Change search
Refine search result
1 - 41 of 41
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Abbatt, J. P. D.
    et al.
    Thomas, J. L.
    Abrahamsson, K.
    Boxe, C.
    Granfors, A.
    Jones, A. E.
    King, M. D.
    Saiz-Lopez, A.
    Shepson, P. B.
    Sodeau, J.
    Toohey, D. W.
    Toubin, C.
    von Glasow, R.
    Wren, S. N.
    Yang, X.
    Halogen activation via interactions with environmental ice and snow in the polar lower troposphere and other regions2012In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, no 14, p. 6237-6271Article in journal (Refereed)
    Abstract [en]

    The role of ice in the formation of chemically active halogens in the environment requires a full understanding because of its role in atmospheric chemistry, including controlling the regional atmospheric oxidizing capacity in specific situations. In particular, ice and snow are important for facilitating multiphase oxidative chemistry and as media upon which marine algae live. This paper reviews the nature of environmental ice substrates that participate in halogen chemistry, describes the reactions that occur on such substrates, presents the field evidence for ice-mediated halogen activation, summarizes our best understanding of ice-halogen activation mechanisms, and describes the current state of modeling these processes at different scales. Given the rapid pace of developments in the field, this paper largely addresses advances made in the past five years, with emphasis given to the polar boundary layer. The integrative nature of this field is highlighted in the presentation of work from the molecular to the regional scale, with a focus on understanding fundamental processes. This is essential for developing realistic parameterizations and descriptions of these processes for inclusion in larger scale models that are used to determine their regional and global impacts.

  • 2.
    Birch, C. E.
    et al.
    Univ Leeds, Inst Climate & Atmospher Sci, Leeds, W Yorkshire, England..
    Brooks, I. M.
    Univ Leeds, Inst Climate & Atmospher Sci, Leeds, W Yorkshire, England..
    Tjernström, M.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Shupe, M. D.
    Univ Colorado, Boulder, CO 80309 USA.;NOAA ESRL, Boulder, CO USA..
    Mauritsen, T.
    Max Planck Inst Meteorol, Hamburg, Germany..
    Sedlar, J.
    Swedish Meteorol & Hydrol Inst, S-60176 Norrkoping, Sweden..
    Lock, A. P.
    Met Off, Exeter, Devon, England..
    Earnshaw, P.
    Met Off, Exeter, Devon, England..
    Persson, P. O. G.
    Univ Colorado, Boulder, CO 80309 USA.;NOAA ESRL, Boulder, CO USA..
    Milton, S. F.
    Met Off, Exeter, Devon, England..
    Leck, C.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Modelling atmospheric structure, cloud and their response to CCN in the central Arctic: ASCOS case studies2012In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, no 7, p. 3419-3435Article in journal (Refereed)
    Abstract [en]

    Observations made during late summer in the central Arctic Ocean, as part of the Arctic Summer Cloud Ocean Study (ASCOS), are used to evaluate cloud and vertical temperature structure in the Met Office Unified Model (MetUM). The observation period can be split into 5 regimes; the first two regimes had a large number of frontal systems, which were associated with deep cloud. During the remainder of the campaign a layer of low-level cloud occurred, typical of central Arctic summer conditions, along with two periods of greatly reduced cloud cover. The short-range operational NWP forecasts could not accurately reproduce the observed variations in near-surface temperature. A major source of this error was found to be the temperature-dependant surface albedo parameterisation scheme. The model reproduced the low-level cloud layer, though it was too thin, too shallow, and in a boundary-layer that was too frequently well-mixed. The model was also unable to reproduce the observed periods of reduced cloud cover, which were associated with very low cloud condensation nuclei (CCN) concentrations (< 1 cm(-3)). As with most global NWP models, the MetUM does not have a prognostic aerosol/cloud scheme but uses a constant CCN concentration of 100 cm(-3) over all marine environments. It is therefore unable to represent the low CCN number concentrations and the rapid variations in concentration frequently observed in the central Arctic during late summer. Experiments with a single-column model configuration of the MetUM show that reducing model CCN number concentrations to observed values reduces the amount of cloud, increases the near-surface stability, and improves the representation of both the surface radiation fluxes and the surface temperature. The model is shown to be sensitive to CCN only when number concentrations are less than 10-20 cm(-3).

  • 3. Browse, J.
    et al.
    Carslaw, K. S.
    Mann, G. W.
    Birch, C. E.
    Arnold, S. R.
    Leck, C.
    The complex response of Arctic aerosol to sea-ice retreat2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 14, p. 7543-7557Article in journal (Refereed)
  • 4. Chang, R. Y. -W
    et al.
    Leck, C.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Graus, M.
    Univ Innsbruck, Inst Ion Phys & Appl Phys, A-6020 Innsbruck, Austria..
    Müeller, M.
    Univ Innsbruck, Inst Ion Phys & Appl Phys, A-6020 Innsbruck, Austria..
    Paatero, J.
    Finnish Meteorol Inst, FIN-00101 Helsinki, Finland..
    Burkhart, J. F.
    Norwegian Inst Air Res NILU, Kjeller, Norway.;Univ Calif, Sierra Nevada Res Inst, Merced, CA USA..
    Stohl, A.
    Norwegian Inst Air Res NILU, Kjeller, Norway..
    Orr, L. H.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Hayden, K.
    Environm Canada, Sci & Technol Branch, Downsview, ON, Canada..
    Li, S. -M
    Hansel, A.
    Univ Innsbruck, Inst Ion Phys & Appl Phys, A-6020 Innsbruck, Austria..
    Tjernström, M.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Leaitch, W. R.
    Environm Canada, Sci & Technol Branch, Downsview, ON, Canada..
    Abbatt, J. P. D.
    Univ Toronto, Dept Chem, Toronto, ON M5S 1A1, Canada..
    Aerosol composition and sources in the central Arctic Ocean during ASCOS2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 20, p. 10619-10636Article in journal (Refereed)
    Abstract [en]

    Measurements of submicron aerosol chemical composition were made over the central Arctic Ocean from 5 August to 8 September 2008 as a part of the Arctic Summer Cloud Ocean Study (ASCOS) using an aerosol mass spectrometer (AMS). The median levels of sulphate and organics for the entire study were 0.051 and 0.055 mu gm(-3), respectively. Positive matrix factorisation was performed on the entire mass spectral time series and this enabled marine biogenic and continental sources of particles to be separated. These factors accounted for 33% and 36% of the sampled ambient aerosol mass, respectively, and they were both predominantly composed of sulphate, with 47% of the sulphate apportioned to marine biogenic sources and 48% to continental sources, by mass. Within the marine biogenic factor, the ratio of methane sulphonate to sulphate was 0.25+/-0.02, consistent with values reported in the literature. The organic component of the continental factor was more oxidised than that of the marine biogenic factor, suggesting that it had a longer photochemical lifetime than the organics in the marine biogenic factor. The remaining ambient aerosol mass was apportioned to an organic-rich factor that could have arisen from a combination of marine and continental sources. In particular, given that the factor does not correlate with common tracers of continental influence, we cannot rule out that the organic factor arises from a primary marine source.

  • 5.
    de Boer, G.
    et al.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Earth Syst Res Lab, Div Phys Sci, Boulder, CO USA..
    Shupe, M. D.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Earth Syst Res Lab, Div Phys Sci, Boulder, CO USA..
    Caldwell, P. M.
    Lawrence Livermore Natl Lab, Livermore, CA USA..
    Bauer, S. E.
    Columbia Univ, Earth Inst, New York, NY USA.;NASA, Goddard Inst Space Studies, New York, NY 10025 USA..
    Persson, O.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Earth Syst Res Lab, Div Phys Sci, Boulder, CO USA..
    Boyle, J. S.
    Lawrence Livermore Natl Lab, Livermore, CA USA..
    Kelley, M.
    NASA, Goddard Inst Space Studies, New York, NY 10025 USA..
    Klein, S. A.
    Lawrence Livermore Natl Lab, Livermore, CA USA..
    Tjernström, M.
    Univ Stockholm, Dept Meteorol, S-10691 Stockholm, Sweden..
    Near-surface meteorology during the Arctic Summer Cloud Ocean Study (ASCOS): evaluation of reanalyses and global climate models2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 1, p. 427-445Article in journal (Refereed)
    Abstract [en]

    Atmospheric measurements from the Arctic Summer Cloud Ocean Study (ASCOS) are used to evaluate the performance of three atmospheric reanalyses (European Centre for Medium Range Weather Forecasting (ECMWF)-Interim reanalysis, National Center for Environmental Prediction (NCEP)-National Center for Atmospheric Research (NCAR) reanalysis, and NCEP-DOE (Department of Energy) reanalysis) and two global climate models (CAM5 (Community Atmosphere Model 5) and NASA GISS (Goddard Institute for Space Studies) ModelE2) in simulation of the high Arctic environment. Quantities analyzed include near surface meteorological variables such as temperature, pressure, humidity and winds, surface-based estimates of cloud and precipitation properties, the surface energy budget, and lower atmospheric temperature structure. In general, the models perform well in simulating large-scale dynamical quantities such as pressure and winds. Near-surface temperature and lower atmospheric stability, along with surface energy budget terms, are not as well represented due largely to errors in simulation of cloud occurrence, phase and altitude. Additionally, a development version of CAMS, which features improved handling of cloud macro physics, has demonstrated to improve simulation of cloud properties and liquid water amount. The ASCOS period additionally provides an excellent example of the benefits gained by evaluating individual budget terms, rather than simply evaluating the net end product, with large compensating errors between individual surface energy budget terms that result in the best net energy budget.

