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  • 1.
    Aamaas, Borgar
    et al.
    Ctr Int Climate & Environm Res Oslo, N-0318 Oslo, Norway.;Univ Oslo, UiO, N-0316 Oslo, Norway.;UNIS, Univ Ctr Svalbard, N-9171 Longyearbyen, Norway..
    Boggild, Carl Egede
    UNIS, Univ Ctr Svalbard, N-9171 Longyearbyen, Norway..
    Stordal, Frode
    Univ Oslo, UiO, N-0316 Oslo, Norway..
    Berntsen, Terje
    Ctr Int Climate & Environm Res Oslo, N-0318 Oslo, Norway.;Univ Oslo, UiO, N-0316 Oslo, Norway..
    Holmen, Kim
    UNIS, Univ Ctr Svalbard, N-9171 Longyearbyen, Norway.;Polar Environm Ctr, NPI, N-9296 Tromso, Norway..
    Ström, Johan
    Stockholm Univ, S-10691 Stockholm, Sweden.;Polar Environm Ctr, NPI, N-9296 Tromso, Norway..
    Elemental carbon deposition to Svalbard snow from Norwegian settlements and long-range transport2011Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 63, nr 3, s. 340-351Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact on snow pack albedo from local elemental carbon (EC) sources in Svalbard has been investigated for the winter of 2008. Highly elevated EC concentrations in the snow are observed around the settlements of Longyearbyen and Svea (locally > 1000 ng g(-1), about 200 times over the background level), while EC concentrations similar to the background level are seen around Ny-Alesund. Near Longyearbyen and Svea, darkened snow influenced by wind transported coal dust from open coal stockpiles is clearly visible from satellite images and by eye at the ground. As a first estimate, the reduction in snow albedo caused by local EC pollution from the Norwegian settlements has been compared to the estimated reduction caused by long-range transported EC for entire Svalbard. The effect of local EC from Longyearbyen, Svea and all Norwegian settlements are estimated to 2.1%, 7.9% and 10% of the total impact of EC, respectively. The EC particles tend to stay on the surface during melting, and elevated EC concentrations due to the spring melt was observed. This accumulation of EC enhances the positive albedo feedbacks. The EC concentrations were observed to be larger in metamorphosed snow than in fresh snow, and especially around ice lenses.

  • 2.
    Behrenfeldt, Ulrika
    et al.
    Stockholm Univ, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    Krejci, Radovan
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Ström, Johan
    Stockholm Univ, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    Stohl, Andreas
    NILU, Norwegian Inst Air Res, Kjeller, Norway..
    Chemical properties of Arctic aerosol particles collected at the Zeppelin station during the aerosol transition period in May and June of 20042008Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 60, nr 3, s. 405-415Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Single particle analysis was performed on samples taken at the Zeppelin Station, Svalbard, during the ASTAR campaign, 2004. Thirteen samples were selected to representatively cover the campaign period and different weather conditions. This particular period also covers the transition from an accumulation mode dominated size distribution in spring to an Aitken mode dominated aerosol size distribution in summer. Altogether, 1353 particles were analysed and their elemental composition documented. Another 1225 were counted but not characterized chemically. The samples were compared with respect to chemical composition, aerosol size, shape and airmass origin. The comparison showed that the samples taken before the aerosol size transition were dominated by spherical 'organic like' particles in the submicrometre range, with an Eurasian influence. The samples taken after the size transition showed a more complex character and the source origin was the Arctic basin. In this period, an increase of both marine aerosol groups as well as groups of continental origin became more pronounced. This apparent contradiction may have its explanation in cloud scavenging processes, removing the hygroscopic particles from the old continental air, leaving the more hydrophobic particles, at the same time, as the ocean source will provide a more maritime character.

  • 3. Bigg, E K
    et al.
    Leck, C
    Nilsson, E D
    Sudden changes in arctic atmospheric aerosol concentrations during summer and autumn1996Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 48, nr 2, s. 254-271Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The International Arctic Ocean Expedition of 1991 measured number concentrations of condensation nuclei and cloud condensation nuclei from 1 August to 6 October between latitudes 70 degrees N and 90 degrees N. Changes in concentration of more than a factor of 2 in 1 h or less were frequent in spite of the long distances from significant sources and often appeared in groups separated by times of the order of 1 h. These observations provide a unique opportunity to study interacting meteorological mechanisms in the stable marine boundary layer. It is suggested that most of these changes were due to two Factors: (1) large vertical concentration gradients caused mainly by interaction of aerosol and clouds and (2) intermittent localised mixing into the shallow surface mixed layer, caused by atmospheric wave motions or roll vortices. Quasi-periodic changes of smaller amplitude were present for about 35% of the total time with mean periods in the range 60-90 min. About 1/6 of the sudden large changes, usually involving an isolated decrease and recovery in accumulation mode particle number concentrations, is attributed to mixing caused by shear-induced Kelvin-Helmholtz breaking waves. Regular sequences of maxima and minima were about as common but involved 2/3 of all such changes because of the number of events in each sequence. Satellite images, radiosonde wind profiles and the typical mean periods suggested that roll vortices were common in the high Arctic. The associated mixing changes seemed to account adequately for the alternating maxima and minima in aerosol number concentrations. The special conditions of atmospheric stability and high Frequencies of low cloud cover in the high Arctic combined with the absence of strong local sources of particles have allowed us to identify processes of mixing that often drastically modified aerosol size distributions and concentrations near the surface which are likely to have a far more general application. These Factors have to be added to studies of chemical and physical processes influencing the life cycle of the aerosol and air transport, in order to understand the sources, sinks and to define the radiative forcing by the atmospheric aerosol in the Arctic and elsewhere.

