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  • 1. 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.

  • 2. Backman, John
    et al.
    Schmeisser, Lauren
    Virkkula, Aki
    Ogren, John A.
    Asmi, Eija
    Starkweather, Sandra
    Sharma, Sangeeta
    Eleftheriadis, Konstantinos
    Uttal, Taneil
    Jefferson, Anne
    Bergin, Michael
    Makshtas, Alexander
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Fiebig, Markus
    On Aethalometer measurement uncertainties and an instrument correction factor for the Arctic2017In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 10, no 12, p. 5039-5062Article in journal (Refereed)
    Abstract [en]

    Several types of filter-based instruments are used to estimate aerosol light absorption coefficients. Two significant results are presented based on Aethalometer measurements at six Arctic stations from 2012 to 2014. First, an alternative method of post-processing the Aethalometer data is presented, which reduces measurement noise and lowers the detection limit of the instrument more effectively than box-car averaging. The biggest benefit of this approach can be achieved if instrument drift is minimised. Moreover, by using an attenuation threshold criterion for data post-processing, the relative uncertainty from the electronic noise of the instrument is kept constant. This approach results in a time series with a variable collection time (Delta t) but with a constant relative uncertainty with regard to electronic noise in the instrument. An additional advantage of this method is that the detection limit of the instrument will be lowered at small aerosol concentrations at the expense of temporal resolution, whereas there is little to no loss in temporal resolution at high aerosol concentrations (>2.1-6.7Mm(-1) as measured by the Aethalometers). At high aerosol concentrations, minimising the detection limit of the instrument is less critical. Additionally, utilising co-located filter-based absorption photometers, a correction factor is presented for the Arctic that can be used in Aethalometer corrections available in literature. The correction factor of 3.45 was calculated for low-elevation Arctic stations. This correction factor harmonises Aethalometer attenuation coefficients with light absorption coefficients as measured by the co-located light absorption photometers. Using one correction factor for Arctic Aethalometers has the advantage that measurements between stations become more inter-comparable.

  • 3. Bisht, D. S.
    et al.
    Tiwari, S.
    Dumka, U. C.
    Srivastava, A. K.
    Safai, P. D.
    Ghude, S. D.
    Chate, D. M.
    Rao, P. S. P.
    Ali, K.
    Prabhakaran, T.
    Panickar, A. S.
    Soni, V. K.
    Attri, S. D.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Chakrabarty, R. K.
    Hopke, P. K.
    Tethered balloon-born and ground-based measurements. of black carbon and particulate profiles within the lower troposphere during the foggy period in Delhi, India2016In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 573, p. 894-905Article in journal (Refereed)
    Abstract [en]

    The ground and vertical profiles of particulate matter (PM) were mapped as part of a pilot study using a Tethered balloon within the lower troposphere (1000 m) during the foggy episodes in the winter season of 2015-16 in New Delhi, India. Measurements of black carbon (BC) aerosol and PM <2.5 and 10 mu m (PM2.5 &PM-10 respectively) concentrations and their associated particulate optical properties along with meteorological parameters were made. The mean concentrations of PM2.5, PM10, BC370 (nm), and BC880 nm were observed to be 146.8 +/- 42.1, 245.4 +/- 65.4, 30.3 +/- 122, and 24.1 +/- 103 mu g m(-3), respectively. The mean value of PM2.5 was similar to 12 times higher than the annual US-EPA air quality standard. The fraction of BC in PM2.5 that contributed to absorption in the shorter visible wavelengths (BC370 nm) was-21%. Compared to clear days, the ground level mass concentrations of PM2.5 and BC370 nm particles were substantially increased (59% and 24%, respectively) during the foggy episode. The aerosol light extinction coefficient (sigma(ext)) value was much higher (mean: 610 Mm(-1)) during the lower visibility (foggy) condition. Higher concentrations of PM2.5 (89 mu g m(-3)) and longer visible wavelength absorbing BC880 am (25.7 mu g m(-3)) particles were observed up to 200 m. The BC880 nm and PM2.5 aerosol concentrations near boundary layer (1 km) were significantly higher (similar to 1.9 and 12 mu g m(-3)), respectively. The BC (i.e BCtot) aerosol direct radiative forcing (DRF) values were estimated at the top of the atmosphere (TOA), surface (SFC), and atmosphere (ATM) and its resultant forcing were- 75.5 Wm(-2) at SFC indicating the cooling effect at the surface. A positive value (20.9 Wm(-2)) of BC aerosol DRF at TOA indicated the warming effect at the top of the atmosphere over the study region. The net DRF value due to BC aerosol was positive (96.4 Wm(-2)) indicating a net warming effect in the atmosphere. The contribution of fossil and biomass fuels to the observed BC aerosol DRF values was -78% and-22%, respectively. The higher mean atmospheric heating rate (2.71 K clay(-1)) by BC aerosol in the winter season would probably strengthen the temperature inversion leading to poor dispersion and affecting the formation of clouds. Serious detrimental impacts on regional climate due to the high concentrations of BC and PM (especially PM2.5) aerosol are likely based on this study and suggest the need for immediate, stringent measures to improve the regional air quality in the northern India.

  • 4. Croft, Betty
    et al.
    Martin, Randall V.
    Leaitch, W. Richard
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Breider, Thomas J.
    D'Andrea, Stephen D.
    Pierce, Jeffrey R.
    Processes controlling the annual cycle of Arctic aerosol number and size distributions2016In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 16, no 6, p. 3665-3682Article in journal (Refereed)
    Abstract [en]

    Measurements at high-Arctic sites (Alert, Nunavut, and Mt. Zeppelin, Svalbard) during the years 2011 to 2013 show a strong and similar annual cycle in aerosol number and size distributions. Each year at both sites, the number of aerosols with diameters larger than 20 nm exhibits a minimum in October and two maxima, one in spring associated with a dominant accumulation mode (particles 100 to 500 nm in diameter) and a second in summer associated with a dominant Aitken mode (particles 20 to 100 nm in diameter). Seasonal-mean aerosol effective diameter from measurements ranges from about 180 in summer to 260 nm in winter. This study interprets these annual cycles with the GEOS-Chem-TOMAS global aerosol microphysics model. Important roles are documented for several processes (new-particle formation, coagulation scavenging in clouds, scavenging by precipitation, and transport) in controlling the annual cycle in Arctic aerosol number and size. Our simulations suggest that coagulation scavenging of interstitial aerosols in clouds by aerosols that have activated to form cloud droplets strongly limits the total number of particles with diameters less than 200 nm throughout the year. We find that the minimum in total particle number in October can be explained by diminishing new-particle formation within the Arctic, limited transport of pollution from lower latitudes, and efficient wet removal. Our simulations indicate that the summertime-dominant Aitken mode is associated with efficient wet removal of accumulation-mode aerosols, which limits the condensation sink for condensable vapours. This in turn promotes new-particle formation and growth. The dominant accumulation mode during spring is associated with build up of transported pollution from outside the Arctic coupled with less-efficient wet-removal processes at colder temperatures. We recommend further attention to the key processes of new-particle formation, interstitial coagulation, and wet removal and their delicate interactions and balance in size-resolved aerosol simulations of the Arctic to reduce uncertainties in estimates of aerosol radiative effects on the Arctic climate.

  • 5. 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.

  • 6. 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.

  • 7. 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.