  • 6. Engvall, A. -C
    et al.
    Krejci, R.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Ström, J.
    Stockholm Univ, Dept Appl Environm Sci, Atmospher Sci Unit, S-10691 Stockholm, Sweden.;Norwegian Polar Res Inst, N-9296 Tromso, Norway..
    Treffeisen, R.
    Alfred Wegener Inst Polar & Marine Res, D-14473 Potsdam, Germany..
    Scheele, R.
    Koninklijk Nederlands Meteorol Inst, NL-3730 AE De Bilt, Netherlands..
    Hermansen, O.
    Norsk Inst Luftforskning, N-2027 Kjeller, Norway..
    Paatero, J.
    Finnish Meteorol Inst, FIN-00101 Helsinki, Finland..
    Changes in aerosol properties during spring-summer period in the Arctic troposphere2008In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 8, no 3, p. 445-462Article in journal (Refereed)
    Abstract [en]

    The change in aerosol properties during the transition from the more polluted spring to the clean summer in the Arctic troposphere was studied. A six-year data set of observations from Ny-Aalesund on Svalbard, covering the months April through June, serve as the basis for the characterisation of this time period. In addition four-day-back trajectories were used to describe air mass histories. The observed transition in aerosol properties from an accumulation-mode dominated distribution to an Aitken-mode dominated distribution is discussed with respect to long-range transport and influences from natural and anthropogenic sources of aerosols and pertinent trace gases. Our study shows that the air-mass transport is an important factor modulating the physical and chemical properties observed. However, the air-mass transport cannot alone explain the annually repeated systematic and rather rapid change in aerosol properties, occurring within a limited time window of approximately 10 days. With a simplified phenomenological model, which delivers the nucleation potential for new-particle formation, we suggest that the rapid shift in aerosol microphysical properties between the Arctic spring and summer is mainly driven by the incoming solar radiation in concert with transport of precursor gases and changes in condensational sink.

  • 7.
    Hansen, A. M. K.
    et al.
    Aarhus Univ, Dept Chem, DK-8000 Aarhus, Denmark.;Aarhus Univ, iNANO, DK-8000 Aarhus, Denmark..
    Kristensen, K.
    Aarhus Univ, Dept Chem, DK-8000 Aarhus, Denmark.;Aarhus Univ, iNANO, DK-8000 Aarhus, Denmark..
    Nguyen, Q. T.
    Aarhus Univ, Dept Chem, DK-8000 Aarhus, Denmark.;Aarhus Univ, iNANO, DK-8000 Aarhus, Denmark.;Aarhus Univ, Dept Environm Sci, Roskilde, Denmark..
    Zare, A.
    Aarhus Univ, Dept Chem, DK-8000 Aarhus, Denmark.;Aarhus Univ, iNANO, DK-8000 Aarhus, Denmark.;Aarhus Univ, Dept Environm Sci, Roskilde, Denmark.;Univ Tehran, Inst Geophys, Tehran, Iran..
    Cozzi, F.
    Aarhus Univ, Dept Chem, DK-8000 Aarhus, Denmark.;Aarhus Univ, iNANO, DK-8000 Aarhus, Denmark..
    Nojgaard, J. K.
    Aarhus Univ, Dept Environm Sci, Roskilde, Denmark..
    Skov, H.
    Aarhus Univ, Dept Environm Sci, Roskilde, Denmark.;Univ Southern Denmark, Inst Chem Engn & Biotechnol & Environm Technol, Odense, Denmark..
    Brandt, J.
    Aarhus Univ, Dept Environm Sci, Roskilde, Denmark..
    Christensen, J. H.
    Aarhus Univ, Dept Environm Sci, Roskilde, Denmark..
    Ström, J.
    Stockholm Univ, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    Tunved, P.
    Stockholm Univ, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    Krejci, R.
    Stockholm Univ, Dept Appl Environm Sci, S-10691 Stockholm, Sweden.;Univ Helsinki, Dept Phys, Helsinki, Finland..
    Glasius, M.
    Aarhus Univ, Dept Chem, DK-8000 Aarhus, Denmark.;Aarhus Univ, iNANO, DK-8000 Aarhus, Denmark..
    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.

  • 8. Heintzenberg, J.
    et al.
    Leck, C.
    The summer aerosol in the central Arctic 1991–2008: did it change or not?2012In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, no 9, p. 3969-3983Article in journal (Refereed)
    Abstract [en]

    In the course of global warming dramatic changes are taking place in the Arctic and boreal environments. However, physical aerosol data in from the central summer Arctic taken over the course of 18 yr from 1991 to 2008 do not show systematic year-to-year changes, albeit substantial interannual variations. Besides the limited extent of the data several causes may be responsible for these findings. The processes controlling concentrations and particle size distribution of the aerosol over the central Arctic perennial pack ice area, north of 80°, may not have changed substantially during this time. Environmental changes are still mainly effective in the marginal ice zone, the ice-free waters and continental rims and have not propagated significantly into the central Arctic yet where they could affect the local aerosol and its sources. The analysis of meteorological conditions of the four expedition summers reveal substantial variations which we see as main causes of the measured variations in aerosol parameters. With combined lognormal fits of the hourly number size distributions of the four expeditions representative mode parameters for the summer aerosol in the central Arctic have been calculated. The combined aerosol statistics discussed in the present paper provide comprehensive physical data on the summer aerosol in the central Arctic. These data are the only surface aerosol information from this region

  • 9. Heintzenberg, J.
    et al.
    Leck, C.
    Tunved, P.
    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)
  • 10.
    Held, A.
    et al.
    Univ Bayreuth, Bayreuth Ctr Ecol & Environm Res, D-95440 Bayreuth, Germany.;Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Brooks, I. M.
    Univ Leeds, Sch Earth & Environm, Leeds LS2 9JT, W Yorkshire, England..
    Leck, C.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Tjernström, M.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    On the potential contribution of open lead particle emissions to the central Arctic aerosol concentration2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 7, p. 3093-3105Article in journal (Refereed)
    Abstract [en]

    We present direct eddy covariance measurements of aerosol number fluxes, dominated by sub-50 nm particles, at the edge of an ice floe drifting in the central Arctic Ocean. The measurements were made during the ice-breaker borne ASCOS (Arctic Summer Cloud Ocean Study) expedition in August 2008 between 2 degrees-10 degrees W longitude and 87 degrees-87.5 degrees N latitude. The median aerosol transfer velocities over different surface types (open water leads, ice ridges, snow and ice surfaces) ranged from 0.27 to 0.68 mm s(-1) during deposition-dominated episodes. Emission periods were observed more frequently over the open lead, while the snow behaved primarily as a deposition surface. Directly measured aerosol fluxes were compared with particle deposition parameterizations in order to estimate the emission flux from the observed net aerosol flux. Finally, the contribution of the open lead particle source to atmospheric variations in particle number concentration was evaluated and compared with the observed temporal evolution of particle number. The direct emission of aerosol particles from the open lead can explain only 5-10% of the observed particle number variation in the mixing layer close to the surface.