  • 4.
    Björkman, Mats P.
    et al.
    Fram Ctr, Norwegian Polar Inst, N-9296 Tromso, Norway.;Univ Oslo, Dept Geosci, N-0316 Oslo, Norway..
    Kuhnel, Rafael
    Fram Ctr, Norwegian Polar Inst, N-9296 Tromso, Norway.;Univ Oslo, Dept Geosci, N-0316 Oslo, Norway..
    Partridge, Daniel G.
    Stockholm Univ, Dept Appl Environm Sci, SE-11418 Stockholm, Sweden.;Univ Oxford, Dept Phys, Oxford OX1 3PU, England..
    Roberts, Tjarda J.
    Fram Ctr, Norwegian Polar Inst, N-9296 Tromso, Norway.;Univ Orleans, CNRS, LPC2E, UMR 7328, F-45071 Orleans 2, France..
    Aas, Wenche
    NILU Norwegian Inst Air Res, Inst 18, N-2027 Kjeller, Norway..
    Mazzola, Mauro
    CNR, Inst Atmospher Sci & Climate ISAC CNR, I-40129 Bologna, Italy..
    Viola, Angelo
    CNR, Inst Atmospher Sci & Climate ISAC CNR, I-00133 Rome, Italy..
    Hodson, Andy
    Univ Sheffield, Dept Geog, Sheffield S10 2TN, S Yorkshire, England..
    Ström, Johan
    Stockholm Univ, Dept Appl Environm Sci, SE-11418 Stockholm, Sweden..
    Isaksson, Elisabeth
    Fram Ctr, Norwegian Polar Inst, N-9296 Tromso, Norway..
    Nitrate dry deposition in Svalbard2013Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, artikel-id 19071Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Arctic regions are generally nutrient limited, receiving an extensive part of their bio-available nitrogen from the deposition of atmospheric reactive nitrogen. Reactive nitrogen oxides, as nitric acid (HNO3) and nitrate aerosols (p-NO3), can either be washed out from the atmosphere by precipitation or dry deposited, dissolving to nitrate (NO3-). During winter, NO3- is accumulated in the snowpack and released as a pulse during spring melt. Quantification of NO3- deposition is essential to assess impacts on Arctic terrestrial ecology and for ice core interpretations. However, the individual importance of wet and dry deposition is poorly quantified in the high Arctic regions where in-situ measurements are demanding. In this study, three different methods are employed to quantify NO3- dry deposition around the atmospheric and ecosystem monitoring site, Ny-Alesund, Svalbard, for the winter season (September 2009 to May 2010): (1) A snow tray sampling approach indicates a dry deposition of -10.27 +/- 3.84 mg m(-2) (+/- S.E.); (2) A glacial sampling approach yielded somewhat higher values -30.68 +/- 12.00 mg m(-2); and (3) Dry deposition was also modelled for HNO3 and p-NO3 using atmospheric concentrations and stability observations, resulting in a total combined nitrate dry deposition of -10.76 +/- 1.26 mg m(-2). The model indicates that deposition primarily occurs via HNO3 with only a minor contribution by p-NO3. Modelled median deposition velocities largely explain this difference: 0.63 cm s(-1) for HNO3 while p-NO3 was 0.0025 and 0.16 cm s(-1) for particle sizes 0.7 and 7 mm, respectively. Overall, the three methods are within two standard errors agreement, attributing an average 14% (total range of 2-44%) of the total nitrate deposition to dry deposition. Dry deposition events were identified in association with elevated atmospheric concentrations, corroborating recent studies that identified episodes of rapid pollution transport and deposition to the Arctic.

  • 5.
    Bäckstrand, Kristina
    et al.
    Stockholms universitet, Institutionen för geologi och geokemi.
    Crill, Patrick, M.
    Stockholms universitet, Institutionen för geologi och geokemi.
    Mastepanov, Mikhail
    Stockholms universitet, Institutionen för geologi och geokemi.
    Christensen, Torben, R.
    INES, University of Lund.
    Bastviken, David
    Stockholms universitet, Institutionen för geologi och geokemi.
    Nonmethane volatile organic compound flux from a subarctic mire in northern Sweden2008Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 60, nr 2, s. 226-237Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Biogenic NMVOCs are mainly formed by plants and microorganisms. They have strong impact on the local atmospheric chemistry when emitted to the atmosphere. The objective of this study was to determine if there are significant emissions of non-methane volatile organic compounds (NMVOCs) from a subarctic mire in northern Sweden. Subarctic peatlands in discontinuous permafrost regions are undergoing substantial environmental changes due to their high sensitivity to climate warming and there is need for includingNMVOCs in the overall carbon budget. Automatic and manual chamber measurements were used to estimateNMVOCfluxes from three dominating subhabitats on the mire during three growing seasons. Emission rates varied and were related to plant species distribution and seasonal net ecosystem exchange of carbon dioxide. The highest fluxes were observed from wetter sites dominated by Eriophorum and Sphagnum spp. Total NMVOC emissions from the mire (∼17 ha) is estimated to consist of ∼150 kgC during a growing season with 150 d. NMVOC fluxes can account for ∼5% of total net carbon exchange (−3177 kgC) at the mire during the same period. NMVOC emissions are therefore a significant component in a local carbon budget for peatlands

  • 6. Covert, D S
    et al.
    Wiedensohler, A
    Aalto, P
    Heintzenberg, J
    McMurry, P H
    Leck, C
    Aerosol number size distributions from 3 to 500 nm diameter in the arctic marine boundary layer during summer and autumn1996Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 48, nr 2, s. 197-212Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aerosol physics measurements made onboard the Swedish icebreaker Oden in the late Summer and early Autumn of 1991 during the International Arctic Ocean Expedition (IAOE-91) have provided the first data on the size distribution of particles in the Arctic marine boundary layer (MEL) that cover both the number and mass modes of the size range from 3 to 500 nm diameter. These measurements were made in conjunction with atmospheric gas and condensed phase chemistry measurements in an effort to understand a part of the ocean-atmosphere sulfur cycle. Analysis of the particle physics data showed that there were three distinct number modes in the submicrometric aerosol in the Arctic MEL. These modes had geometric mean diameters of around 170 nm, 45 nm and 14 nm referred to as accumulation, Aitken and ultrafine modes, respectively. There were clear minima in number concentrations between the modes that appeared at 20 to 30 nm and at 80 to 100 nm. The total number concentration was most frequently between 30 and 60 particles cm(-3) with a mean value of around 100 particles cm(-3), but the hourly average concentration varied over two to three orders of magnitude during the 70 days of the expedition. On average, the highest concentration was in the accumulation mode that contained about 45% of the total number, while the Aitken mode contained about 40%. The greatest variability was in the ultrafine mode concentration which is indicative of active, nearby sources (nucleation from the gas phase) and sinks; the Aitken and accumulation mode concentrations were much less variable. The ultrafine mode was observed about two thirds of the time and was dominant 10% of the time. A detailed description and statistical analysis of the modal aerosol parameters is presented here.