  • 8. Evangeliou, N.
    et al.
    Balkanski, Y.
    Hao, W. M.
    Petkov, A.
    Silverstein, R. P.
    Corley, R.
    Nordgren, B. L.
    Urbanski, S. P.
    Eckhardt, S.
    Stohl, A.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Crepinsek, S.
    Jefferson, A.
    Sharma, S.
    Nojgaard, J. K.
    Skov, H.
    Wildfires in northern Eurasia affect the budget of black carbon in the Arctic - a 12-year retrospective synopsis (2002-2013)2016In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 16, no 12, p. 7587-7604Article in journal (Refereed)
    Abstract [en]

    In recent decades much attention has been given to the Arctic environment, where climate change is happening rapidly. Black carbon (BC) has been shown to be a major component of Arctic pollution that also affects the radiative balance. In the present study, we focused on how vegetation fires that occurred in northern Eurasia during the period of 2002-2013 influenced the budget of BC in the Arctic. For simulating the transport of fire emissions from northern Eurasia to the Arctic, we adopted BC fire emission estimates developed independently by GFED3 (Global Fire Emissions Database) and FEI-NE (Fire Emission Inventory - northern Eurasia). Both datasets were based on fire locations and burned areas detected by MODIS (Moderate resolution Imaging Spectroradiometer) instruments on NASA's (National Aeronautics and Space Administration) Terra and Aqua satellites. Anthropogenic sources of BC were adopted from the MACCity (Monitoring Atmospheric Composition and Climate and megacity Zoom for the Environment) emission inventory. During the 12-year period, an average area of 250aEuro-000aEuro-km(2)aEuro-yr(-1) was burned in northern Eurasia (FEI-NE) and the global emissions of BC ranged between 8.0 and 9.5aEuro-TgaEuro-yr(-1) (FEI-NE+MACCity). For the BC emitted in the Northern Hemisphere (based on FEI-NE+MACCity), about 70aEuro-% originated from anthropogenic sources and the rest from biomass burning (BB). Using the FEI-NE+MACCity inventory, we found that 102aEuro-+/- aEuro-29aEuro-ktaEuro-yr(-1) BC was deposited in the Arctic (defined here as the area north of 67A degrees aEuro-N) during the 12 years simulated, which was twice as much as when using the MACCity inventory (56aEuro-+/- aEuro-8aEuro-ktaEuro-yr(-1)). The annual mass of BC deposited in the Arctic from all sources (FEI-NE in northern Eurasia, MACCity elsewhere) is significantly higher by about 37aEuro-% in 2009 (78 vs. 57aEuro-ktaEuro-yr(-1)) to 181aEuro-% in 2012 (153 vs. 54aEuro-ktaEuro-yr(-1)), compared to the BC deposited using just the MACCity emission inventory. Deposition of BC in the Arctic from BB sources in the Northern Hemisphere thus represents 68aEuro-% of the BC deposited from all BC sources (the remaining being due to anthropogenic sources). Northern Eurasian vegetation fires (FEI-NE) contributed 85aEuro-% (79-91aEuro-%) to the BC deposited over the Arctic from all BB sources in the Northern Hemisphere. We estimate that about 46aEuro-% of the BC deposited over the Arctic from vegetation fires in northern Eurasia originated from Siberia, 6aEuro-% from Kazakhstan, 5aEuro-% from Europe, and about 1aEuro-% from Mongolia. The remaining 42aEuro-% originated from other areas in northern Eurasia. About 42aEuro-% of the BC released from northern Eurasian vegetation fires was deposited over the Arctic (annual average: 17aEuro-%) during spring and summer.

  • 9.
    Franke, Vera
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Swedish University of Agricultural Sciences, Sweden.
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Wideqvist, Ulla
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Acosta Navarro, Juan Camilo
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Barcelona Supercomputing Center, Spain.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Rosati, Bernadette
    Gysel, Martin
    Salter, Matthew Edward
    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.
    Chemical composition and source analysis of carbonaceous aerosol particles at a mountaintop site in central Sweden2017In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 69, article id 1353387Article in journal (Refereed)
    Abstract [en]

    The chemical composition of atmospheric particulate matter at Mt. angstrom reskutan, a mountaintop site in central Sweden, was analysed with a focus on its carbonaceous content. Filter samples taken during the Cloud and Aerosol Experiment at angstrom re (CAEsAR 2014) were analysed by means of a thermo-optical method and ion chromatography. Additionally, the particle light absorption and particle number size distribution measurements for the entire campaign were added to the analysis. Mean airborne concentrations of organic and elemental carbon during CAEsAR 2014 were OC= 0.85 +/- 0.8 mu gm(-3) and EC = 0.06 +/- 0.06 mu gm(-3), respectively. Elemental to organic carbon ratios varied between EC/OC = 0.02 and 0.19. During the study a large wildfire occurred in Vastmanland, Sweden, with the plume reaching our study site. This led to significant increases in OC and EC concentrations (OC = 3.04 +/- 0.03 mu gm(-3) and EC = 0.24 +/- 0.00 mu gm(-3)). The mean mass-specific absorption coefficient observed during the campaign was sigma(BC)(abs) = 9.1 +/- 7.3 m(2)g(-1) (at wavelength lambda= 637 nm). In comparison to similarly remote European sites, Mt. angstrom reskutan experienced significantly lower carbonaceous aerosol loadings with a clear dominance of organic carbon. A mass closure study revealed a missing chemical mass fraction that likely originated from mineral dust. Potential regional source contributions of the carbonaceous aerosol were investigated using modelled air mass back trajectories. This source apportionment pointed to a correlation between high EC concentrations and air originating from continental Europe. Particles rich in organic carbon most often arrived from highly vegetated continental areas. However, marine regions were also a source of these aerosol particles. The source contributions derived during this study were compared to emission inventories of an Earth system model. This comparison highlighted a lack of OC and EC point-sources in the model's emission inventory which could potentially lead to an underestimation of the carbonaceous aerosol reaching Mt. angstrom reskutan in the simulation of this Earth system model.

  • 10.
    Freud, E.
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Strom, J.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Rosenfeld, D.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Swietlicki, E.
    Anthropogenic aerosol effects on convective cloud microphysical properties in southern Sweden2008In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 60, no 2, p. 286-297Article in journal (Refereed)
    Abstract [en]

    In this study, we look for anthropogenic aerosol effects in southern Scandinavia's clouds under the influence of moderate levels of pollution and relatively weak dynamic forcing. This was done by comparing surface aerosol measurements with convective cloud microphysical profiles produced from satellite image analyses. The results show that the clouds associated with the anthropogenic-affected air with high PM0.5, had to acquire a vertical development of similar to 3.5 km before forming precipitation-sized particles, compared to less than 1 km for the clouds associated with low PM0.5 air-masses. Additionally, a comparison of profiles with precipitation was done with regard to different potentially important parameters. For precipitating clouds the variability of the cloud thickness needed to produce the precipitation (Delta h(14)) is directly related to PM0.5 concentrations, even without considering atmospheric stability, the specific aerosol size distribution or the aerosols' chemical composition. Each additional 1 mu g m(-3) of PM0.5 was found to increase Delta h(14) by similar to 200-250 m. Our conclusion is that it is indeed possible to detect the effects of anthropogenic aerosol on the convective clouds in southern Scandinavia despite modest aerosol masses. It also emphasizes the importance of including aerosol processes in climate-radiation models and in numerical weather prediction models.