  • 11. Hirdman, D.
    et al.
    Burkhart, J. F.
    Sodemann, H.
    Eckhardt, S.
    Jefferson, A.
    NOAA, ESRL, Global Monitoring Div, Silver Spring, MD USA.;Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA..
    Quinn, P. K.
    NOAA, PMEL, Silver Spring, MD USA..
    Sharma, S.
    Ström, J.
    Norwegian Polar Res Inst, Tromso, Norway..
    Stohl, A.
    Long-term trends of black carbon and sulphate aerosol in the Arctic: changes in atmospheric transport and source region emissions2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 19, p. 9351-9368Article in journal (Refereed)
    Abstract [en]

    As a part of the IPY project POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols and Transport) and building on previous work (Hirdman et al., 2010), this paper studies the long-term trends of both atmospheric transport as well as equivalent black carbon (EBC) and sulphate for the three Arctic stations Alert, Barrow and Zeppelin. We find a general downward trend in the measured EBC concentrations at all three stations, with a decrease of -2.1 +/- 0.4 ng m(-3) yr(-1) (for the years 1989-2008) and -1.4 +/- 0.8 ng m(-3) yr(-1) (2002-2009) at Alert and Zeppelin respectively. The decrease at Barrow is, however, not statistically significant. The measured sulphate concentrations show a decreasing trend at Alert and Zeppelin of -15 +/- 3 ng m(-3) yr(-1) (1985-2006) and -1.3 +/- 1.2 ng m(-3) yr(-1) (1990-2008) respectively, while there is no trend detectable at Barrow. To reveal the contribution of different source regions on these trends, we used a cluster analysis of the output of the Lagrangian particle dispersion model FLEXPART run backward in time from the measurement stations. We have investigated to what extent variations in the atmospheric circulation, expressed as variations in the frequencies of the transport from four source regions with different emission rates, can explain the long-term trends in EBC and sulphate measured at these stations. We find that the long-term trend in the atmospheric circulation can only explain a minor fraction of the overall downward trend seen in the measurements of EBC (0.3-7.2%) and sulphate (0.3-5.3%) at the Arctic stations. The changes in emissions are dominant in explaining the trends. We find that the highest EBC and sulphate concentrations are associated with transport from Northern Eurasia and decreasing emissions in this region drive the downward trends. Northern Eurasia (cluster: NE, WNE and ENE) is the dominant emission source at all Arctic stations for both EBC and sulphate during most seasons. In wintertime, there are indications that the EBC emissions from the eastern parts of Northern Eurasia (ENE cluster) have increased over the last decade.

  • 12.
    Hirdman, D.
    et al.
    Norwegian Inst Air Res NILU, Trondheim, Norway..
    Sodemann, H.
    Norwegian Inst Air Res NILU, Trondheim, Norway..
    Eckhardt, S.
    Norwegian Inst Air Res NILU, Trondheim, Norway..
    Burkhart, J. F.
    Norwegian Inst Air Res NILU, Trondheim, Norway..
    Jefferson, A.
    NOAA, ESRL, Global Monitoring Div, Washington, DC USA.;Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA..
    Mefford, T.
    NOAA, ESRL, Global Monitoring Div, Washington, DC USA.;Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA..
    Quinn, P. K.
    NOAA, PMEL, Washington, DC USA..
    Sharma, S.
    Ström, J.
    Norwegian Polar Res Inst, Tromso, Norway..
    Stohl, A.
    Norwegian Inst Air Res NILU, Trondheim, Norway..
    Source identification of short-lived air pollutants in the Arctic using statistical analysis of measurement data and particle dispersion model output2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 2, p. 669-693Article in journal (Refereed)
    Abstract [en]

    As a part of the IPY project POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate Chemistry, Aerosols and Transport), this paper studies the sources of equivalent black carbon (EBC), sulphate, light-scattering aerosols and ozone measured at the Arctic stations Zeppelin, Alert, Barrow and Summit during the years 2000-2007. These species are important pollutants and climate forcing agents, and sulphate and EBC are main components of Arctic haze. To determine where these substances originate, the measurement data were combined with calculations using FLEXPART, a Lagrangian particle dispersion model. The climatology of atmospheric transport from surrounding regions on a twenty-day time scale modelled by FLEXPART shows that the stations Zeppelin, Alert and Barrow are highly sensitive to surface emissions in the Arctic and to emissions in high-latitude Eurasia in winter. Emission sensitivities over southern Asia and southern North America are small throughout the year. The high-altitude station Summit is an order of magnitude less sensitive to surface emissions in the Arctic whereas emissions in the southern parts of the Northern Hemisphere continents are more influential relative to the other stations. Our results show that for EBC and sulphate measured at Zeppelin, Alert and Barrow, northern Eurasia is the dominant source region. For sulphate, Eastern Europe and the metal smelting industry in Norilsk are particularly important. For EBC, boreal forest fires also contribute in summer. No evidence for any substantial contribution to EBC from sources in southern Asia is found. European air masses are associated with low ozone concentrations in winter due to titration by nitric oxides, but are associated with high ozone concentrations in summer due to photochemical ozone formation. There is also a strong influence of ozone depletion events in the Arctic boundary layer on measured ozone concentrations in spring and summer. These results will be useful for developing emission reduction strategies for the Arctic.

  • 13.
    Khosrawi, F.
    et al.
    Stockholm Univ, MISU, S-10691 Stockholm, Sweden..
    Ström, J.
    Norwegian Polar Res Inst, Tromso, Norway..
    Minikin, A.
    DLR, Oberpfaffenhofen, Germany..
    Krejci, R.
    Stockholm Univ, ITM, S-10691 Stockholm, Sweden..
    Particle formation in the Arctic free troposphere during the ASTAR 2004 campaign: a case study on the influence of vertical motion on the binary homogeneous nucleation of H2SO4/H2O2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 3, p. 1105-1120Article in journal (Refereed)
    Abstract [en]

    During the ASTAR (Arctic Study of Tropospheric Aerosol and Radiation) campaign nucleation mode particles (4 to 13 nm) were quite frequently observed at altitudes below 4000 m. However, in the upper free troposphere, nucleation mode particles were only observed once, namely during the flight on 24 May 2004 (7000 m). To investigate if vertical motion were the reason for this difference that on one particular day nucleation mode particles were observed but not on the other days we employ a microphysical box model. The box model simulations were performed along air parcel trajectories calculated 6-d backwards based on European Center for Medium-Range Weather Forecasts (ECMWF) meteorological analyses using state parameters such as pressure and temperature in combination with additional parameters such as vertical stability. Box model simulations were performed for the 24 May where nucleation mode particles were observed (nucleation event) as well as for the days with measurements before and after (22 and 26 May) which are representative for no nucleation (non-nucleation event). A nucleation burst was simulated along all trajectories, however, in the majority of the simulations the nucleation rate was either too low or too high so that no nucleation mode particles were left at the time when the measurements were performed. Further, the simulation results could be divided into three cases. Thereby, we found that for case 1 the temperature was the only driving mechanism for the formation of new particles while for case 2 and 3 vertical motion have influenced the formation of new particles. The reason why nucleation mode particles were observed on 24 May, but not on the other days, can be explained by the conditions under which particle formation occurred. On 24 May the particle formation was caused by a slow updraft, while on the other two days the particle formation was caused by a fast updraft.

  • 14.
    Kupiszewski, P.
    et al.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden.;Paul Scherrer Inst, Lab Atmospher Chem, CH-5232 Villigen, Switzerland..
    Leck, C.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Tjernström, M.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Sjogren, S.
    Lund Univ, Dept Phys, S-22362 Lund, Sweden..
    Sedlar, J.
    Swedish Meteorol & Hydrol Inst, Remote Sensing Div, S-60176 Norrkoping, Sweden..
    Graus, M.
    Univ Colorado, CIRES, Boulder, CO 80309 USA.;NOAA, Earth Sci Res Lab, Div Chem Sci, Boulder, CO 80305 USA..
    Mueller, M.
    Univ Innsbruck, Inst Ion & Appl Phys, A-6020 Innsbruck, Austria..
    Brooks, B.
    Natl Ctr Atmospher Sci, Leeds, W Yorkshire, England..
    Swietlicki, E.
    Lund Univ, Dept Phys, S-22362 Lund, Sweden..
    Norris, S.
    Univ Leeds, Sch Earth & Environm, Inst Climate & Atmospher Sci, Leeds LS2 9JT, W Yorkshire, England..
    Hansel, A.
    Univ Innsbruck, Inst Ion & Appl Phys, A-6020 Innsbruck, Austria..
    Vertical profiling of aerosol particles and trace gases over the central Arctic Ocean during summer2013In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, no 24, p. 12405-12431Article in journal (Refereed)
    Abstract [en]

    Unique measurements of vertical size-resolved aerosol particle concentrations, trace gas concentrations and meteorological data were obtained during the Arctic Summer Cloud Ocean Study (ASCOS, www.ascos.se), an International Polar Year project aimed at establishing the processes responsible for formation and evolution of low-level clouds over the high Arctic summer pack ice. The experiment was conducted from on board the Swedish icebreaker Oden, and provided both ship-and helicopter-based measurements. This study focuses on the vertical helicopter profiles and onboard measurements obtained during a three-week period when Oden was anchored to a drifting ice floe, and sheds light on the characteristics of Arctic aerosol particles and their distribution throughout the lower atmosphere. Distinct differences in aerosol particle characteristics within defined atmospheric layers are identified. Within the lowermost couple hundred metres, transport from the marginal ice zone (MIZ), condensational growth and cloud processing develop the aerosol population. During two of the four representative periods defined in this study, such influence is shown. At altitudes above about 1 km, long-range transport occurs frequently. However, only infrequently does large-scale subsidence descend such air masses to become entrained into the mixed layer in the high Arctic, and there-fore long-range transport plumes are unlikely to directly influence low-level stratiform cloud formation. Nonetheless, such plumes can influence the radiative balance of the planetary boundary layer (PBL) by influencing formation and evolution of higher clouds, as well as through precipitation transport of particles downwards. New particle formation was occasionally observed, particularly in the near-surface layer. We hypothesize that the origin of these ultrafine particles could be in biological processes, both primary and secondary, within the open leads between the pack ice and/or along the MIZ. In general, local sources, in combination with upstream boundary-layer transport of precursor gases from the MIZ, are considered to constitute the origin of cloud condensation nuclei (CCN) particles and thus be of importance for the formation of interior Arctic low-level clouds during summer, and subsequently, through cloud influences, for the melting and freezing of sea ice.