  • 7.
    Engvall, Ann-Christine
    et al.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Krejci, Radovan
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Ström, Johan
    Univ Stockholm, Atmospher Sci Unit, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    Minikin, Andreas
    Deutsches Zentrum Luft & Raumfahrt DLR, Inst Atmospher Phys, D-82234 Oberpfaffenhofen, Wessling, Germany..
    Treffeisen, Renate
    Alfred Wegener Inst Polar & Marine Res, D-14473 Potsdam, Germany..
    Stohl, Andreas
    Norwegian Inst Air Res, N-2027 Kjeller, Norway..
    Herber, Andreas
    Alfred Wegener Inst Polar & Marine Res, D-27570 Bremerhaven, Germany..
    In-situ airborne observations of the microphysical properties of the Arctic tropospheric aerosol during late spring and summer2008Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 60, nr 3, s. 392-404Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In-situ aerosol data collected in the Arctic troposphere during a three-week period in 2004 were analysed. The measurements took place during late spring, i.e., at the time of the year when the characteristics of the aerosol distribution change from being accumulation-mode dominated to being primarily of the Aitken-mode type, a process that previously has been observed in the boundary layer. To address the question whether this transition is also detectable in the free troposphere of an aircraft-measured data from the ASTAR 2004 campaign were analysed. In this study, we present vertically as well as temporally results from both ground-based and airborne measurements of the total number concentrations of particles larger than 10 and 260 nm. Aircraft-measured size distributions of the aerosol ranging from 20 to 2200 nm have been evaluated with regard to conditions in the boundary layer as well as in the free troposphere. Furthermore an analysis of the volatile fraction of the aerosol population has been performed both for the integrated and size-distributed results. From these investigations we find that the transition takes place in the entire troposphere.

  • 8.
    Engvall, Ann-Christine
    et al.
    Norwegian Inst Air Res NILU, N-2027 Kjeller, Norway..
    Ström, Johan
    Norwegian Polar Res Inst, N-9296 Tromso, Norway..
    Tunved, Peter
    Stockholm Univ, Dept Appl Environm Sci, Atmospher Sci Unit, S-10691 Stockholm, Sweden..
    Krejci, Radovan
    Stockholm Univ, Dept Appl Environm Sci, Atmospher Sci Unit, S-10691 Stockholm, Sweden..
    Schlager, Hans
    Inst Phys & Atmosphare, Deutsch Zentrum Luft & Raumfahrt, D-82234 Oberpfaffenhofen, Wessling, Germany..
    Minikin, Andreas
    Inst Phys & Atmosphare, Deutsch Zentrum Luft & Raumfahrt, D-82234 Oberpfaffenhofen, Wessling, Germany..
    The radiative effect of an aged, internally mixed Arctic aerosol originating from lower-latitude biomass burning2009Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 61, nr 4, s. 677-684Artikel i tidskrift (Refereegranskat)
    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.

  • 9.
    Hegg, Dean A.
    et al.
    Univ Washington, Dept Atmospher Sci, Seattle, WA 98195 USA..
    Clarke, Antony D.
    Univ Hawaii, Sch Ocean & Earth Sci & Technol, Honolulu, HI 96822 USA..
    Doherty, Sarah J.
    Univ Washington, JISAO, Seattle, WA 98195 USA..
    Ström, Johan
    Norwegian Polar Res Inst, Tromso, Norway.;Stockholm Univ, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    Measurements of black carbon aerosol washout ratio on Svalbard2011Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 63, nr 5, s. 891-900Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Simultaneous measurements of aerosol black carbon (BC) in both fresh snow and in air on Svalbard are presented. From these, washout ratios for BC are calculated and compared to sparse previous measurements of this metric in the arctic. The current ratios are significantly higher than previously found measured values. We argue that the degree of snow riming within the accretion zone can explain most of this difference. Using an analytical model of the scavenging process, BC scavenging efficiencies are estimated to lie in the range 0.25-0.5, comparable to measured values.

  • 10. HEINTZENBERG, J
    et al.
    LECK, C
    SEASONAL-VARIATION OF THE ATMOSPHERIC AEROSOL NEAR THE TOP OF THE MARINE BOUNDARY-LAYER OVER SPITSBERGEN RELATED TO THE ARCTIC SULFUR CYCLE1994Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 46, nr 1, s. 52-67Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With an emphasis on marine biogenic sulphur the first 26 months of fine particle, (< 1 mum radius), aerosol data from the new air chemistry station on Zeppelinfjellet, Spitsbergen, (79-degrees-N, 12-degrees-E, 474 m asl), were evaluated to elucidate source- and transformation processes of the Arctic aerosol. Results from 2 particle counters, an integrating nephelometer, and filter samples were available for our interpretation. On the filters we had analysed soot, (EC), sodium, (Na+), methansulphonate, MSA-, and sulphate, (SO42-). Fine particle composition revealed a strong regional marine biological source of MSA- and SO42- which we estimated to contribute 26% to the non-sea salt sulphur in summer. In winter, no more than 2% of the non-sea-salt sulphur could be attributed to the marine biological source. Rigorous air mass analyses combined with the EC data as a tracer for regional anthropogenic combustion sources showed that this regional biological source became active already in March over the Barents Sea and over the North Atlantic. In summer, the levels of the biogenic sulphur components were very similar to those measured at the southern hemispheric marine site of Cape Grim, (1.5 and 0.92 nmol m-3 for MSA- and nss-SO42-, respectively). For samples with minimum anthropogenic influence we found a constant MSA-/nss-SO42- ratio in the fine particle size range. This ratio had a value of 28% and was temperature-independent. Our results comprise the first long-term record of Arctic aerosol data taken in the upper part of the planetary boundary layer which often is influenced by persistent Arctic stratus. With a cloud-segregation scheme we segregated the aerosol data into a group measured interstitially, i.e., inside boundary layer clouds, (INT), and an out-of cloud group, (OOC). Average INT/OOC-ratios of fine particle mass, nss-SO42-, and soot were 0.19, 0.21 and 0.21, respectively. While exhibiting similar INT/OOC-ratioS in winter, MSA- had an average INT/OOC-ratio of 0.63 in summer implying that it was less scavenged than the other components. Complementary physical aerosol data corroborated our interpretation of MSA- on average residing on smaller particles than nss-SO42-. Together with the scavenging results our data support the concept that MSA- most likely is formed by condensation onto existing particles while SO42- predominantly is formed by in-cloud oxidation of SO2.