  • 11. Freud, E.
    et al.
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Rosenfeld, D.
    Tunved,
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Swietlicki, E.
    Anthropogenic aerosol effects on convective cloud microphysical properties in southern Sweden2007In: Tellus BArticle in journal (Refereed)
  • 12.
    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.

  • 13. Giamarelou, Maria
    et al.
    Eleftheriadis, Konstantinos
    Nyeki, Stephan
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Torseth, Kjetil
    Biskos, George
    Indirect evidence of the composition of nucleation mode atmospheric particles in the high Arctic2016In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 121, no 2, p. 965-975Article in journal (Refereed)
    Abstract [en]

    Previous long-term observations have shown that nanoparticle formation events are common in the summer-time high Arctic and linked to local photochemical activity. However, current knowledge is limited with respect to the chemical precursors of resulting nanoparticles and the compounds involved in their subsequent growth. Here we report case-study measurements during new particle formation (NPF) events of the particle size distribution (diameter>7nm) and for the first time the volatility of monodisperse particles having diameter 40nm, providing indirect information about their composition. Volatility measurements provide indirect evidence that a predominant fraction of the 12nm particle population is ammoniated sulfates in the summertime high Arctic. Our observations further suggest that the majority of the sub-40nm particle population during NPF events does not exist in the form of sulfuric acid but rather as partly or fully neutralized ammoniated sulfates.

  • 14.
    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).

  • 15.
    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.

  • 16. 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.

  • 17. Heintzenberg, J.
    et al.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Potential source regions and processes of aerosol in the summer Arctic2015In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 15, no 11, p. 6487-6502Article in journal (Refereed)
    Abstract [en]

    Sub-micrometer particle size distributions measured during four summer cruises of the Swedish icebreaker Oden 1991, 1996, 2001, and 2008 were combined with dimethyl sulfide gas data, back trajectories, and daily maps of pack ice cover in order to investigate source areas and aerosol formation processes of the boundary layer aerosol in the central Arctic. With a clustering algorithm, potential aerosol source areas were explored. Clustering of particle size distributions together with back trajectories delineated five potential source regions and three different aerosol types that covered most of the Arctic Basin: marine, newly formed and aged particles over the pack ice. Most of the pack ice area with <15% of open water under the trajectories exhibited the aged aerosol type with only one major mode around 40 nm. For newly formed particles to occur, two conditions had to be fulfilled over the pack ice: the air had spent 10 days while traveling over ever more contiguous ice and had traveled over less than 30% open water during the last 5 days. Additionally, the air had experienced more open water (at least twice as much as in the cases of aged aerosol) during the last 4 days before arrival in heavy ice conditions at Oden. Thus we hypothesize that these two conditions were essential factors for the formation of ultrafine particles over the central Arctic pack ice. In a comparison the Oden data with summer size distribution data from Alert, Nunavut, and Mt. Zeppelin, Spitsbergen, we confirmed the Oden findings with respect to particle sources over the central Arctic. Future more frequent broken-ice or open water patches in summer will spur biological activity in surface water promoting the formation of biological particles. Thereby low clouds and fogs and subsequently the surface energy balance and ice melt may be affected.

  • 18. Heintzenberg, Jost
    et al.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Gali, Martí
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    New particle formation in the Svalbard region 2006-20152017In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 17, no 10, p. 6153-6175Article in journal (Refereed)
    Abstract [en]

    Events of new particle formation (NPF) were analyzed in a 10-year data set of hourly particle size distributions recorded on Mt. Zeppelin, Spitsbergen, Svalbard. Three different types of NPF events were identified through objective search algorithms. The first and simplest algorithm utilizes short-term increases in particle concentrations below 25 nm (PCT (percentiles) events). The second one builds on the growth of the sub-50 nm diameter median (DGR (diameter growth) events) and is most closely related to the classical banana type of event. The third and most complex, multiple-size approach to identifying NPF events builds on a hypothesis suggesting the concurrent production of polymer gel particles at several sizes below ca. 60 nm (MEV (multisize growth) events). As a first and general conclusion, we can state that NPF events are a summer phenomenon and not related to Arctic haze, which is a late winter to early spring feature. The occurrence of NPF events appears to be somewhat sensitive to the available data on precipitation. The seasonal distribution of solar flux suggests some photochemical control that may affect marine biological processes generating particle precursors and/or atmospheric photochemical processes that generate condensable vapors from precursor gases. Notably, the seasonal distribution of the biogenic methanesulfonate (MSA) follows that of the solar flux although it peaks before the maxima in NPF occurrence. A host of ancillary data and findings point to varying and rather complex marine biological source processes. The potential source regions for all types of new particle formation appear to be restricted to the marginal-ice and open-water areas between northeastern Greenland and eastern Svalbard.Depending on conditions, yet to be clarified new particle formation may become visible as short bursts of particles around 20 nm (PCT events), longer events involving condensation growth (DGR events), or extended events with elevated concentrations of particles at several sizes below 100 nm (MEV events). The seasonal distribution of NPF events peaks later than that of MSA and DGR, and in particular than that of MEV events, which reach into late summer and early fall with open, warm, and biologically active waters around Svalbard. Consequently, a simple model to describe the seasonal distribution of the total number of NPF events can be based on solar flux and sea surface temperature, representing environmental conditions for marine biological activity and condensation sink, controlling the balance between new particle nucleation and their condensational growth. Based on the sparse knowledge about the seasonal cycle of gel-forming marine microorganisms and their controlling factors, we hypothesize that the seasonal distribution of DGR and, more so, MEV events reflect the seasonal cycle of the gel-forming phytoplankton.

  • 19. Hoffmann, Anne
    et al.
    Osterloh, Lukas
    Stone, Robert
    Lampert, Astrid
    Ritter, Christoph
    Stock, Maria
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hennig, Tabea
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Boeckmann, Christine
    Li, Shao-Meng
    Eleftheriadis, Kostas
    Maturilli, Marion
    Orgis, Thomas
    Herber, Andreas
    Neuber, Roland
    Dethloff, Klaus
    Remote sensing and in situ measurements of tropospheric aerosol, a pamarcmip case study2012In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 52, p. 56-66Article in journal (Refereed)
    Abstract [en]

    In this work, a closure experiment for tropospheric aerosol is presented. Aerosol size distributions and single scattering albedo from remote sensing data are compared to those measured in-situ. An aerosol pollution event on 4 April 2009 was observed by ground based and airborne lidar and photometer in and around Ny-Alesund, Spitsbergen, as well as by DMPS, nephelometer and particle soot absorption photometer at the nearby Zeppelin Mountain Research Station. The presented measurements were conducted in an area of 40 x 20 km around Ny-Alesund as part of the 2009 Polar Airborne Measurements and Arctic Regional Climate Model Simulation Project (PAMARCMiP). Aerosol mainly in the accumulation mode was found in the lower troposphere, however, enhanced backscattering was observed up to the tropopause altitude. A comparison of meteorological data available at different locations reveals a stable multi-layer-structure of the lower troposphere. It is followed by the retrieval of optical and microphysical aerosol parameters. Extinction values have been derived using two different methods, and it was found that extinction (especially in the UV) derived from Raman lidar data significantly surpasses the extinction derived from photometer AOD profiles. Airborne lidar data shows volume depolarization values to be less than 2.5% between 500 m and 2.5 km altitude, hence, particles in this range can be assumed to be of spherical shape. In-situ particle number concentrations measured at the Zeppelin Mountain Research Station at 474 m altitude peak at about 0.18 mu m diameter, which was also found for the microphysical inversion calculations performed at 850 m and 1500 m altitude. Number concentrations depend on the assumed extinction values, and slightly decrease with altitude as well as the effective particle diameter. A low imaginary part in the derived refractive index suggests weakly absorbing aerosols, which is confirmed by low black carbon concentrations, measured at the Zeppelin Mountain as well as on board the Polar 5 aircraft.