  • 15. Leck, C.
    et al.
    Gao, Q.
    Mashayekhy Rad, F.
    Nilsson, U.
    Size-resolved atmospheric particulate polysaccharides in the high summer Arctic2013In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, no 24, p. 12573-12588Article in journal (Refereed)
    Abstract [en]

    Size-resolved aerosol samples for subsequent quantitative determination of polymer sugars (polysaccharides) after hydrolysis to their subunit monomers (monosaccharides) were collected in surface air over the central Arctic Ocean during the biologically most active summer period. The analysis was carried out by novel use of liquid chromatography coupled with highly selective and sensitive tandem mass spectrometry. Polysaccharides were detected in particle sizes ranging from 0.035 to 10 μm in diameter with distinct features of heteropolysaccharides, enriched in xylose, glucose + mannose as well as a substantial fraction of deoxysugars. Polysaccharides, containing deoxysugar monomers, showed a bimodal size structure with about 70% of their mass found in the Aitken mode over the pack ice area. Pentose (xylose) and hexose (glucose + mannose) had a weaker bimodal character and were largely found with super-micrometer sizes and in addition with a minor sub-micrometer fraction. The concentration of total hydrolysable neutral sugars (THNS) in the samples collected varied over two orders of magnitude (1 to 160 pmol m−3) in the super-micrometer size fraction and to a somewhat lesser extent in sub-micrometer particles (4 to 140 pmol m−3). Lowest THNS concentrations were observed in air masses that had spent more than five days over the pack ice. Within the pack ice area, about 53% of the mass of hydrolyzed polysaccharides was detected in sub-micrometer particles. The relative abundance of sub-micrometer hydrolyzed polysaccharides could be related to the length of time that the air mass spent over pack ice, with the highest fraction (> 90%) observed for > 7 days of advection. The aerosol samples collected onboard ship showed similar monosaccharide composition, compared to particles generated experimentally in situ at the expedition's open lead site. This supports the existence of a primary particle source of polysaccharide containing polymer gels from open leads by bubble bursting at the air–sea interface. We speculate that the occurrence of atmospheric surface-active polymer gels with their hydrophilic and hydrophobic segments, promoting cloud droplet activation, could play a potential role as cloud condensation nuclei in the pristine high Arctic.

  • 16. Leck, C.
    et al.
    Svensson, E.
    Importance of aerosol composition and mixing state for cloud droplet activation over the Arctic pack ice in summer2015In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 15, no 5, p. 2545-2568Article in journal (Refereed)
  • 17. Li, X.
    et al.
    Hede, T.
    Tu, Y.
    Leck, C.
    Agren, H.
    Glycine in aerosol water droplets: a critical assessment of Kohler theory by predicting surface tension from molecular dynamics simulations2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 2, p. 519-527Article in journal (Refereed)
    Abstract [en]

    Aerosol particles in the atmosphere are important participants in the formation of cloud droplets and have significant impact on cloud albedo and global climate. According to the Kohler theory which describes the nucleation and the equilibrium growth of cloud droplets, the surface tension of an aerosol droplet is one of the most important factors that determine the critical supersaturation of droplet activation. In this paper, with specific interest to remote marine aerosol, we predict the surface tension of aerosol droplets by performing molecular dynamics simulations on two model systems, the pure water droplets and glycine in water droplets. The curvature dependence of the surface tension is interpolated by a quadratic polynomial over the nano-sized droplets and the limiting case of a planar interface, so that the so-called Aitken mode particles which are critical for droplet formation could be covered and the Kohler equation could be improved by incorporating surface tension corrections.

  • 18. Martin, M.
    et al.
    Chang, R. Y. -W
    Sierau, B.
    Sjögren, S.
    Swietlicki, E.
    Abbatt, J. P. D.
    Leck, C.
    Lohmann, U.
    Cloud condensation nuclei closure study on summer arctic aerosol2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 22, p. 11335-11350Article in journal (Refereed)
    Abstract [en]

    We present an aerosol – cloud condensation nuclei (CCN) closure study on summer high Arctic aerosol based on measurements that were carried out in 2008 during the Arctic Summer Cloud Ocean Study (ASCOS) on board the Swedish ice breaker Oden. The data presented here were collected during a three-week time period in the pack ice (>85° N) when the icebreaker Oden was moored to an ice floe and drifted passively during the most biological active period into autumn freeze up conditions. 

    CCN number concentrations were obtained using two CCN counters measuring at different supersaturations. The directly measured CCN number concentration was then compared with a CCN number concentration calculated using both bulk aerosol mass composition data from an aerosol mass spectrometer (AMS) and aerosol number size distributions obtained from a differential mobility particle sizer, assuming κ-Köhler theory, surface tension of water and an internally mixed aerosol. The last assumption was supported by measurements made with a hygroscopic tandem differential mobility analyzer (HTDMA) for particles >70 nm.

    For the two highest measured supersaturations, 0.73 and 0.41%, closure could not be achieved with the investigated settings concerning hygroscopicity and density. The calculated CCN number concentration was always higher than the measured one for those two supersaturations. This might be caused by a relative larger insoluble organic mass fraction of the smaller particles that activate at these supersaturations, which are thus less good CCN than the larger particles. On average, 36% of the mass measured with the AMS was organic mass. At 0.20, 0.15 and 0.10% supersaturation, closure could be achieved with different combinations of hygroscopic parameters and densities within the uncertainty range of the fit. The best agreement of the calculated CCN number concentration with the observed one was achieved when the organic fraction of the aerosol was treated as nearly water insoluble (κorg=0.02), leading to a mean total κ, κtot, of 0.33 ± 0.13. However, several settings led to closure and κorg=0.2 is found to be an upper limit at 0.1% supersaturation. κorg≤0.2 leads to a κtot range of 0.33 ± 013 to 0.50 ± 0.11. Thus, the organic material ranges from being sparingly soluble to effectively insoluble. These results suggest that an increase in organic mass fraction in particles of a certain size would lead to a suppression of the Arctic CCN activity.

  • 19.
    Mauritsen, T.
    et al.
    Max Planck Inst Meteorol, Hamburg, Germany..
    Sedlar, J.
    Bert Bolin Ctr Climate Res, Stockholm, Sweden.;Stockholm Univ, S-10691 Stockholm, Sweden..
    Tjernström, M.
    Bert Bolin Ctr Climate Res, Stockholm, Sweden.;Stockholm Univ, S-10691 Stockholm, Sweden..
    Leck, C.
    Bert Bolin Ctr Climate Res, Stockholm, Sweden.;Stockholm Univ, S-10691 Stockholm, Sweden..
    Martin, M.
    ETH, Inst Atmospher & Climate Sci, Zurich, Switzerland..
    Shupe, M.
    Univ Colorado, Boulder, CO 80309 USA.;NOAA ESRL, Boulder, CO USA..
    Sjögren, S.
    Lund Univ, Lund, Sweden..
    Sierau, B.
    ETH, Inst Atmospher & Climate Sci, Zurich, Switzerland..
    Persson, P. O. G.
    Univ Colorado, Boulder, CO 80309 USA.;NOAA ESRL, Boulder, CO USA..
    Brooks, I. M.
    Univ Leeds, Leeds, W Yorkshire, England..
    Swietlicki, E.
    Lund Univ, Lund, Sweden..
    An Arctic CCN-limited cloud-aerosol regime2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 1, p. 165-173Article in journal (Refereed)
    Abstract [en]

    On average, airborne aerosol particles cool the Earth's surface directly by absorbing and scattering sunlight and indirectly by influencing cloud reflectivity, life time, thickness or extent. Here we show that over the central Arctic Ocean, where there is frequently a lack of aerosol particles upon which clouds may form, a small increase in aerosol loading may enhance cloudiness thereby likely causing a climatologically significant warming at the ice-covered Arctic surface. Under these low concentration conditions cloud droplets grow to drizzle sizes and fall, even in the absence of collisions and coalescence, thereby diminishing cloud water. Evidence from a case study suggests that interactions between aerosol, clouds and precipitation could be responsible for attaining the observed low aerosol concentrations.