  • 11. Heintzenberg, J
    et al.
    Leck, C
    Birmili, W
    Wehner, B
    Tjernstrom, M
    Wiedensohler, A
    Aerosol number-size distributions during clear and fog periods in the summer high Arctic: 1991, 1996 and 20012006Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 58, nr 1, s. 41-50Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present study covers submicrometer aerosol size distribution data taken during three Arctic icebreaker expeditions in the summers of 1991 1996 and 2001. The size distributions of all expeditions were compared in log-normally fitted form to the statistics of the marine number size distribution provided by Heintzenberg et al. (2004) yielding rather similar log-normal parameters of the modes. Statistics of the modal concentrations revealed strong concentration decreases of large accumulation mode particles with increasing length of time spent over the pack ice. The travel-time dependencies of both Aitken and ultrafine modes strongly indicate, its other studies did before, the occurrence of fine-particle Sources in the inner Arctic. With two approaches evidence of fog-related aerosol source processes was sought for in the data sets of 1996 and 2001 because they included fog drop size distributions. With increasing fog intensity modes in interstitial particle number concentrations appeared in particular in the size range around 80 run that was nearly mode free in clear air. A second, dynamic approach revealed that Aitken mode concentrations increased strongly above their respective fog-period medians in both years before maximum drop numbers were reached in both years. We interpret the results of both approaches as strong indications of fog-related aerosol source processes as discussed in Leek and Bigg (1999) that need to be elucidated with further data from dedicated fog experiments in future Arctic expeditions in order to understand the life cycle of the aerosol over the high Arctic pack ice area.

  • 12.
    Jonsson, Anders
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Åberg, Jan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Jansson, Mats
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Variations in pCO2 during summer in the surface water of an unproductive lake in northern Sweden2007Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 59, nr 5, s. 797-803Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Unproductive lakes are generally supersaturated with carbon dioxide (CO2) and emit CO2 to the atmosphere continuously during ice-free periods. However, temporal variation of the partial pressure of CO2 (pCO2) and thus of CO2 evasion to atmosphere is poorly documented. We therefore carried out temporally high-resolution (every 6 h) measurements of the pCO2 using an automated logger system in the surface water of a subarctic, unproductive, lake in the birch forest belt. The study period was June–September 2004. We found that the pCO2 showed large seasonal variation, but low daily variation. The seasonal variation was likely mainly caused by variations in input and mineralization of allochthonous organic matter. Stratification depth probably also influenced pCO2 of the surface water by controlling the volume in which mineralization of dissolved organic carbon (DOC) occurred. In lakes, with large variations in pCO2, as in our study lake a high (weekly) sampling intensity is recommended for obtaining accurate estimates of the evasion of CO2.

  • 13. Karl, Matthias
    et al.
    Gross, Allan
    Pirjola, Liisa
    Leck, Caroline
    A new flexible multicomponent model for the study of aerosol dynamics in the marine boundary layer2011Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 63, nr 5, s. 1001-1025Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new sectional aerosol dynamics model, MAFOR, was developed with the focus to study nucleation in the marine boundary layer. Novel aspects of the model are (1) flexibility in the treatment of gas phase chemistry, (2) treatment of liquid phase chemistry, which can be extended according to needs and (3) simultaneous calculation of number and mass concentration distributions of a multicomponent aerosol as functions of time. Comparison with well-documented aerosol models (MONO32 and AEROFOR), a comprehensive data set on gas phase compounds, aerosol size distribution and chemical composition obtained during the AOE-96 (Arctic Ocean Expedition, 1996) was used to evaluate the model. Dimethyl sulphide decay during advection of an air parcel over the Arctic pack ice was well captured by the applied models and predicted concentrations of gaseous sulphuric acid and methane sulphonic acid range up to 1.0 x 10(6) cm(-3) and 1.8 x 10(6) cm(-3), respectively. Different nucleation schemes were implemented in MAFOR which allow the simulation of new particle formation. Modelled nucleation rates from sulphuric acid nucleation via cluster activation were up to 0.21 cm(-3) s(-1) while those from ion-mediated nucleation were below 10(-2) cm(-3) s(-1). Classical homogeneous binary and ternary nucleation theories failed to predict nucleation over the central Arctic Ocean in summer.

  • 14. Karl, Matthias
    et al.
    Leck, Caroline
    Gross, Allan
    Pirjola, Liisa
    A study of new particle formation in the marine boundary layer over the central Arctic Ocean using a flexible multicomponent aerosol dynamic model2012Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 64Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Enhancement of number concentrations of particles with sizes less than 25 nm diameter has been frequently observed in the boundary layer over the central Arctic Ocean during summer. The sectional aerosol dynamics model for Marine Aerosol Formation (MAFOR) was applied to evaluate the capability of different nucleation mechanisms to reproduce nucleation events observed during three expeditions (1996, 2001 and 2008) onboard the Swedish icebreaker Oden. Model calculations suggest that a source rate of a condensable organic vapour (OV) of about 2 x 10(5) cm(-3) s(-1) is required to reproduce observed growth of nucleation mode particles. Nucleation rates predicted by the newly proposed combined sulphuric acid nucleation mechanism, which best described new particle formation in the Arctic, ranged from 0.04 to 0.1 cm(-3) s(-1). This mechanism additively combines ion-mediated nucleation and cluster activation, and treats condensation of OV without correction of the Kelvin effect. In several events, the simultaneous number enhancement of particles in the 20-50 nm size range remained unexplained by the nucleation mechanisms. This lends support to alternative theories such as the fragmentation of marine gels (approximate to 200-500 nm diameter in size) by physical or chemical processes.

