in the range of 1-2 days, while accumulation mode turnover time was estimated to be in the order of 2-3 days

  • 35.
    Tunved, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Hans-Christen
    An investigation of processes controlling the evolution of the boundary layer aerosol size distribution properties at the Swedish background station Aspvreten2004In: Atmospheric Chemistry and Physics Discussions, ISSN 1680-7367, Vol. 4, no 4, p. 4507-4543Article in journal (Refereed)
    Abstract [en]

    Aerosol size distributions have been measured at the Swedish background station Aspvreten (58.8° N, 17.4° E). Different states of the aerosol were determined using a novel application of cluster analysis. The analysis resulted in eight different clusters capturing the different stages of the aerosol lifecycle. The aerosol was interpreted as belonging to fresh, intermediate and aged type of size distribution and different magnitudes thereof. With aid of back trajectory analysis we present statistics concerning the relation of source area and different meteorological parameters using a non-lagrangian approach. Source area is argued to be important although not sufficient to describe the observed aerosol properties. Especially processing by clouds and precipitation is shown to be crucial for the evolution of the aerosol size distribution. As much as 60% of the observed size distributions present features likely related to cloud processes or wet deposition. The lifetime properties of different sized aerosols are discussed by means of measured variability. Processing by non-precipitating clouds most obviously affect aerosols in the size range 100 nm and larger. This indicates an approximate limit for activation in clouds to 100 nm in this type of environment. The aerosol lifecycle is discussed. Size distributions bearing signs of recent new particle formation (~30% of the observed size distributions) represent the first stage in the lifecycle. Aging may proceed in two directions: either growth by condensation and coagulation or processing by non-precipitating clouds. In both cases mass is accumulated. Wet removal is the main process capable of removing aerosol mass. Wet deposition is argued to be an important mechanism in reaching a state where nucleation may occur (i.e. sufficiently low aerosol surface area) in environments similar to the one studied

  • 36. Varga, Z.
    et al.
    Kiss, G.
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Modelling the cloud condensation nucleus activity of organic acids on the basis of surface tension and osmolality measurements2007In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 7, no 17, p. 4601-4611Article in journal (Refereed)
    Abstract [en]

    In this study vapour pressure osmometry was used to determine water activity in the solutions of organic acids. The surface tension of the solutions was also monitored in parallel and then Kohler curves were calculated for nine organic acids (oxalic, malonic, succinic, glutaric, adipic, maleic, malic, citric and cis-pinonic). Surface tension depression is negligible for most of the organic acids in dilute (<= 1 w/w%) solutions. Therefore, these compounds affect equilibrium vapour pressure only in the beginning phase of droplet formation when the droplet solution is more concentrated but not necessarily at the critical size. An exception is cis-pinonic acid which remarkably depress surface tension also in dilute (0.1 w/w%) solution and hence at the critical point. The surface tension of organic acid solutions is influenced by the solubility of the compound, the length of the carbon chain and also by the polar functional groups present in the molecule. Similarly to surface tension solubility plays an important role also in water activity: compounds with higher solubility (e.g. malonic, maleic and glutaric acid) reduce water activity significantly in the early phase of droplet formation while less soluble acids (e.g. succinic and adipic acid) are saturated in small droplets and the solution starts diluting only in bigger droplets. As a consequence, compounds with lower solubility have a minor effect on water activity in the early phase of droplet formation. To deduce the total effect Kohler curves were calculated and critical supersaturations (S-c) were determined for the organic acids using measured surface tension and water activity. It was found that critical supersaturation grew with growing carbon number. Oxalic acid had the lowest critical supersaturation in the size range studied and it was comparable to the activation of ammonium sulphate. The S-c values obtained in this study were compared to data from CCNC experiments. In most cases good agreement was found. For modelling purposes S-c vs. d(dry) plots are given and the dependence of water activity and surface tension on concentration are also formulated.