  • 20. Partanen, A. I.
    et al.
    Laakso, A.
    Schmidt, A.
    Kokkola, H.
    Kuokkanen, T.
    Pietikäinen, J. -P
    Kerminen, V. -M
    Lehtinen, K. E. J.
    Laakso, L.
    Korhonen, H.
    Climate and air quality trade-offs in altering ship fuel sulfur content2013In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, no 23, p. 12059-12071Article in journal (Refereed)
    Abstract [en]

    Aerosol particles from shipping emissions both cool the climate and cause adverse health effects. The cooling effect is, however, declining because of shipping emission controls aiming to improve air quality. We used an aerosol-climate model ECHAM-HAMMOZ to test whether by altering ship fuel sulfur content, the present-day aerosol-induced cooling effect from shipping could be preserved, while at the same time reducing premature mortality rates related to shipping emissions. We compared the climate and health effects of a present-day shipping emission scenario (ship fuel sulfur content of 2.7%) with (1) a simulation with strict emission controls in the coastal waters (ship fuel sulfur content of 0.1%) and twofold the present-day fuel sulfur content (i.e. 5.4%) elsewhere; and (2) a scenario with global strict shipping emission controls (ship fuel sulfur content of 0.1% in coastal waters and 0.5% elsewhere) roughly corresponding to international agreements to be enforced by the year 2020. Scenario 1 had a slightly stronger aerosol-induced effective radiative forcing (ERF) from shipping than the present-day scenario (−0.43 W m−2 vs. −0.39 W m−2) while reducing premature mortality from shipping by 69% (globally 34 900 deaths avoided per year). Scenario 2 decreased the ERF to −0.06 W m−2 and annual deaths by 96% (globally 48 200 deaths avoided per year) compared to present-day. Our results show that the cooling effect of present-day emissions could be retained with simultaneous notable improvements in air quality, even though the shipping emissions from the open ocean clearly have a significant effect on continental air quality. However, increasing ship fuel sulfur content in the open ocean would violate existing international treaties, could cause detrimental side-effects, and could be classified as geoengineering.

  • 21.
    Rastak, N.
    et al.
    Stockholm Univ, Dept Appl Environm Sci ITM, S-11418 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-11418 Stockholm, Sweden..
    Silvergren, S.
    Lund Univ, Div Nucl Phys, SE-21100 Lund, Sweden..
    Zieger, P.
    Stockholm Univ, Dept Appl Environm Sci ITM, S-11418 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-11418 Stockholm, Sweden..
    Wideqvist, U.
    Stockholm Univ, Dept Appl Environm Sci ITM, S-11418 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-11418 Stockholm, Sweden..
    Ström, J.
    Stockholm Univ, Dept Appl Environm Sci ITM, S-11418 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-11418 Stockholm, Sweden..
    Svenningsson, B.
    Lund Univ, Div Nucl Phys, SE-21100 Lund, Sweden..
    Maturilli, M.
    Helmholtz Ctr Polar & Marine Res, Alfred Wegener Inst, D-14473 Potsdam, Germany..
    Tesche, M.
    Stockholm Univ, Dept Appl Environm Sci ITM, S-11418 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-11418 Stockholm, Sweden..
    Ekman, A. M. L.
    Stockholm Univ, Dept Meteorol MISU, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Tunved, P.
    Stockholm Univ, Dept Appl Environm Sci ITM, S-11418 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-11418 Stockholm, Sweden..
    Riipinen, I.
    Stockholm Univ, Dept Appl Environm Sci ITM, S-11418 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-11418 Stockholm, Sweden..
    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).

  • 22.
    Ruppel, M. M.
    et al.
    Univ Helsinki, Dept Environm Sci, Helsinki, Finland..
    Isaksson, I.
    Norwegian Polar Res Inst, Tromso, Norway..
    Ström, J.
    Stockholm Univ, Atmospher Sci Unit, Dept Appl Environm Sci ITM, S-10691 Stockholm, Sweden..
    Beaudon, E.
    Ohio State Univ, Byrd Polar Res Ctr, Columbus, OH 43210 USA..
    Svensson, J.
    Univ Helsinki, Dept Environm Sci, Helsinki, Finland.;FMI, Helsinki, Finland..
    Pedersen, C. A.
    Norwegian Polar Res Inst, Tromso, Norway..
    Korhola, A.
    Univ Helsinki, Dept Environm Sci, Helsinki, Finland..
    Increase in elemental carbon values between 1970 and 2004 observed in a 300-year ice core from Holtedahlfonna (Svalbard)2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 20, p. 11447-11460Article in journal (Refereed)
    Abstract [en]

    Black carbon (BC) is a light-absorbing particle that warms the atmosphere-Earth system. The climate effects of BC are amplified in the Arctic, where its deposition on light surfaces decreases the albedo and causes earlier melt of snow and ice. Despite its suggested significant role in Arctic climate warming, there is little information on BC concentrations and deposition in the past. Here we present results on BC (here operationally defined as elemental carbon (EC)) concentrations and deposition on a Svalbard glacier between 1700 and 2004. The inner part of a 125m deep ice core from Holtedahlfonna glacier (79 degrees 8'N, 13 degrees 16'E, 1150 m a.s.l.) was melted, filtered through a quartz fibre filter and analysed for EC using a thermal-optical method. The EC values started to increase after 1850 and peaked around 1910, similar to ice core records from Greenland. Strikingly, the EC values again increase rapidly between 1970 and 2004 after a temporary low point around 1970, reaching unprecedented values in the 1990s. This rise is not seen in Greenland ice cores, and it seems to contradict atmospheric BC measurements indicating generally decreasing atmospheric BC concentrations since 1989 in the Arctic. For example, changes in scavenging efficiencies, post-depositional processes and differences in the vertical distribution of BC in the atmosphere are discussed for the differences between the Svalbard and Greenland ice core records, as well as the ice core and atmospheric measurements in Svalbard. In addition, the divergent BC trends between Greenland and Svalbard ice cores may be caused by differences in the analytical methods used, including the operational definitions of quantified particles, and detection efficiencies of different-sized BC particles. Regardless of the cause of the increasing EC values between 1970 and 2004, the results have significant implications for the past radiative energy balance at the coring site.

  • 23. Sedlar, J.
    et al.
    Shupe, M. D.
    Characteristic nature of vertical motions observed in Arctic mixed-phase stratocumulus2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 7, p. 3461-3478Article in journal (Refereed)
    Abstract [en]

    Over the Arctic Ocean, little is known on cloud-generated buoyant overturning vertical motions within mixed-phase stratocumulus clouds. Characteristics of such motions are important for understanding the diabatic processes associated with the vertical motions, the lifetime of the cloud layer and its micro- and macrophysical characteristics. In this study, we exploit a suite of surface-based remote sensors over the high-Arctic sea ice during a weeklong period of persistent stratocumulus in August 2008 to derive the in-cloud vertical motion characteristics. In-cloud vertical velocity skewness and variance profiles are found to be strikingly different from observations within lower-latitude stratocumulus, suggesting these Arctic mixed-phase clouds interact differently with the atmospheric thermodynamics (cloud tops extending above a stable temperature inversion base) and with a different coupling state between surface and cloud. We find evidence of cloud-generated vertical mixing below cloud base, regardless of surface–cloud coupling state, although a decoupled surface–cloud state occurred most frequently. Detailed case studies are examined, focusing on three levels within the cloud layer, where wavelet and power spectral analyses are applied to characterize the dominant temporal and horizontal scales associated with cloud-generated vertical motions. In general, we find a positively correlated vertical motion signal amongst vertical levels within the cloud and across the full cloud layer depth. The coherency is dependent upon other non-cloud controlled factors, such as larger, mesoscale weather passages and radiative shielding of low-level stratocumulus by one or more cloud layers above. Despite the coherency in vertical velocity across the cloud, the velocity variances were always weaker near cloud top, relative to cloud middle and base. Taken in combination with the skewness, variance and thermodynamic profile characteristics, we observe vertical motions near cloud top that behave differently than those from lower within the cloud layer. Spectral analysis indicates peak cloud-generated w variance timescales slowed only modestly during decoupled cases relative to coupled; horizontal wavelengths only slightly increased when transitioning from coupling to decoupling. The similarities in scales suggests that perhaps the dominant forcing for all cases is generated from the cloud layer, and it is not the surface forcing that characterizes the time- and space scales of in-cloud vertical velocity variance. This points toward the resilient nature of Arctic mixed-phase clouds to persist when characterized by thermodynamic regimes unique to the Arctic.