  • 15. Leck, C
    et al.
    Bigg, E K
    Biogenic particles in the surface microlayer and overlaying atmosphere in the central Arctic Ocean during summer2005Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 57, nr 4, s. 305-316Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transmission electron microscopy photographs of airborne particles are compared with those of particles found in the surface microlayer of the open water between ice floes in the central Arctic Ocean in summer. The similarity in morphology, physical properties, X-ray spectra and a chemical reaction of the numerous aggregates and their building blocks predominantly smaller than 70 nm diameter, and of bacteria and other micro-organisms found in both, strongly suggests that the airborne particles were ejected from the water by bursting bubbles. The shape of the size distribution of aggregates in the air is very similar to that in the water, each with a well-defined Aitken mode but shifted towards smaller sizes. Diffuse electron-transparent material joining and surrounding the heat resistant and non-hygroscopic particulates in both the air and water is shown to have properties consistent with the exopolymer secretions (EPS) of microalgae and bacteria in the water. EPS are highly surface-active, highly hydrated molecules that can spontaneously assemble into gels. They are broken down by ultraviolet light or acidification. These properties provide an explanation for the different resistance to dehydration of bacteria from air and water samples when subjected to a vacuum, and the apparent absence of sea salt on airborne bacteria and aggregates. The difference in size distribution between the air and water samples is also explained. The role of EPS and particulate matter from the open lead surface microlayer in the production of the airborne Aitken mode particles and cloud condensation nuclei is examined and concluded to be very important.

  • 16. Leck, C
    et al.
    Bigg, E K
    Covert, D S
    Heintzenberg, J
    Maenhaut, W
    Nilsson, E D
    Wiedensohler, A
    Overview of the atmospheric research program during the international arctic ocean expedition of 1991 (IAOE-91) and its scientific results1996Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 48, nr 2, s. 136-155Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The broad aim of the Atmospheric program of the International Arctic Ocean Expedition (IAOE-91) was to test the hypothesis that marine biogenically produced dimethyl sulfide (DMS) gas can exert a significant global climatic control. The hypothesis states that DMS is transferred to the atmosphere and is oxidised to form airborne particles. Some of these grow large enough to act as cloud condensation nuclei (CCN) which help determine cloud droplet concentration. The latter has a strong influence on cloud albedo and hence on the radiation balance of the area affected. In summer, the central Arctic is a specially favourable region for studying the natural sulfur cycle in that the open waters surrounding the pack ice are the only significant sources of DMS and there are almost no anthropogenic particle sources. Concentrations of seawater and atmospheric DMS decreased at about the same rate during the period of measurements, (1 August to 6 October, latitudes 75 degrees N to 90 degrees N) spanning about three orders of magnitude. Methane sulfonate and non-sea salt sulfate in the submicrometer particles, which may be derived from atmospheric DMS, also decreased similarly, suggesting that the first part of the hypothesis under test was true. Influences on cloud droplet concentration and radiation balance could not be measured. Size-resolved aerosol chemistry showed a much lower proportion of methane sulfonate to be associated with supermicrometer particles than has been found elsewhere. Its molar ratio to non-sea salt sulfate suggested that the processes controlling the particulate chemistry do not exhibit a net temperature dependence. Elemental analysis of the aerosol also revealed the interesting possibility that debris from Siberian rivers transported on the moving ice represent a fairly widespread source of supermicrometer crustal material within the pack ice. Highly resolved measurements of aerosol number size distributions were made in the diameter range 3 nm to 500 nm. 3 distinct modal sizes were usually present, the ‘’ultrafine”, ‘’Aitken” and ‘’accumulation” modes centred on 14, 45 and 170 nm diameter, respectively. The presence of ultrafine particles, implying recent production, was more frequent than has been found in lower latitude remote marine areas. Evidence suggests that they were mixed to the surface from higher levels. Sudden and often drastic changes in aerosol concentration and size distribution were surprisingly frequent in view of the relatively slowly changing meteorology of the central Arctic during the study period and the absence of strong pollution sources. They were most common in particles likely to have taken part in cloud formation (> 80 nm diameter). 2 Factors appear to have been involved in these sudden changes. The Ist was the formation of vertical gradients in aerosol concentration due to interactions between particles and clouds or favoured regions for new particle production during periods of stability. The 2nd was sporadic localised breakdowns of the stability, bringing changed particle concentrations to the measurement level. Probable reasons for these sporadic mixing events were indicated by the structure of the Marine Boundary Layer (MEL) investigated with high resolution rawinsondes. Low level jets were present about 60% of the time, producing conditions conductive to turbulence and shear-induced waves. It is concluded that an even more detailed study of meteorological processes in the MBL in conjunction with more highly time-resolved measurements of gas-aerosol physics and chemistry appears to be essential in any future research aimed at studying the indirect, cloud mediated, effect of aerosol particles.

  • 17. Leck, C
    et al.
    Heintzenberg, J
    Engardt, M
    A meridional profile of the chemical composition of submicrometre particles over the East Atlantic Ocean: regional and hemispheric variabilities2002Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 54, nr 4, s. 377-394Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Within the framework of SWEDARP (Swedish Antarctic Program) 92,93 an aerosol sampling program was carried out on board of M/S Palarbjorn which carried staff and material to the Nordic Antarctic Field exercises during the Austral summer 1992/1993. The cruise started 11 November 1992 from Oslo, went via Cape Town to Antarctica, and then back to Cape Town ,here the ship arrived on 4 January 1993. During the cruise, a meridional profile of physical and chemical submicrometre aerosol properties was derived covering the East Atlantic Ocean from 60degreesN to 70degreesS. The multicomponent aerosol data set combined with a trajectory analysis revealed a systematic meridional distribution of aerosol sources over the Atlantic that covered European and African continental Plumes and, South of 15degreesS, a largely biologically controlled marine aerosol. Median number concentrations calculated over the whole cruise spanned a factor of 20 between 2000 and 100 cm(-3), while total analyzed mass concentrations ranged between 7800 and 40 ng m(3). From the biologically dominated subset of the data in the southern hemisphere, relationships were developed that allowed an apportionment of the observed sulfate and ammonium concentration to biogenic and anthropogenic Sources over the whole meridional aerosol profile.