  • 20. 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.

  • 21. 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.

  • 22. Lihavainen, Heikki
    et al.
    Kerminen, Veli-Matti
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Aaltonen, Veijo
    Arola, Antti
    Hatakka, Juha
    Hyvärinen, Antti
    Viisanen, Yrjö
    Observational signature of the direct radiative effect by natural boreal forest aerosols and its relation to the corresponding first indirect effect2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114Article in journal (Other academic)
    Abstract [en]

    By using a screened set of long-term aerosol measurement data, the contribution of natural boreal forest aerosols to the direct radiative effect (DRE) was observed at a remote continental site in northern Finland. Averaged over the summer season, the magnitude of this effect at the top of the atmosphere was estimated to be in the range -(0.37-0.74) W m(-2) in our study region and possibly somewhat higher over the whole boreal forest region. Globally, the DRE owing to boreal forest aerosols is much smaller than that owing to natural sea salt or dust aerosols, as well as direct radiative forcing by anthropogenic aerosols. We also updated the earlier estimates of the first indirect radiative effect (IRE) by natural boreal forest aerosols. We found that this IRE is likely to be substantially higher, perhaps more than an order of magnitude, than the corresponding DRE

  • 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.
    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.

  • 25. Mossberg Sonnek, Karin
    et al.
    Mårtensson, Tomas
    Veiback, Ester
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Grahn, Håkan
    von Schoenberg, Pontus
    Brännström, Niklas
    Bucht, Anders
    The impacts of a Laki-like eruption on the present Swedish society2017In: Natural Hazards, ISSN 0921-030X, E-ISSN 1573-0840, Vol. 88, no 3, p. 1565-1590Article in journal (Refereed)
    Abstract [en]

    In this study, we analyse and discuss the possible impacts on the Swedish society of a volcanic eruption on Iceland, emitting ash particles and large quantities of sulphur dioxide. A scenario was developed, based on the historical Laki eruption of 1783-1784, to describe the content of a potential sulphur fog over time in Sweden. Due to its high complexity and the many uncertainties in the underpinning scientific data, the scenario was developed using a cross-disciplinary approach incorporating experts from different scientific fields. An analysis of the impacts of the hazard on human health, environment and technical equipment was then performed and, finally, representatives from national authorities assessed the overall societal challenges in responding to the consequences of a massive volcanic eruption. The analysis shows that it is the peak concentrations of sulphur dioxide and sulphuric acid rather than the longer periods of moderate concentrations that contribute most to the negative consequences for human health and environment. Altogether, three societal challenges were identified: the ability to compile and disseminate relevant information fast enough, to perform continuous measurements of concentrations of different substances in affected areas and to meet the large demand for medical care.

  • 26.
    Mårtensson, E. Monica
    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).
    Korhonen, Hannele
    Nilsson, E. Douglas
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    The role of sea-salt emissions in controlling the marine Aitken and accumulation mode aerosol: a model study2010In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 62, no 4, p. 259-279Article in journal (Refereed)
    Abstract [en]

    The remote marine aerosol and the cloud droplet number concentration (CDNC) are examined with an aerosol microphysics box model in an attempt to better understand the processes involved in the formation and transformation of the marine aerosol. Emission of submicrometre sea-salt and dimethylsulfide (DMS) have been included together with aerosol dynamics, gas and liquid phase chemistry and cloud processing representative for the marine boundary layer atmosphere. Our simulations are able to reproduce a bimodal submicrometre size distribution with realistic number concentrations even when new particle formation by nucleation is neglected. This indicates that ultrafine primary sea-salt flux is an important source of Aitken mode particles and CDNC. However, sulphate still constitutes 20-80% of the Aitken and accumulation mode masses. The temperature dependence of the sea-salt source function leads to a 23% decrease in total number concentration when the temperature increases from 12 to 20 degrees C. The influence of DMS emission on the aerosol and CDNC is minimal but the size distribution and mass concentration of sulphate is changed, mostly due to in-cloud processes. The wind speed is the dominant factor determining the CDNC, although entrainment of aerosols from free troposphere can have a substantial effect.

  • 27.
    Mårtensson, M
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Tunved, P
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Korhonen, H.
    Nilsson, D
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Are submicrometer sea salt emission parameterisations consistent with observed remote marine aerosol distributions?2008In: European Aerosol Conference, EAC 2008: August 24-29, Thessaloniki, Greece, 2008Conference paper (Refereed)
  • 28.
    Partridge, Daniel G.
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Vrugt, J. A.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ekman, A. M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gorea, D.
    Univ Amsterdam, Inst Biodivers & Ecosyst Dynam, Amsterdam, Netherlands .
    Sorooshian, A.
    Univ Arizona, Dept Chem & Environm Engn, Tucson, AZ USA .
    Inverse modeling of cloud-aerosol interactions: Part 1: Detailed response surface analysis2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 14, p. 7269-7287Article in journal (Refereed)
    Abstract [en]

    New methodologies are required to probe the sensitivity of parameters describing cloud droplet activation. This paper presents an inverse modeling-based method for exploring cloud-aerosol interactions via response surfaces. The objective function, containing the difference between the measured and model predicted cloud droplet size distribution is studied in a two-dimensional framework, and presented for pseudo-adiabatic cloud parcel model parameters that are pair-wise selected. From this response surface analysis it is shown that the susceptibility of cloud droplet size distribution to variations in different aerosol physiochemical parameters is highly dependent on the aerosol environment and meteorological conditions. In general the cloud droplet size distribution is most susceptible to changes in the updraft velocity. A shift towards an increase in the importance of chemistry for the cloud nucleating ability of particles is shown to exist somewhere between marine average and rural continental aerosol regimes. We also use these response surfaces to explore the feasibility of inverse modeling to determine cloud-aerosol interactions. It is shown that the "cloud-aerosol" inverse problem is particularly difficult to solve due to significant parameter interaction, presence of multiple regions of attraction, numerous local optima, and considerable parameter insensitivity. The identifiability of the model parameters will be dependent on the choice of the objective function. Sensitivity analysis is performed to investigate the location of the information content within the calibration data to confirm that our choice of objective function maximizes information retrieval from the cloud droplet size distribution. Cloud parcel models that employ a moving-centre based calculation of the cloud droplet size distribution pose additional difficulties when applying automatic search algorithms for studying cloud-aerosol interactions. To aid future studies, an increased resolution of the region of the size spectrum associated with droplet activation within cloud parcel models, or further development of fixed-sectional cloud models would be beneficial. Despite these improvements, it is demonstrated that powerful search algorithms remain necessary to efficiently explore the parameter space and successfully solve the cloud-aerosol inverse problem.