  • 24.
    Shupe, M. D.
    et al.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Earth Syst Res Lab, Boulder, CO USA..
    Persson, P. O. G.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Earth Syst Res Lab, Boulder, CO USA..
    Brooks, I. M.
    Univ Leeds, Inst Climate & Atmospher Sci, Leeds, W Yorkshire, England..
    Tjernström, M.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Sedlar, J.
    Swedish Meteorol & Hydrol Inst, S-60176 Norrkoping, Sweden..
    Mauritsen, T.
    Max Planck Inst Meteorol, D-20146 Hamburg, Germany..
    Sjögren, S.
    Lund Univ, Dept Phys, S-22362 Lund, Sweden..
    Leck, C.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Cloud and boundary layer interactions over the Arctic sea ice in late summer2013In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, no 18, p. 9379-9399Article in journal (Refereed)
    Abstract [en]

    Observations from the Arctic Summer Cloud Ocean Study (ASCOS), in the central Arctic sea-ice pack in late summer 2008, provide a detailed view of cloud-atmosphere-surface interactions and vertical mixing processes over the sea-ice environment. Measurements from a suite of ground-based remote sensors, near-surface meteorological and aerosol instruments, and profiles from radiosondes and a helicopter are combined to characterize a week-long period dominated by low-level, mixed-phase, stratocumulus clouds. Detailed case studies and statistical analyses are used to develop a conceptual model for the cloud and atmosphere structure and their interactions in this environment. Clouds were persistent during the period of study, having qualities that suggest they were sustained through a combination of advective influences and in-cloud processes, with little contribution from the surface. Radiative cooling near cloud top produced buoyancy-driven, turbulent eddies that contributed to cloud formation and created a cloud-driven mixed layer. The depth of this mixed layer was related to the amount of turbulence and condensed cloud water. Coupling of this cloud-driven mixed layer to the surface boundary layer was primarily determined by proximity. For 75% of the period of study, the primary stratocumulus cloud-driven mixed layer was decoupled from the surface and typically at a warmer potential temperature. Since the near-surface temperature was constrained by the ocean-ice mixture, warm temperatures aloft suggest that these air masses had not significantly interacted with the sea-ice surface. Instead, back-trajectory analyses suggest that these warm air masses advected into the central Arctic Basin from lower latitudes. Moisture and aerosol particles likely accompanied these air masses, providing necessary support for cloud formation. On the occasions when cloud-surface coupling did occur, back trajectories indicated that these air masses advected at low levels, while mixing processes kept the mixed layer in equilibrium with the near-surface environment. Rather than contributing buoyancy forcing for the mixed-layer dynamics, the surface instead simply appeared to respond to the mixed-layer processes aloft. Clouds in these cases often contained slightly higher condensed water amounts, potentially due to additional moisture sources from below.

  • 25. Sierau, B.
    et al.
    Chang, R. Y. -W
    Leck, C.
    Paatero, J.
    Lohmann, U.
    Single-particle characterization of the high-Arctic summertime aerosol2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 14, p. 7409-7430Article in journal (Refereed)
    Abstract [en]

     Single-particle mass-spectrometric measurements were carried out in the high Arctic north of 80° during summer 2008. The campaign took place onboard the icebreaker Oden and was part of the Arctic Summer Cloud Ocean Study (ASCOS). The instrument deployed was an aerosol time-of-flight mass spectrometer (ATOFMS) that provides information on the chemical composition of individual particles and their mixing state in real time. Aerosols were sampled in the marine boundary layer at stations in the open ocean, in the marginal ice zone, and in the pack ice region. The largest fraction of particles detected for subsequent analysis in the size range of the ATOFMS between approximately 200 and 3000 nm in diameter showed mass-spectrometric patterns, indicating an internal mixing state and a biomass burning and/or biofuel source. The majority of these particles were connected to an air mass layer of elevated particle concentration mixed into the surface mixed layer from the upper part of the marine boundary layer. The second largest fraction was represented by sea salt particles. The chemical analysis of the over-ice sea salt aerosol revealed tracer compounds that reflect chemical aging of the particles during their long-range advection from the marginal ice zone, or open waters south thereof prior to detection at the ship. From our findings we conclude that long-range transport of particles is one source of aerosols in the high Arctic. To assess the importance of long-range particle sources for aerosol–cloud interactions over the inner Arctic in comparison to local and regional biogenic primary aerosol sources, the chemical composition of the detected particles was analyzed for indicators of marine biological origin. Only a minor fraction showed chemical signatures of potentially ocean-derived primary particles of that kind. However, a chemical bias in the ATOFMS's detection capabilities observed during ASCOS might suggest the presence of a particle type of unknown composition and source. In general, the study suffered from low counting statistics due to the overall small number of particles found in this pristine environment, the small sizes of the prevailing aerosol below the detection limit of the ATOFMS, and its low hit rate. To our knowledge, this study reports on the first in situ single-particle mass-spectrometric measurements in the marine boundary layer of the high-Arctic pack ice region.

  • 26.
    Skeie, R. B.
    et al.
    Ctr Int Climate & Environm Res Oslo CICERO, Oslo, Norway..
    Berntsen, T.
    Ctr Int Climate & Environm Res Oslo CICERO, Oslo, Norway.;Univ Oslo, Dept Geosci, Oslo, Norway..
    Myhre, G.
    Ctr Int Climate & Environm Res Oslo CICERO, Oslo, Norway..
    Pedersen, C. A.
    Fram Ctr, Norwegian Polar Inst, Tromso, Norway..
    Ström, J.
    Fram Ctr, Norwegian Polar Inst, Tromso, Norway..
    Gerland, S.
    Fram Ctr, Norwegian Polar Inst, Tromso, Norway..
    Ogren, J. A.
    Natl Ocean & Atmospher Adm, Earth Syst Res Lab, Boulder, CO USA..
    Black carbon in the atmosphere and snow, from pre-industrial times until present2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 14, p. 6809-6836Article in journal (Refereed)
    Abstract [en]

    The distribution of black carbon (BC) in the atmosphere and the deposition of BC on snow surfaces since pre-industrial time until present are modelled with the Oslo CTM2 model. The model results are compared with observations including recent measurements of BC in snow in the Arctic. The global mean burden of BC from fossil fuel and biofuel sources increased during two periods. The first period, until 1920, is related to increases in emissions in North America and Europe, and the last period after 1970 are related mainly to increasing emissions in East Asia. Although the global burden of BC from fossil fuel and biofuel increases, in the Arctic the maximum atmospheric BC burden as well as in the snow was reached in 1960s, with a slight reduction thereafter. The global mean burden of BC from open biomass burning sources has not changed significantly since 1900. With current inventories of emissions from open biomass sources, the modelled burden of BC in snow and in the atmosphere north of 65 degrees N is small compared to the BC burden of fossil fuel and biofuel origin. From the concentration changes radiative forcing time series due to the direct aerosol effect as well as the snow-albedo effect is calculated for BC from fossil fuel and biofuel. The calculated radiative forcing in 2000 for the direct aerosol effect is 0.35 W m(-2) and for the snow-albedo effect 0.016 W m(-2) in this study. Due to a southward shift in the emissions there is an increase in the lifetime of BC as well as an increase in normalized radiative forcing, giving a change in forcing per unit of emissions of 26% since 1950.

  • 27. Sommar, J.
    et al.
    Andersson, M. E.
    Jacobi, H-W
    Circumpolar measurements of speciated mercury, ozone and carbon monoxide in the boundary layer of the Arctic Ocean2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 11, p. 5031-5045Article in journal (Refereed)
    Abstract [en]