  • 18. Leck, C
    et al.
    Persson, C
    Seasonal and short-term variability in dimethyl sulfide, sulfur dioxide and biogenic sulfur and sea salt aerosol particles in the arctic marine boundary layer during summer and autumn1996Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 48, nr 2, s. 272-299Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The International Arctic Ocean Expedition (IAOE), lasting from August to mid-October 1991, provided a unique opportunity to characterise and quantify relationships within the natural sulfur cycle in the marine boundary layer under conditions of limited anthropogenic influence. Concentrations of dimethyl sulfide, sulfur dioxide, and submicrometer aerosol concentrations of methane sulfonate, non-sea-salt sulfate, ammonium and elemental carbon ranged from 17 to 0.05 nmol m(-3) (380 to 1 ppt(v)), 1.7 to 0.04 nmol m(-3) (38 to 0.9 ppt(v)), 1.4 to 0.002 nmol m(-3) (31 to 0.05 ppt(v)), 6.9 to 0.03 nmol m(-3) (155 to 0.7 ppt(v)), 3.9 to 0.03 nmol m(-3) (90 to 0.7 ppt(v)) and 0.51 to 0.009 nmol m(-3) (11 to 0.2 ppt(v)), respectively. Observations showed a seasonal variation of concentrations with highest values for all the marine biogenic sulfur gas-aerosol parametres along the ice edge zone in August and lowest values over the pack ice in late September. On average concentrations fell with a decline rate of about 20-40% per week. A similar seasonal change was also reflected in particulate ammonium. This therefore indicates links between the different sulfur compounds as well as between the biogenic sulfur and nitrogen cycles. Concentrations over the pack ice region were generally lower than over the open waters at the ice edge with an estimated net loss rate of roughly 35% per day of transport over the pack ice. Contrary to earlier marine sulfur studies performed outside the Arctic region, a constant methane sulfonate to non-sea-salt sulfate molar ratio was found in the submicrometer size fraction for samples with a minimal influence from fog and anthropogenic sources. This ratio had a value of 0.22 in spite of large seasonal changes in temperature and concentrations of methane sulfonate and non-sea-salt sulfate. Thus we conclude that the sum of the processes controlling the measured particle properties do not exhibit a net temperature dependence. The one to one molar ratio of ammonium to non-sea-salt sulfate indicated a partly neutralised ammoniated sulfate aerosol. This was further verified by single particle analysis. Measurements of non-sea-salt sulfate and ammonium revealed a bimodal size distribution with about 70% of their mass found in the submicrometer size fraction. Methane sulfonate was mainly associated with submicrometer particles, with less than 8% of the mass observed in the largest particles. We have also shown that the interchange of air between the surface mixed layer and clouds, caused by atmospheric wave motions, dominated the short time variations in atmospheric DMS and submicrometer aerosol concentrations. This interchange will have a strong influence on the chemical and physical processes that control the properties of the aerosol, and deserves more attention in future work.

  • 19. Leck, C
    et al.
    Persson, C
    The central Arctic Ocean as a source of dimethyl sulfide - Seasonal variability in relation to biological activity1996Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 48, nr 2, s. 156-177Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Seawater dimethyl sulfide (DMS) and distribution of phytoplankton biomass were investigated in relation to sea ice conditions, hydrography and nutrients, onboard the Swedish icebreaker Oden as a part of the International Arctic Ocean Expedition, 1991. The expedition lasted from the beginning of August until the middle of October and covered sampling between 75 to 90 degrees N in the open waters and along the ice edge zone in the Greenland Sea-Fram Strait area as well as in the pack ice of the western part of the Nansen and Amundsen basins and in the Makarov basin. Surface seawater DMS concentrations showed a clear seasonal progression related to biological activity, ranging from 0.04 to 12 nmol dm(-3). The highest values were found in open waters along the ice edge in the beginning of August, while the lowest concentrations were measured beneath heavy pack ice in late September. On average DMS Fell about 30 % per week in the open waters south of and within the ice edge zone whereas a significant higher seasonal decline, about 45 % per week, was observed in the pack ice during freeze-up. The importance of the phytoplankton bloom and zooplankton abundance both at the ice edge zone and in the pack ice during summer ice-melt to DMS concentrations in seawater has been demonstrated. We also demonstrated a potential for intense DMS production in the open waters in the wake of the receding ice. The extremely low surface concentrations of DMS during the freeze-up of the pack ice were probably primarily controlled by removal processes within the water column. The turnover time of DMS in the pack ice water column was calculated to be of the order of 13 days with the most effective sink seemingly of micro-biological origin. Although, our limited set of data indicated the likelyhood of a relationship between DMS and degraded phytoplankton material (phaeopigments), seawater DMS showed no simple correlation with phytoplankton standing stock over the large areas and different seasons covered. The area weighed summer and winter fluxes of DMS from the Arctic Polar Ocean to the atmosphere were estimated to be 2.0 and 0.03 mu mol m(-2) day(-1), respectively. On an annual basis, winter biogenic sulfur emissions are negligible compared to the summer emissions in the region. The total emissions of marine biogenic sulfur from the Northern Hemispheric high latitudes was estimated to be approximately 4 Gmol yr(-1).

  • 20. Leck, Caroline
    et al.
    Bigg, E. Keith
    Comparison of sources and nature of the tropical aerosol with the summer high Arctic aerosol2008Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 60, nr 1, s. 118-126Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Marine aerosol was collected in September 1998 and July 2005 on the upwind coast of an island at latitude 15 degrees S, about 15 km downwind from the outer edge of the Great Barrier Reef, Australia, and examined by electron microscopy. Exopolymer gels, aggregates of organic particles, marine micro-organisms and fragments of marine life formed a substantial part of the accumulation mode aerosol. Differences in transparency, firmness of outlines and shape of gels and the influence of organic vapours on them, suggested progressive physical and chemical changes with atmospheric residence time. The organic aggregate components had a size distribution remarkably close to that found in similar particles over the central Arctic Ocean peaking at diameters of 30-40 nm. Single components or small groups of these aggregates were found within at least 75% of particles resembling ammonium sulphate in appearance, indicating that aggregates fragmented in the atmosphere. Sea salt was not detected in particles < 200 nm diameter unlike many observations showing it to be a major component, a result that was entirely consistent with the Arctic findings. The deduced sequence of changes to particles entering the atmosphere from the ocean is also very similar to that found in the Arctic, suggesting that it is a common pattern over the oceans. That conclusion would require modification of the parametrization of the marine aerosol used in climate models and of possible climate feedback effects.