  • 29.
    Partridge, Daniel G.
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Vrugt, J. A.
    Univ Calif Irvine, Dept Civil & Environm Engn, Henry Samueli Sch Engn, Irvine, CA USA .
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ekman, Annica
    Stockholm University, Faculty of Science, Department of Meteorology .
    Struthers, Hamish
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Department of Meteorology .
    Sorooshian, A.
    Univ Arizona, Dept Atmospher Sci, Tucson, AZ USA .
    Inverse modeling of cloud-aerosol interactions: Part 2: Sensitivity tests on liquid phase clouds using a Markov Chain Monte carlo based simulation approach2012In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, no 6, p. 2823-2847Article in journal (Refereed)
    Abstract [en]

    This paper presents a novel approach to investigate cloud-aerosol interactions by coupling a Markov Chain Monte Carlo (MCMC) algorithm to a pseudo-adiabatic cloud parcel model. Despite the number of numerical cloud-aerosol sensitivity studies previously conducted few have used statistical analysis tools to investigate the sensitivity of a cloud model to input aerosol physiochemical parameters. Using synthetic data as observed values of cloud droplet number concentration (CDNC) distribution, this inverse modelling framework is shown to successfully converge to the correct calibration parameters. The employed analysis method provides a new, integrative framework to evaluate the sensitivity of the derived CDNC distribution to the input parameters describing the lognormal properties of the accumulation mode and the particle chemistry. To a large extent, results from prior studies are confirmed, but the present study also provides some additional insightful findings. There is a clear transition from very clean marine Arctic conditions where the aerosol parameters representing the mean radius and geometric standard deviation of the accumulation mode are found to be most important for determining the CDNC distribution to very polluted continental environments (aerosol concentration in the accumulation mode >1000 cm−3) where particle chemistry is more important than both number concentration and size of the accumulation mode. The competition and compensation between the cloud model input parameters illustrate that if the soluble mass fraction is reduced, both the number of particles and geometric standard deviation must increase and the mean radius of the accumulation mode must increase in order to achieve the same CDNC distribution. For more polluted aerosol conditions, with a reduction in soluble mass fraction the parameter correlation becomes weaker and more non-linear over the range of possible solutions (indicative of the sensitivity). This indicates that for the cloud parcel model used herein, the relative importance of the soluble mass fraction appears to decrease if the number or geometric standard deviation of the accumulation mode is increased. This study demonstrates that inverse modelling provides a flexible, transparent and integrative method for efficiently exploring cloud-aerosol interactions efficiently with respect to parameter sensitivity and correlation.

  • 30.
    Partridge, Daniel
    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).
    Vrugt, Jasper
    Ekman, Annica
    Stockholm University, Faculty of Science, Department of Meteorology .
    Sorooshian, Armin
    Roelofs, Geert-Jan
    Jonsson, Haf
    A study of marine stratocumulus clouds using an inverse modelling approachManuscript (preprint) (Other academic)
    Abstract [en]

    This paper presents a Bayesian inverse modelling approach to simultaneously assess the ability of a pseudo-adiabatic cloud parcel model to match in-situ measurements of the droplet size distribution in a cloud as well as model parameters describing the updraft and different aerosol microphysical properties (herein termed calibration parameters). Our methodology is tested using observations from two clean (average accumulation mode number concentration < 60 cm-3) and two polluted clouds (average accumulation mode number concentration > 100 cm-3) observed during the Marine Stratus/Stratocumulus Experiment (MASE II) campaign. Our framework capitalizes on recent developments in Markov Chain Monte Carlo (MCMC) simulation and retrieves the most likely parameter values and their underlying posterior probability density function. This distribution provides necessary information to efficiently and in a statistically robust manner, assess both the global sensitivity of aerosol physiochemical and meteorological parameters, and the suitability of cloud parcel models to comprehensively describe the evolution of cloud droplet size distributions in stratocumulus clouds.

    We demonstrate that the updraft velocity is the most important calibration parameter for describing the observed droplet distribution for each cloud case, corroborating previous findings. The accumulation mode number, shape and size are found to be more important than chemistry except for the most polluted conditions (average accumulation mode number concentration ~455 cm-3). This highlights that conditions exist for marine stratocumulus clouds in which an accurate description of the aerosol chemistry is a pre-requisite for the accurate representation of cloud microphysical properties.

    Overall, the MCMC algorithm successfully matches the observed droplet size distribution for each cloud case. In doing so, however, the subsequent agreement between the derived and measured calibration parameters is generally poor. An important result from this analysis is that for certain calibration parameters, consistent patterns of deviation were found in the posterior distributions for all the clouds included in this study. This finding indicates that either there is systematic sampling or averaging artefacts in our observations, or our pseudo-adiabatic cloud parcel model omits or consistently misrepresents processes and/or parameter(s) required to accurately simulate the droplet size distributions of the observed marine stratocumulus. By repeating our inverse methodology with more calibration parameters of which current measurements are uncertain (surface tension, mass accommodation coefficient), we find that it is likely that the process description within the current formulation of the pseudo-adiabatic cloud model used in this study misses a dynamical process rather than parameter(s).

  • 31. Rao, P. S. P.
    et al.
    Tiwari, Suresh
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Indian Institute of Tropical Meteorology, Pune, India.
    Matwale, J. L.
    Pervez, S.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Safai, P. D.
    Srivastava, A. K.
    Bisht, D. S.
    Singh, S.
    Hopke, P. K.
    Sources of chemical species in rainwater during monsoon and non-monsoonal periods over two mega cities in India and dominant source region of secondary aerosols2016In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 146, p. 90-99Article in journal (Refereed)
    Abstract [en]

    Samples of rainwater (RW) were collected to characterize the chemistry and sources in two representative megacities at Pune (Southwest) and Delhi (Northern) India from 2011 to 2014 across two seasons: monsoon (MN) and non-monsoon (NMN). Collected RW samples were analyzed for major chemical constituents (F-, Cl-, SO42-, NO3-, NH4+, Na+, K+, Ca2+, and Mg2+), pH and conductivity. In addition, bicarbonate (HCO3-) was also estimated. The mean pH values of the RW were >6 at Pune and <6 at Delhi and 4% and 26% were acidic, respectively. The mean sum of all measured ionic species in Pune and Delhi was 304.7 and 536.4 mu ep/l, respectively, indicating that significant atmospheric pollution effects in these Indian mega cities. Both the Ca2+ and SO42- were the dominant ions, accounting for 43% (Pune) and 54% (Delhi) of the total ions. The sum of measured ions during the NMN period was greater than the NM period by a factor of 1.5 for Pune (278.4: NM and 412.1: NMN mu eq/l) and a factor of about 2.5 for Delhi (406 and 1037.7 mu eq/l). The contributions of SO42- and NO3- to the RW acidity were similar to 40% and 60%, respectively, at Pune and correspondingly, 36% and 64% at Delhi. The concentrations of secondary aerosols (SO42- and NO3-) were higher by a factor of two and three when the air masses were transported to Pune from the continental side. At Delhi, the concentrations of SO42-, NO3-, Ca2+, and Mg2+ were significantly higher when the air masses arrive from Punjab, Haryana, and Pakistan indicating the greater atmospheric pollution over the Indo-Gangetic Plain. Positive matrix factorization was applied to the source apportionment of the deposition fluxes of these ions. Three factors were obtained for Pune and four for Delhi. The sources at Pune were secondary aerosols from fossil fuel combustion, soil dust, and marine, whereas, at Delhi, the sources were soil, fossil fuel combustion, biomass burning, and industrial chlorine.