  • 37.
    Wallén, Anna
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Lidén, Göran
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Hans-Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Measured elemental carbon by thermo-optical transmittance analysis in water-soluble extracts from diesel exhaust, woodsmoke, and ambient particulate samples2010In: Journal of Occupational and Environmental Hygiene, ISSN 1545-9624, E-ISSN 1545-9632, Vol. 7, no 1, p. 35-45Article in journal (Refereed)
    Abstract [en]

    Elemental carbon has been proposed as a marker of diesel particulate matter. The objective of this study was to investigate if water-soluble carbonaceous compounds could be responsible for positive bias of elemental carbon using NIOSH Method 5040 with a thermo-optical carbon transmittance analyzer. Filter samples from eight different aerosol environments were used: pure diesel exhaust fume with a high content of elemental carbon, pure diesel exhaust fume with a low content of elemental carbon, pure biodiesel exhaust fume, pure woodsmoke, an urban road tunnel, an urban street canyon, an urban background site, and residential woodburning in an urban area. Part of each filter sample was analyzed directly with a thermo-optical carbon analyzer, and another part was extracted with water. This water-soluble extract was filtered to remove particles, spiked onto filter punches, and analyzed with a thermo-optical transmittance carbon analyzer. The ratio of elemental carbon in the water-soluble extract to the particulate sample measurement was 18, 12, and 7%, respectively, for the samples of pure woodsmoke, residential woodburning, and urban background. Samples with diesel particulate matter and ambient samples with motor exhaust detected no elemental carbon in the water-soluble extract. Since no particles were present in the filtered water-soluble extract, part of the water-soluble organic carbon species, existing or created during analysis, are misclassified as elemental carbon with this analysis. The conclusion is that in measuring elemental carbon in particulate aerosol samples with thermo-optical transmittance analysis, woodsmoke, and biomass combustion samples show a positive bias of elemental carbon. The water-soluble EC could be used as a simple method to indicate other sources, such as wood or other biomass combustion aerosol particles.

  • 38. Yttri, K. E.
    et al.
    Aas, W.
    Bjerke, A.
    Cape, J. N.
    Cavalli, F.
    Ceburnis, D.
    Dye, C.
    Emblico, L.
    Facchini, M. C.
    Forster, C.
    Hanssen, J. E.
    Hansson, Hans Christen
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Jennings, S. G.
    Maenhaut, W.
    Putaud, J. P.
    Torseth, K.
    Elemental and organic carbon in PM10: a one year measurement campaign within the European Monitoring and Evaluation Programme EMEP2007In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 7, no 22, p. 5711-5725Article in journal (Refereed)
    Abstract [en]

    In the present study, ambient aerosol (PM10) concentrations of elemental carbon (EC), organic carbon (OC), and total carbon (TC) are reported for 12 European rural background sites and two urban background sites following a one-year (1 July 2002 & ndash;1 July 2003) sampling campaign within the European Monitoring and Evaluation Programme, EMEP (http://www.emep.int/). The purpose of the campaign was to assess the feasibility of performing EC and OC monitoring on a regular basis and to obtain an overview of the spatial and seasonal variability on a regional scale in Europe. Analyses were performed using the thermal-optical transmission (TOT) instrument from Sunset Lab Inc., operating according to a NIOSH derived temperature program. The annual mean mass concentration of EC ranged from 0.17 +/- 0.19 mu G m(-3) (mean +/- SD) at Birkenes (Norway) to 1.83 +/- 1.32 mu g m(-3) at Ispra (Italy). The corresponding range for OC was 1.20 +/- 1.29 mu g m(-3) at Mace Head (Ireland) to 7.79 +/- 6.80 mu g m-3 at Ispra. On average, annual concentrations of EC, OC, and TC were three times higher for rural background sites in Central, Eastern and Southern Europe compared to those situated in the Northern and Western parts of Europe. Wintertime concentrations of EC and OC were higher than those recorded during summer for the majority of the sites. Moderate to high Pearson correlation coefficients (r(p)) (0.50-0.94) were observed for EC versus OC for the sites investigated. The lowest correlation coefficients were noted for the three Scandinavian sites: Aspvreten (SE), Birkenes (NO), and Virolahti (FI), and the Slovakian site Stara Lesna, and are suggested to reflect biogenic sources, wild and prescribed fires. This suggestion is supported by the fact that higher concentrations of OC are observed for summer compared to winter for these sites. For the rural background sites, total carbonaceous material accounted for 30 +/- 9% of PM10, of which 27 +/- 9% could be attributed to organic matter (OM) and 3.4 +/- 1.0% to elemental matter (EM). OM was found to be more abundant than SO42- for sites reporting both parameters.

1 - 38 of 38
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