  • 21. Li, Xin
    et al.
    Hede, Thomas
    Tu, Yaoquan
    Leck, Caroline
    Agren, Hans
    Cloud droplet activation mechanisms of amino acid aerosol particles: insight from molecular dynamics simulations2013Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Atmospheric amino acids constitute a large fraction of water-soluble organic nitrogen compounds in aerosol particles, and have been confirmed as effective cloud condensation nuclei (CCN) materials in laboratory experiments. We present a molecular dynamics (MD) study of six amino acids with different structures and chemical properties that are relevant to the remote marine atmospheric aerosol-cloud system, with the aim of investigating the detailed mechanism of their induced changes in surface activity and surface tension, which are important properties for cloud drop activation. Distributions and orientations of the amino acid molecules are studied; these L-amino acids are serine (SER), glycine (GLY), alanine (ALA), valine (VAL), methionine (MET) and phenylalanine (PHE) and are categorised as hydrophilic and amphiphilic according to their affinities to water. The results suggest that the presence of surface-concentrated amphiphilic amino acid molecules give rise to enhanced Lennard-Jones repulsion, which in turn results in decreased surface tension of a planar interface and an increased surface tension of the spherical interface of droplets with diameters below 10 nm. The observed surface tension perturbation for the different amino acids under study not only serves as benchmark for future studies of more complex systems, but also shows that amphiphilic amino acids are surface active. The MD simulations used in this study reproduce experimental results of surface tension measurements for planar interfaces and the method is therefore applicable for spherical interfaces of nano-size for which experimental measurements are not possible to conduct.

  • 22. Lohmann, U
    et al.
    Leck, C
    Importance of submicron surface-active organic aerosols for pristine Arctic clouds2005Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 57, nr 3, s. 261-268Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent results from summer measurement campaigns over the partly ice covered central Arctic Ocean show that the high Arctic aerosol has a larger organic fraction than previously thought. We use a Lagrangian parcel model to infer the properties of the unexplained organic aerosol fraction that is necessary for reproducing the observed concentrations of cloud condensation nuclei (CCN). With increasing distance from the open ocean a highly surface-active Aitken mode, associated with particles found in the open lead surface microlayer, becomes increasingly important for cloud droplet formation. The presence of such an Aitken mode population increases the high Arctic indirect aerosol effect (added cooling) relative to just a marine source of CCN from oxidation products of dimethyl sulfide (DMS) released from phytoplankton.

  • 23.
    Lunden, Jenny
    et al.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Svensson, Gunilla
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Wisthaler, Armin
    Univ Innsbruck, Inst Ionenphys & Angew Phys, A-6020 Innsbruck, Austria..
    Tjernström, Michael
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Hansel, Armin
    Univ Innsbruck, Inst Ionenphys & Angew Phys, A-6020 Innsbruck, Austria..
    Leck, Caroline
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    The vertical distribution of atmospheric DMS in the high Arctic summer2010Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 62, nr 3, s. 160-171Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The vertical structure of gas-phase dimethyl sulphide [DMS(g)] in the high Arctic atmosphere is investigated during a summer season. The model results show that the near-surface DMS(g) concentration over open ocean is very variable both in time and space, depending on the local atmospheric conditions. Profiles over ocean have typically highest concentration near the surface and decrease exponentially with height. Over the pack-ice, the concentrations are typically lower and the vertical structure changes as the air is advected northward. Modelled DMS(g) maxima above the local boundary layer were present in about 3% of the profiles found over the pack-ice. These maxima were found in association to frontal zones. Our results also show that DMS(g) can be mixed downward by turbulence into the local boundary layer and act as a local near-surface DIMS(g) source over the pack-ice and may hence influence the growth of cloud condensation nuclei and cloud formation in the boundary layer. Profile observations are presented in support to the model results. They show that significant DMS(g) concentrations exist in the Arctic atmosphere at altitudes not to be expected when only considering vertical mixing in the boundary layer.

  • 24. Maenhaut, W
    et al.
    Ducastel, G
    Leck, C
    Nilsson, E D
    Heintzenberg, J
    Multi-elemental composition and sources of the high Arctic atmospheric aerosol during summer and autumn1996Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 48, nr 2, s. 300-321Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During the International Arctic Ocean Expedition 1991 (IAOE-91), total (i.e., < 10 mu m equivalent aerodynamic diameter (EAD)) and size-fractionated aerosol samples were collected using single filters, slacked filters and cascade impactors. The samples were analyzed for the particulate mass (PM) and up to about 50 particulate species and elements by gravimetry, instrumental multi-elemental analysis techniques and ion chromatography. The results from parallel samples, taken with the different devices and analyzed by independent techniques, were intercompared. In the samples collected over open waters (ocean subset), the median total ( < 10 mu m EAD) concentrations of non-sea-salt S (nss-S) and Na were 124 and 490 ng/m(3), respectively, but these medians were reduced to 25 and 20 ng/m(3) in the samples collected in the pack ice covered high Arctic (pack ice subset). For the mineral dust elements and anthropogenic metals, however, the levels tended to be higher in the pack ice subset than in the ocean subset. Overall, very low concentrations were observed for PM and the various particulate species in the pack ice subset, but the levels were quite similar to those obtained for background samples from the Ymer-80 expedition. With the exception of elemental carbon, S and I, all species and elements measured, including the typical anthropogenic metals (e.g., Zn, As, and Sb), were predominantly associated with the coarse ( > 2 mu m EAD) size fraction. The highest levels of the anthropogenic metals and of the mineral dust elements were found in air which in general had not been in contact with large continental or anthropogenic source regions during the last 5 or even 10 days prior to its arrival, and in an area of the pack ice which was influenced by continental river run-of from the Siberian coast. It is tentatively suggested that the elevated concentrations of both those metals and the crustal elements were the result of local mechanical windblown generation of coarse aerosols from the river effluent materials which were present on or at the surface of the ice. By relating the observed atmospheric nss-S levels to 3-dimensional air back trajectories, and from intercomparing the nss-S time trend with the trends of various other particulate species, it was concluded that the nss-S was mainly from anthropogenic origin (transported through the free troposphere) near the end of the IAOE-91, but that the marine biogenic sulfur source must have dominated during the first month and a half of the expedition.