  • 32.
    Rastak, Narges
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ekman, Annica
    Stockholm University, Faculty of Science, Department of Meteorology .
    Silvergren, S.
    Zieger, P.
    Wideqvist, U.
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Svenningsson, B.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Modeling Aerosol Water Uptake in The Arctic Based on The kappa-Kohler Theory2013In: Nucleation and Atmospheric Aerosols, American Institute of Physics (AIP), 2013, p. 702-705Conference paper (Refereed)
    Abstract [en]

    Water uptake or hygroscopicity is one of the most fundamental properties of atmospheric aerosols. Aerosol particles containing soluble materials can grow in size by absorbing water in ambient atmosphere. This property is measured by a parameter known as growth factor (GF), which is defined as the ratio of the wet diameter to the dry diameter. Hygroscopicity controls the size of an aerosol particle and therefore its optical properties in the atmosphere. Hygroscopic growth depends on the dry size of the particle, its chemical composition and the relative humidity in the ambient air (Fitzgerald, 1975; Pilinis et al., 1995). One of the typical problems in aerosol studies is the lack of measurements of aerosol size distributions and optical properties in ambient conditions. The gap between dry measurements and the real humid atmosphere is filled in this study by utilizing a hygroscopic model which calculates the hygroscopic growth of aerosol particles at Mt Zeppelin station, Ny Alesund, Svalbard during 2008.

  • 33.
    Rastak, Narges
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Silvergren, S.
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Wideqvist, Ulla
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Svenningsson, B.
    Maturilli, M.
    Tesche, Matthias
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Seasonal variation of aerosol water uptake and its impact on the direct radiative effect at Ny-Alesund, Svalbard2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 14, p. 7445-7460Article in journal (Refereed)
    Abstract [en]

    In this study we investigated the impact of water uptake by aerosol particles in ambient atmosphere on their optical properties and their direct radiative effect (ADRE, W m(-2)) in the Arctic at Ny-Alesund, Svalbard, during 2008. To achieve this, we combined three models, a hygroscopic growth model, a Mie model and a radiative transfer model, with an extensive set of observational data. We found that the seasonal variation of dry aerosol scattering coefficients showed minimum values during the summer season and the beginning of fall (July-August-September), when small particles (< 100 nm in diameter) dominate the aerosol number size distribution. The maximum scattering by dry particles was observed during the Arctic haze period (March-April-May) when the average size of the particles was larger. Considering the hygroscopic growth of aerosol particles in the ambient atmosphere had a significant impact on the aerosol scattering coefficients: the aerosol scattering coefficients were enhanced by on average a factor of 4.30 +/- 2.26 (mean +/- standard deviation), with lower values during the haze period (March-April-May) as compared to summer and fall. Hygroscopic growth of aerosol particles was found to cause 1.6 to 3.7 times more negative ADRE at the surface, with the smallest effect during the haze period (March-April-May) and the highest during late summer and beginning of fall (July-August-September).

  • 34. 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.

  • 35. Scott, C. E.
    et al.
    Rap, A.
    Spracklen, D. V.
    Forster, P. M.
    Carslaw, K. S.
    Mann, G. W.
    Pringle, K. J.
    Kivekas, N.
    Kulmala, M.
    Lihavainen, H.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    The direct and indirect radiative effects of biogenic secondary organic aerosol2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 1, p. 447-470Article in journal (Refereed)
    Abstract [en]

    We use a global aerosol microphysics model in combination with an offline radiative transfer model to quantify the radiative effect of biogenic secondary organic aerosol (SOA) in the present-day atmosphere. Through its role in particle growth and ageing, the presence of biogenic SOA increases the global annual mean concentration of cloud condensation nuclei (CCN; at 0.2% supersaturation) by 3.6-21.1 %, depending upon the yield of SOA production from biogenic volatile organic compounds (BVOCs), and the nature and treatment of concurrent primary carbonaceous emissions. This increase in CCN causes a rise in global annual mean cloud droplet number concentration (CDNC) of 1.9-5.2 %, and a global mean first aerosol indirect effect (AIE) of between +0.01 W m(-2) and -0.12 W m(-2). The radiative impact of biogenic SOA is far greater when biogenic oxidation products also contribute to the very early stages of new particle formation; using two organically mediated mechanisms for new particle formation, we simulate global annual mean first AIEs of -0.22 W m(-2) and -0.77 W m(-2). The inclusion of biogenic SOA substantially improves the simulated seasonal cycle in the concentration of CCN-sized particles observed at three forested sites. The best correlation is found when the organically mediated nucleation mechanisms are applied, suggesting that the first AIE of biogenic SOA could be as large as -0.77 W m(-2). The radiative impact of SOA is sensitive to the presence of anthropogenic emissions. Lower background aerosol concentrations simulated with anthropogenic emissions from 1750 give rise to a greater fractional CCN increase and a more substantial first AIE from biogenic SOA. Consequently, the anthropogenic indirect radiative forcing between 1750 and the present day is sensitive to assumptions about the amount and role of biogenic SOA. We also calculate an annual global mean direct radiative effect of between -0.08 W m(-2) and -0.78 W m(-2) in the present day, with uncertainty in the amount of SOA produced from the oxidation of BVOCs accounting for most of this range.

  • 36. Shinozuka, Y.
    et al.
    Clarke, A. D.
    Nenes, A.
    Jefferson, A.
    Wood, R.
    McNaughton, C. S.
    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).
    Redemann, J.
    Thornhill, K. L.
    Moore, R. H.
    Lathem, T. L.
    Lin, J. J.
    Yoon, Y. J.
    The relationship between cloud condensation nuclei (CCN) concentration and light extinction of dried particles: indications of underlying aerosol processes and implications for satellite-based CCN estimates2015In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 15, no 13, p. 7585-7604Article in journal (Refereed)
    Abstract [en]

    We examine the relationship between the number concentration of boundary-layer cloud condensation nuclei (CCN) and light extinction to investigate underlying aerosol processes and satellite-based CCN estimates. For a variety of airborne and ground-based observations not dominated by dust, regression identifies the CCN (cm(-3)) at 0.4 +/- 0.1% supersaturation with 10(0.3 alpha+1.3)sigma(0.75) where sigma (Mm(-1)) is the 500 nm extinction coefficient by dried particles and alpha is the Angstrom exponent. The deviation of 1 km horizontal average data from this approximation is typically within a factor of 2.0. partial derivative logCCN / partial derivative log sigma is less than unity because, among other explanations, growth processes generally make aerosols scatter more light without increasing their number. This, barring special meteorology-aerosol connections, associates a doubling of aerosol optical depth with less than a doubling of CCN, contrary to previous studies based on heavily averaged measurements or a satellite algorithm.