    Using the Swedish icebreaker Oden as a platform, continuous measurements of airborne mercury (gaseous elemental mercury (Hg-0), divalent gaseous mercury species (HgX2)-X-II(g) (acronym RGM) and mercury attached to particles (PHg)) and some long-lived trace gases (carbon monoxide CO and ozone O-3) were performed over the North Atlantic and the Arctic Ocean. The measurements were performed for nearly three months (July-September 2005) during the Beringia 2005 expedition (from Goteborg, Sweden via the proper Northwest Passage to the Beringia region Alaska - Chukchi Penninsula - Wrangel Island and in-turn via a north-polar transect to Longyearbyen, Spitsbergen). The Beringia 2005 expedition was the first time that these species have been measured during summer over the Arctic Ocean going from 60 degrees to 90 degrees N. During the North Atlantic transect, concentration levels of Hg-0, CO and O-3 were measured comparable to typical levels for the ambient mid-hemispheric average. However, a rapid increase of Hg-0 in air and surface water was observed when entering the ice-covered waters of the Canadian Arctic archipelago. Large parts of the measured waters were supersaturated with respect to Hg-0, reflecting a strong disequilibrium. Heading through the sea ice of the Arctic Ocean, a fraction of the strong Hg-0 pulse in the water was transferred with some time-delay into the air samples collected similar to 20m above sea level. Several episodes of elevated Hg-0 in air were encountered along the sea ice route with higher mean concentration (1.81 +/- 0.43 ng m(-3)) compared to the marine boundary layer over ice-free Arctic oceanic waters (1.55 +/- 0.21 ng m(-3)). In addition, the bulk of the variance in the temporal series of Hg-0 concentrations was observed during July. The Oden Hg-0 observations compare in this aspect very favourably with those at the coastal station Alert. Atmospheric boundary layer O-3 mixing ratios decreased when initially sailing northward. In the Arctic, an O-3 minimum around 15-20 ppbV was observed during summer (July-August). Alongside the polar transect during the beginning of autumn, a steady trend of increasing O-3 mixing ratios was measured returning to initial levels of the expedition (> 30 ppbV). Ambient CO was fairly stable (84 +/- 12 ppbV) during the expedition. However, from the Beaufort Sea and moving onwards steadily increasing CO mixing ratios were observed (0.3 ppbV day(-1)). On a comparison with coeval archived CO and O-3 data from the Arctic coastal strip monitoring sites Barrow and Alert, the observations from Oden indicate these species to be homogeneously distributed over the Arctic Ocean. Neither correlated low ozone and Hg-0 events nor elevated concentrations of RGM and PHg were at any extent sampled, suggesting that atmospheric mercury deposition to the Arctic basin is low during the Polar summer and autumn.

  • 28. Sommar, J.
    et al.
    Wängberg, I.
    Berg, T.
    Gårdfeldt, K.
    Munthe, J.
    Richter, A.
    Urba, A.
    Wittrock, F.
    Schroeder, W. H.
    Circumpolar transport and air-surface exchange of atmospheric mercury at Ny-Alesund (79 degrees N), Svalbard, spring 20022007In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 7, p. 151-166Article in journal (Refereed)
    Abstract [en]

    Mercury in different environmental compartments has been measured at Ny-Alesund (78 degrees 54'N, 11 degrees 53' E) during an intensive campaign, 17 April to 14 May 2002. Time-resolved speciated determination of mercury in the atmosphere and snow was conducted at the Norwegian research station at the Zeppelin mountain, 474 m above the sea level, and at the Italian research facility Dirigibile Italia, 12 m above the sea level. Total Gaseous Mercury (TGM) was present in the range < 0.1 to 2.2 ng m(-3) during the campaign. Three mercury depletion events, identified as periods with decreased TGM concentrations, were observed. At the lower altitude, TGM concentrations following such events were found to exhibit both higher magnitude and larger variability in comparison to results from the Zeppelin station. Oxidised mercury species in air and fall-out with snow as well as mercury attached to particles were also measured and their concentrations were found to be anti-correlated with TGM in air. concentrations of total Hg in snow (Hg-tot) showed a large ( similar to 15 x) increase in response to Gaseous Elemental Mercury Depletion Events (GEMDEs, range 1.5-76.5 ng L-1). Solid evidence for photo-stimulated emissions of Hg-0(g) from the snow pack in conjunction to depletion events were obtained from gradient measurements as well as from flux chamber measurements. Steep diurnal concentration variations of Hg-0(aq) in surface seawater were also found to concur with changing solar radiation. The concentration of Hg0( aq) in seawater was found to be in the range 12.2 - 70.4 pg L-1, which corresponds to supersaturation. Hence, the seawater surface constituted a source emitting elemental mercury. The concentrations of RGM ( reactive gaseous mercury), Hg-p ( particulate mercury), and BrO column densities ( detected by DOAS) were very low except for a few individual samples during the major Hg-0 depletion event. BrO vertical column densities obtained by the remote satellite ESR-2 and trajectory analysis indicate that the air masses exhibiting low Hg-0 concentrations originated from areas with high BrO densities.

  • 29.
    Sotiropoulou, G.
    et al.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Sedlar, J.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Tjernström, M.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Shupe, M. D.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA Earth Syst Res Lab, Boulder, CO USA..
    Brooks, I. M.
    Univ Leeds, Inst Climate & Atmospher Sci, Sch Earth & Environm, Leeds, W Yorkshire, England..
    Persson, P. O. G.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA Earth Syst Res Lab, Boulder, CO USA..
    The thermodynamic structure of summer Arctic stratocumulus and the dynamic coupling to the surface2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 22, p. 12573-12592Article in journal (Refereed)
    Abstract [en]

    The vertical structure of Arctic low-level clouds and Arctic boundary layer is studied, using observations from ASCOS (Arctic Summer Cloud Ocean Study), in the central Arctic, in late summer 2008. Two general types of cloud structures are examined: the "neutrally stratified" and "stably stratified" clouds. Neutrally stratified are mixed-phase clouds where radiative-cooling near cloud top produces turbulence that generates a cloud-driven mixed layer. When this layer mixes with the surface-generated turbulence, the cloud layer is coupled to the surface, whereas when such an interaction does not occur, it remains decoupled; the latter state is most frequently observed. The decoupled clouds are usually higher compared to the coupled; differences in thickness or cloud water properties between the two cases are however not found. The surface fluxes are also very similar for both states. The decoupled clouds exhibit a bimodal thermodynamic structure, depending on the depth of the sub-cloud mixed layer (SCML): clouds with shallower SCMLs are disconnected from the surface by weak inversions, whereas those that lay over a deeper SCML are associated with stronger inversions at the decoupling height. Neutrally stratified clouds generally precipitate; the evaporation/sublimation of precipitation often enhances the decoupling state. Finally, stably stratified clouds are usually lower, geometrically and optically thinner, non-precipitating liquid-water clouds, not containing enough liquid to drive efficient mixing through cloud-top cooling.

  • 30. Stohl, A.
    et al.
    Berg, T.
    Burkhart, J. F.
    Fjaeraa, A. M.
    Forster, C.
    Herber, A.
    Hov, O.
    Lunder, C.
    McMillan, W. W.
    Oltmans, S.
    Shiobara, M.
    Simpson, D.
    Solberg, S.
    Stebel, K.
    Ström, J.
    Törseth, K.
    Treffeisen, R.
    Virkkunen, K.
    Yttri, K. E.
    Arctic smoke - record high air pollution levels in the European Arctic due to agricultural fires in Eastern Europe in spring 20062007In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 7, p. 511-534Article in journal (Refereed)
    Abstract [en]

    In spring 2006, the European Arctic was abnormally warm, setting new historical temperature records. During this warm period, smoke from agricultural fires in Eastern Europe intruded into the European Arctic and caused the most severe air pollution episodes ever recorded there. This paper confirms that biomass burning ( BB) was indeed the source of the observed air pollution, studies the transport of the smoke into the Arctic, and presents an overview of the observations taken during the episode. Fire detections from the MODIS instruments aboard the Aqua and Terra satellites were used to estimate the BB emissions. The FLEXPART particle dispersion model was used to show that the smoke was transported to Spitsbergen and Iceland, which was confirmed by MODIS retrievals of the aerosol optical depth (AOD) and AIRS retrievals of carbon monoxide ( CO) total columns. Concentrations of halocarbons, carbon dioxide and CO, as well as levoglucosan and potassium, measured at Zeppelin mountain near Ny Alesund, were used to further corroborate the BB source of the smoke at Spitsbergen. The ozone (O(3)) and CO concentrations were the highest ever observed at the Zeppelin station, and gaseous elemental mercury was also elevated. A new O(3) record was also set at a station on Iceland. The smoke was strongly absorbing black carbon concentrations were the highest ever recorded at Zeppelin - and strongly perturbed the radiation transmission in the atmosphere: aerosol optical depths were the highest ever measured at Ny Alesund. We furthermore discuss the aerosol chemical composition, obtained from filter samples, as well as the aerosol size distribution during the smoke event. Photographs show that the snow at a glacier on Spitsbergen became discolored during the episode and, thus, the snow albedo was reduced. Samples of this polluted snow contained strongly elevated levels of potassium, sulphate, nitrate and ammonium ions, thus relating the discoloration to the deposition of the smoke aerosols. This paper shows that, to date, BB has been underestimated as a source of aerosol and air pollution for the Arctic, relative to emissions from fossil fuel combustion. Given its significant impact on air quality over large spatial scales and on radiative processes, the practice of agricultural waste burning should be banned in the future.