  • 25. Nilsson, E D
    et al.
    Leck, C
    A pseudo-Lagrangian study of the sulfur budget in the remote Arctic marine boundary layer2002Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 54, nr 3, s. 213-230Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The atmospheric Sulfur cycle of the remote Arctic marine boundary layer is studied using trajectories and measurements Of Sulfur Compounds from the International Arctic Ocean Expedition 1991, along with a pseudo-Lagrangian approach and in analytical model. The dimethyl sulfide [DMS(g)] turnover time was 59(-9)(+18) h. Only 25(-9)(+11%) of DMS(g) followed reaction paths to sulfur dioxide [SO2(g)], Sub-micrometre aerosol non-seasalt sulfate (nss-SO42-) or methane sulfonate (MSA). During the first 3 d of transport over the pack ice, fog deposition and drizzle resulted in short turnover times: 16(-6)(+8) h for SO2(g), 18(-4)(+4) for MSA and 18(-3)(+2) h for nss-SO42-. Therefore, DMS(g) will, owing to its origin along or south of the ice edge and longer turnover time, survive the original sub-micrometre Sulfur aerosol mass and gradually replace it with new biogenic Sulfur aerosol mass. The advection of DMS(g) along with heal and moisture will influence the Clouds and fogs over the Arctic pack ice through the formation Of Cloud condensation nuclei (CCN). If the pack ice cover were to decrease owing to a climate change, the total Arctic Ocean DMS production would change, and potentially there Could be an ice-DMS-cloud-albedo climate feedback effect, but it would be accompanied by changes in the fog aerosol sink.

  • 26.
    Ström, Johan
    et al.
    Stockholm Univ, Dept Appl Environm Sci, S-10691 Stockholm, Sweden.;Norwegian Polar Res Inst, N-9296 Tromso, Norway..
    Engvall, Ann-Christine
    Norwegian Inst Air Res, NILU, N-2027 Kjeller, Norway..
    Delbart, Frank
    IPEV French Polar Inst, CNRS, F-29280 Plouzane, France..
    Krejci, Radovan
    Norwegian Inst Air Res, NILU, N-2027 Kjeller, Norway..
    Treffeisen, Renate
    Alfred Wegener Inst, D-14473 Potsdam, Germany..
    On small particles in the Arctic summer boundary layer: observations at two different heights near Ny-Alesund, Svalbard2009Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 61, nr 2, s. 473-482Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 27. SVENNINGSSON, BIRGITTA
    et al.
    ARNETH, ALMUT
    HAYWARD, SEAN
    HOLST, THOMAS
    MASSLING, ANDREAS
    SWIETLICKI, ERIK
    HIRSIKKO, ANNE
    JUNNINEN, HEIKKI
    RIIPINEN, ILONA
    VANA, MARKO
    MASO, MIIKKA DAL
    HUSSEIN, TAREQ
    KULMALA, MARKKU
    Aerosol particle formation events and analysis of high growth rates observed above a subarctic wetland–forest mosaic2008Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 60, nr 3, s. 353-364Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An analysis of particle formation (PF) events over a subarctic mire in northern Sweden was performed, based on number–size distributions of atmospheric aerosol particles (10–500 nm in diameter) and ions (0.4–40 nm in Tammet diameter). We present classification statistics for PF events from measurements covering the period July 2005–September 2006, with a break over the winter period. The PF event frequency peaked during the summer months, in contrast to other Scandinavian sites where the frequency is highest during spring and autumn. Our analysis includes calculated growth rates and estimates of concentrations and production rates of condensing vapour, deduced from the growth rates and condensational sink calculations, using AIS and SMPS data. Particle formation events with high growth rates (up to 50 nm h−1) occurred repeatedly. In these cases, the newly formed nucleation mode particles were often only present for periods of a few hours. On several occasions, repeated particle formation events were observed within 1 d, with differences in onset time of a few hours. These high growth rates were only observed when the condensation sink was higher than 0.001 s−1.

  • 28. Wiedensohler, A
    et al.
    Covert, D S
    Swietlicki, E
    Aalto, P
    Heintzenberg, J
    Leck, C
    Occurrence of an ultrafine particle mode less than 20 nm in diameter in the marine boundary layer during Arctic summer and autumn1996Ingår i: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 48, nr 2, s. 213-222Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The International Arctic Ocean Expedition 1991 (IAOE-91) provided a platform to study the occurrence and size distributions of ultrafine particles in the marine boundary layer (MEL) during Arctic summer and autumn. Measurements of both aerosol physics, and gas/particulate chemistry were taken aboard the Swedish icebreaker Oden. Three separate submicron aerosol modes were found: an ultrafine mode (D-p < 20 nm), the Aitken mode (20 < D-p < 100 nm), and the accumulation mode (D-p > 100 nm). We evaluated correlations between ultrafine particle number concentrations and mean diameter with the entire measured physical, chemical, and meteorological data set. Multivariate statistical methods were then used to make these comparisons. A principal component (PC) analysis indicated that the observed variation in the data could be explained by the influence from several types of air masses. These were characterised by contributions from the open sea or sources from the surrounding continents and islands. A partial least square (PLS) regression of the ultrafine particle concentration was also used. These results implied that the ultrafine particles were produced above or in upper layers of the MBL and mixed downwards. There were also indications that the open sea acted as a source of the precursors for ultrafine particle production. No anti-correlation was found between the ultrafine and accumulation particle number concentrations, thus indicating that the sources were in separate air masses.

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