  • 37. Sinha, P. R.
    et al.
    Kondo, Y.
    Koike, M.
    Ogren, J. A.
    Jefferson, A.
    Barrett, T. E.
    Sheesley, R. J.
    Ohata, S.
    Moteki, N.
    Coe, H.
    Liu, D.
    Irwin, M.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Quinn, P. K.
    Zhao, Y.
    Evaluation of ground-based black carbon measurements by filter-based photometers at two Arctic sites2017In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 122, no 6, p. 3544-3572Article in journal (Refereed)
    Abstract [en]

    Long-term measurements of the light absorption coefficient (b(abs)) obtained with a particle soot absorption photometer (PSAP), b(abs) (PSAP), have been previously reported for Barrow, Alaska, and Ny-angstrom lesund, Spitsbergen, in the Arctic. However, the effects on b(abs) of other aerosol chemical species coexisting with black carbon (BC) have not been critically evaluated. Furthermore, different mass absorption cross section (MAC) values have been used to convert b(abs) to BC mass concentration (M-BC=b(abs)/MAC). We used a continuous soot monitoring system (COSMOS), which uses a heated inlet to remove volatile aerosol compounds, to measure b(abs) (b(abs) (COSMOS)) at these sites during 2012-2015. Field measurements and laboratory experiments have suggested that b(abs) (COSMOS) is affected by about 9% on average by sea-salt aerosols. M-BC values derived by COSMOS (M-BC (COSMOS)) using a MAC value obtained by our previous studies agreed to within 9% with elemental carbon concentrations at Barrow measured over 11months. b(abs) (PSAP) was higher than b(abs) (COSMOS), by 22% at Barrow (PM1) and by 43% at Ny-angstrom lesund (PM10), presumably due to the contribution of volatile aerosol species to b(abs) (PSAP). Using b(abs) (COSMOS) as a reference, we derived M-BC (PSAP) from b(abs) (PSAP) measured since 1998. We also established the seasonal variations of M-BC at these sites. Seasonally averaged M-BC (PSAP) decreased at a rate of about 0.550.30ngm(-3)yr(-1). We also compared M-BC (COSMOS) and scaled M-BC (PSAP) values with previously reported data and evaluated the degree of inconsistency in the previous data.

  • 38. Sporre, Moa K.
    et al.
    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).
    Swietlicki, Erik
    Kulmala, Markku
    Lihavainen, Heikki
    A study of the indirect aerosol effect on subarctic marine liquid low-level clouds using MODIS cloud data and ground-based aerosol measurements2012In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 116, p. 56-66Article in journal (Refereed)
    Abstract [en]

    Cloud microphysics is substantially affected by aerosol loading and the resulting changes in the reflective properties of the clouds can significantly affect the global radiation budget. A study of how marine low-level clouds over Barents Sea and the northern parts of the Norwegian Sea are affected by air mass origin has been performed by combining ground-based aerosol measurements with satellite cloud retrievals. Aerosol number size distributions have been obtained from measurement stations in northern Finland, and a trajectory model has been used to estimate the movement of the air masses. To identify anthropogenic influences on the clouds, the dataset has been divided according to aerosol loading. The clean air masses arrived to the investigation area from the north and the polluted air masses arrived from the south. Satellite derived microphysical and optical cloud parameters from the Moderate Resolution Imaging Spectrometer (MODIS) have then been analyzed for days when the trajectories coincided with marine low-level clouds over the investigated area. The cloud optical thickness (tau), cloud depth (H) and droplet number concentration (N-d) were significantly higher for the polluted days compared to the clean conditions, while the opposite was found for the cloud droplet effective radius (r(e)). The H and N-d were derived from the satellite retrievals of tau and r(e). Furthermore, calculations of the aerosol cloud interaction relationship (ACI), relating N-d to boundary layer aerosol concentrations, resulted in a value of 0.17, which is in line with previous remote sensing studies. The results demonstrate that ground-based aerosol measurements can be combined with satellite cloud observations to study the indirect aerosol effect, and that the microphysics of marine sub-polar clouds can be considerably affected by continental aerosols.

  • 39.
    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)
  • 40. 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.

  • 41.
    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.

  • 42.
    Tiwari, Suresh
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Indian Institute of Tropical Meteorology, India.
    Dumka, U. C.
    Hopke, P. K.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Srivastava, A. K.
    Bisht, D. S.
    Chakrabarty, R. K.
    Atmospheric heating due to black carbon aerosol during the summer monsoon period over Ballia: A rural environment over Indo-Gangetic Plain2016In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 178, p. 393-400Article in journal (Refereed)
    Abstract [en]

    Black carbon (BC) aerosols are one of the most uncertain drivers of global climate change. The prevailing view is that BC mass concentrations are low in rural areas where industrialization and vehicular emissions are at a minimum. As part of a national research program called the Ganga Basin Ground Based Experiment-2014 under the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) Phase-III of Ministry of Earth Sciences, Government of India, the continuous measurements of BC and particulate matter (PM) mass concentrations, were conducted in a rural environment in the highly-polluted Indo-Gangetic Plain region during 16th June to 15th August (monsoon period), 2014. The mean mass concentration of BC was 4.03 (+/- 0.85) mu g m(-3) with a daily variability between 2.4 and 5.64 mu g m(-3), however, the mean mass PM concentrations [near ultrafine (PM1.0), fine (PM2.5) and inhalable (PM1.0)] were 29.1(+/- 16.2), 34.7 (+/- 19.9) and 43.7 (+/- 283) mu g m(-3), respectively. The contribution of BC in PM1.0 was approximately 13%, which is one of the highest being recorded. Diurnally, the BC mass concentrations were highest (mean: 5.89 mu g m(-3)) between 20:00 to 22:00 local time (LT) due to the burning of biofuels/biomass such as wood, dung, straw and crop residue mixed with dung by the local residents for cooking purposes. The atmospheric direct radiative forcing values due to the composite and BC aerosols were determined to be +78.3, +44.9, and +45.0 W m(-2) and +42.2, +35.4 and +34.3 W m(-2) during the months ofJune, July and August, respectively. The corresponding atmospheric heating rates (AHR) for composite and BC aerosols were 2.21,1.26 and 1.26; and 1.19, 0.99 and 0.96 K day(-1) for the month ofJune, July and August, respectively, with a mean of 1.57 and 1.05 K day(-1) which was 33% lower AHR (BC) than for the composite particles during the study period. This high AHR underscores the importance of absorbing aerosols such as BC contributed by residential cooking using biofuels in India. Our study demonstrates the need for immediate, effective regulations and policies that mitigate the emission of BC particles from domestic cooking in rural areas of India.

  • 43.
    Tiwari, Suresh
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Indian Institute of Tropical Meteorology, New Delhi Branch, India.
    Kumar, R.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Singh, S.
    Panicker, A. S.
    Significant cooling effect on the surface due to soot particles over Brahmaputra River Valley region, India: An impact on regional climate2016In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 562, p. 504-516Article in journal (Refereed)
    Abstract [en]

    Black carbon (BC) is an important atmospheric aerosol constituent that affects the climate by absorbing (directly) the sunlight and modifying cloud characteristics (indirectly). Here, we present first time yearlong measurements of BC and carbon monoxide (CO) from an urban location of Guwahati located in the Brahmaputra River valley (BRV) in the northeast region of India from 1st July 2013 to 30th June 2014. Daily BC concentrations varied within the range of 2.86 to 11.56 mu g m(-3) with an annual average of 7.17 +/- 1.89 mu g m(-3), while, CO varied from 0.19 to 1.20 ppm with a mean value of 0.51 +/- 0.19 ppm during the study period. The concentrations of BC (8.37 mu g m(-3)) and CO (0.67 ppm) were similar to 39% and similar to 55% higher during the dry months (October to March) than the wet months (April to September) suggesting that seasonal changes in meteorology and emission sources play an important role in controlling these species. The seasonal Delta BC/Delta CO ratios were highest (lowest) in the pre-monsoon (winter) 18.1 +/- 1.4 mu g m(-3) ppmv(-1) (12.6 +/- 2.2 mu g m(-3) ppmv(-1)) which indicate the combustion of biofuel/biomass as well as direct emissions from fossil fuel during the pre-monsoon season. The annual BC emission was estimated to be 2.72 Gg in and around Guwahati which is about 44% lower than the mega city 'Delhi' (4.86 Gg). During the study period, the annual mean radiative forcing (RF) at the top of the atmosphere (TOA) for clear skies of BC was +9.5Wm(-2), however, the RF value at the surface (SFC) was -21.1 Wm(-2) which indicates the net warming and cooling effects, respectively. The highest RF at SFC was in the month of April (-30 Wm(-2)) which is coincident with the highest BC mass level. The BC atmospheric radiative forcing (ARF) was +30.16 (annualmean) Wm(-2) varying from +23.1 to +43.8 Wm(-2). The annualmean atmospheric heating rate (AHR) due to the BC aerosols was 0.86 K day(-1) indicates the enhancement in radiation effect over the study region. The Weather Research and Forecasting model coupled with Chemistry(WRF-Chem) captured the seasonal cycle of observed BC fairly well but underestimated the observed BC during the month of May-August. Model results show that BC at Guwahati is controlled mainly by anthropogenic emissions except during the pre-monsoon season when open biomass burning also makes a similar contribution.

  • 44.
    Tiwari, Suresh
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Indian Institute of Tropical Meteorology, India.
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Hopke, Philip K.
    Srivastava, A. K.
    Bisht, D. S.
    Pandey, A. K.
    Observations of ambient trace gas and PM10 concentrations at Patna, Central Ganga Basin during 2013-2014: The influence of meteorological variables on atmospheric pollutants2016In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 180, p. 138-149Article in journal (Refereed)
    Abstract [en]

    Atmospheric pollutants including ozone (O-3), sulfur dioxide (SO2), oxides of nitrogen (NOx), carbon monoxide (CO), and inhalable particulate matter (PM10) were measured in the central Indo-Gangetic Basin (IGB) at Patna, India, from 1st March 2013 to 31st December 2014, and significant variability was observed in the temporal patterns of these pollutant concentrations. The mean O-3, SO2, NO, NO2, CO (trace gases: TG), and PM10 (PM) concentrations were 14.5 +/- 4.8, 5.9 +/- 4.8, 23.1 +/- 22, 20.6 +/- 14.6 ppb, 1.5 +/- 0.7 ppm, and 192.0 +/- 132.8 ng/m(3), respectively, over the study period. The highest concentrations of these species were during the post-monsoon and winter seasons except O-3 and SO2 that showed the highest concentrations during the pre-monsoon. The lowest concentrations of TG and PM were observed during the monsoon season as a result of scavenging by rain. NO and NO2 along with PM concentrations decreased by similar to 76,19, and 63% when the wind speed (WS) was >0.5 m/s. However, for O-3, an opposite trend was observed with similar to 14% higher concentrations. The WS was negatively correlated with PM during the winter (-0.48) and post-monsoon (-0.32) seasons. In order to investigate the source region of TG and PM, 5-day air mass back trajectories were computed. The dominance of the air masses (92, 53, and 49%) were from the IGB is highly polluted during the winter, pre-monsoon, and post-monsoon, respectively. The TG and PM were observed much higher during these periods. During the biomass burning period (post-monsoon), the trajectory analysis showed that the TG and PM concentrations were around three-fold higher (flow from the IGB) than the other seasons. To improve air quality over IGB, the mitigation measures should be designed to reduce emissions from both local and regional sources.

  • 45. Treffeisen, Renatte
    et al.
    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).
    Herber, Andreas
    Bareiss, J
    Helbig, A
    Stone, RS
    Hoyningen-Huene, W
    Krejci, Radovan
    Department of Meteorology.
    Stohl, Andreas
    Neuber, Roland
    Arctic smoke – aerosol characteristics during a record air pollution event in the European Arctic and its radiative impact2007In: Atmospheric Chemistry and Physics, Vol. 7, p. 3035-3053Article in journal (Refereed)
  • 46.
    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)
  • 47.
    Tunved, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Korhonen, Hannele
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Lehtinen, Kari
    Kulmala, Markku
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    A pseudo-Lagrangian model study of the size distribution properties over Scandinavia: Transport from Aspvreten to Värriö2004In: Atmospheric Chemistry and Physics Discussions, ISSN 1680-7367, no 4, p. 7757-7794Article in journal (Refereed)
    Abstract [en]

    The evolution of the aerosol size distribution during transport between Aspvreten (58.8° N, 17.4° E) and Värriö (67.46° N, 29.35° E) was studied using a pseudo-Lagrangian approach. Aerosol dynamic processes were studied and interpreted utilizing a state-of-the-art aerosol dynamic box model UHMA (University of Helsinki Multicomponent Aerosol model) complemented with OH, NO3, O3 and terpene chemistry. In the model simulations, the growth and formation of aerosol particles was controlled by sulphuric acid, ammonia, water and an unidentified low volatile organic compound. This organic compound was assumed to be a product of terpene oxidation with a yield of 13% in the base case conditions. Changes of aerosol size distribution properties during transport between the stations were examined in twelve clear sky cases. On average, the modelled number agreed fairly well with observations. Mass concentration was overestimated by 10%. Apart from dilution, the only removal mechanism for aerosol mass is dry deposition. A series of sensitivity tests performed revealed that the absolute magnitude of dry deposition effects on the aerosol size distribution is slow overall. Furthermore, nucleation does not leave a significant contribution to aerosol number in the selected cases. The sensitivity of the modelled size distribution to concentration of precursor gases and oxidants is, however, obvious. In order to explain observed mass increase during transport we conclude that a yield of low volatile products from oxidation of terpenes of 10–15% is required to explain observed growth rates. Coagulation is acknowledged to be highly important in modelled cases.

  • 48.
    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

  • 49.
    Tunved, Peter
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Partridge, David G.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Korhonen, H.
    New trajectory-driven aerosol and chemical process model Chemical and Aerosol Lagrangian Model (CALM)2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 21, p. 10161-10185Article in journal (Refereed)
    Abstract [en]

    A new Chemical and Aerosol Lagrangian Model (CALM) has been developed and tested. The model incorporates all central aerosol dynamical processes, from nucleation, condensation, coagulation and deposition to cloud formation and in-cloud processing. The model is tested and evaluated against observations performed at the SMEAR II station located at Hyytiala (61 degrees 51'N, 24 degrees 17'E) over a time period of two years, 2000-2001. The model shows good agreement with measurements throughout most of the year, but fails in reproducing the aerosol properties during the winter season, resulting in poor agreement between model and measurements especially during December-January. Nevertheless, through the rest of the year both trends and magnitude of modal concentrations show good agreement with observation, as do the monthly average size distribution properties. The model is also shown to capture individual nucleation events to a certain degree. This indicates that nucleation largely is controlled by the availability of nucleating material (as prescribed by the [H2SO4]), availability of condensing material (in this model 15% of primary reactions of monoterpenes (MT) are assumed to produce low volatile species) and the properties of the size distribution (more specifically, the condensation sink). This is further demonstrated by the fact that the model captures the annual trend in nuclei mode concentration. The model is also used, alongside sensitivity tests, to examine which processes dominate the aerosol size distribution physical properties. It is shown, in agreement with previous studies, that nucleation governs the number concentration during transport from clean areas. It is also shown that primary number emissions almost exclusively govern the CN concentration when air from Central Europe is advected north over Scandinavia. We also show that biogenic emissions have a large influence on the amount of potential CCN observed over the boreal region, as shown by the agreement between observations and modeled results for the receptor SMEAR II, Hyytiala, during the studied period.

  • 50.
    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

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