  • 31.
    Tjernström, M.
    et al.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Birch, C. E.
    Univ Leeds, Sch Earth & Environm, Inst Climate & Atmospher Sci, Leeds, W Yorkshire, England..
    Brooks, I. M.
    Univ Leeds, Sch Earth & Environm, Inst Climate & Atmospher Sci, Leeds, W Yorkshire, England..
    Shupe, M. D.
    Univ Colorado, Cooperat Inst Res Environm Sci CIRES, Boulder, CO 80309 USA.;Natl Atmospher & Ocean Adm, Div Phys Sci, Boulder, CO USA..
    Persson, P. O. G.
    Univ Colorado, Cooperat Inst Res Environm Sci CIRES, Boulder, CO 80309 USA.;Natl Atmospher & Ocean Adm, Div Phys Sci, Boulder, CO USA..
    Sedlar, J.
    Swedish Meteorol & Hydrol Inst, S-60176 Norrkoping, Sweden..
    Mauritsen, T.
    Max Planck Inst Meteorol, Hamburg, Germany..
    Leck, C.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Paatero, J.
    Finnish Meteorol Inst, FIN-00101 Helsinki, Finland..
    Szczodrak, M.
    Univ Miami, Rosensthiel Sch Marine & Atmospher Sci, Miami, FL USA..
    Wheeler, C. R.
    Univ Colorado, Cooperat Inst Res Environm Sci CIRES, Boulder, CO 80309 USA..
    Meteorological conditions in the central Arctic summer during the Arctic Summer Cloud Ocean Study (ASCOS)2012In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, no 15, p. 6863-6889Article in journal (Refereed)
    Abstract [en]

    Understanding the rapidly changing climate in the Arctic is limited by a lack of understanding of underlying strong feedback mechanisms that are specific to the Arctic. Progress in this field can only be obtained by process-level observations; this is the motivation for intensive ice-breaker-based campaigns such as the Arctic Summer Cloud-Ocean Study (ASCOS), described here. However, detailed field observations also have to be put in the context of the larger-scale meteorology, and short field campaigns have to be analysed within the context of the underlying climate state and temporal anomalies from this. To aid in the analysis of other parameters or processes observed during this campaign, this paper provides an overview of the synoptic-scale meteorology and its climatic anomaly during the ASCOS field deployment. It also provides a statistical analysis of key features during the campaign, such as key meteorological variables, the vertical structure of the lower troposphere and clouds, and energy fluxes at the surface. In order to assess the representativity of the ASCOS results, we also compare these features to similar observations obtained during three earlier summer experiments in the Arctic Ocean: the AOE-96, SHEBA and AOE-2001 expeditions. We find that these expeditions share many key features of the summertime lower troposphere. Taking ASCOS and the previous expeditions together, a common picture emerges with a large amount of low-level cloud in a well-mixed shallow boundary layer, capped by a weak to moderately strong inversion where moisture, and sometimes also cloud top, penetrate into the lower parts of the inversion. Much of the boundary-layer mixing is due to cloud-top cooling and subsequent buoyant overturning of the cloud. The cloud layer may, or may not, be connected with surface processes depending on the depths of the cloud and surface-based boundary layers and on the relative strengths of surface-shear and cloud-generated turbulence. The latter also implies a connection between the cloud layer and the free troposphere through entrainment at cloud top.

  • 32.
    Tjernström, M.
    et al.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Leck, C.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Birch, C. E.
    Univ Leeds, Sch Earth & Environm, Inst Climate & Atmospher Sci, Leeds, W Yorkshire, England..
    Bottenheim, J. W.
    Environm Canada, Toronto, ON, Canada..
    Brooks, B. J.
    Univ Leeds, Sch Earth & Environm, Inst Climate & Atmospher Sci, Leeds, W Yorkshire, England..
    Brooks, I. M.
    Univ Leeds, Sch Earth & Environm, Inst Climate & Atmospher Sci, Leeds, W Yorkshire, England..
    Backlin, L.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Chang, Y. -W
    de Leeuw, G.
    Finnish Meteorol Inst, FIN-00101 Helsinki, Finland.;Univ Helsinki, Dept Phys, Helsinki, Finland.;TNO Environm & Geosci, Dept Air Qual & Climate, Utrecht, Netherlands..
    Di Liberto, L.
    Italian Natl Res Council, ISAC, Rome, Italy..
    de la Rosa, S.
    Nansen Environm & Remote Sensing Ctr, Bergen, Norway.;Univ Bergen, Inst Geophys, Bergen, Norway..
    Granath, E.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Graus, M.
    Univ Innsbruck, Inst Ion Phys & Appl Phys, A-6020 Innsbruck, Austria..
    Hansel, A.
    Univ Innsbruck, Inst Ion Phys & Appl Phys, A-6020 Innsbruck, Austria..
    Heintzenberg, J.
    Leibniz Inst Tropospher Res, Leipzig, Germany..
    Held, A.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Univ Bayreuth, Bayreuth Ctr Ecol & Environm Res, Bayreuth, Germany..
    Hind, A.
    Bigelow Lab Ocean Sci, East Boothbay, ME USA..
    Johnston, P.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Div Phys Sci, Boulder, CO USA..
    Knulst, J.
    BNR Ecotour Consulting AB, Lammhult, Sweden..
    Martin, M.
    Swiss Fed Inst Technol, Inst Atmospher & Climate Sci, Zurich, Switzerland..
    Matrai, P. A.
    Bigelow Lab Ocean Sci, East Boothbay, ME USA..
    Mauritsen, T.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Max Planck Inst Meteorol, D-20146 Hamburg, Germany..
    Mueller, M.
    Univ Innsbruck, Inst Ion Phys & Appl Phys, A-6020 Innsbruck, Austria..
    Norris, S. J.
    Univ Leeds, Sch Earth & Environm, Inst Climate & Atmospher Sci, Leeds, W Yorkshire, England..
    Orellana, M. V.
    Inst Syst Biol, Seattle, WA USA..
    Orsini, D. A.
    Leibniz Inst Tropospher Res, Leipzig, Germany..
    Paatero, J.
    Finnish Meteorol Inst, FIN-00101 Helsinki, Finland..
    Persson, P. O. G.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Div Phys Sci, Boulder, CO USA..
    Gao, Q.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Rauschenberg, C.
    Bigelow Lab Ocean Sci, East Boothbay, ME USA..
    Ristovski, Z.
    Queensland Univ Technol, Sch Phys & Chem Sci, Brisbane, Qld 4001, Australia..
    Sedlar, J.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Swedish Meteorol & Hydrol Inst, S-60176 Norrkoping, Sweden..
    Shupe, M. D.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Div Phys Sci, Boulder, CO USA..
    Sierau, B.
    Swiss Fed Inst Technol, Inst Atmospher & Climate Sci, Zurich, Switzerland..
    Sirevaag, A.
    Univ Bergen, Inst Geophys, Bergen, Norway.;Bjerknes Ctr Climate Res, Bergen, Norway..
    Sjogren, S.
    Lund Univ, Div Nucl Phys, Lund, Sweden..
    Stetzer, O.
    Swiss Fed Inst Technol, Inst Atmospher & Climate Sci, Zurich, Switzerland..
    Swietlicki, E.
    Lund Univ, Div Nucl Phys, Lund, Sweden..
    Szczodrak, M.
    Univ Miami, Rosenstiel Sch Marine & Atmospher Sci, Miami, FL 33149 USA..
    Vaattovaara, P.
    Univ Eastern Finland, Dept Appl Phys, Kuopio, Finland..
    Wahlberg, N.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Westberg, M.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden..
    Wheeler, C. R.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA..
    The Arctic Summer Cloud Ocean Study (ASCOS): overview and experimental design2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 6, p. 2823-2869Article in journal (Refereed)
    Abstract [en]

    The climate in the Arctic is changing faster than anywhere else on earth. Poorly understood feedback processes relating to Arctic clouds and aerosol-cloud interactions contribute to a poor understanding of the present changes in the Arctic climate system, and also to a large spread in projections of future climate in the Arctic. The problem is exacerbated by the paucity of research-quality observations in the central Arctic. Improved formulations in climate models require such observations, which can only come from measurements in situ in this difficult-to-reach region with logistically demanding environmental conditions. The Arctic Summer Cloud Ocean Study (ASCOS) was the most extensive central Arctic Ocean expedition with an atmospheric focus during the International Polar Year (IPY) 2007-2008. ASCOS focused on the study of the formation and life cycle of low-level Arctic clouds. ASCOS departed from Longyearbyen on Svalbard on 2 August and returned on 9 September 2008. In transit into and out of the pack ice, four short research stations were undertaken in the Fram Strait: two in open water and two in the marginal ice zone. After traversing the pack ice northward, an ice camp was set up on 12 August at 87 degrees 21' N, 01 degrees 29' W and remained in operation through 1 September, drifting with the ice. During this time, extensive measurements were taken of atmospheric gas and particle chemistry and physics, mesoscale and boundary-layer meteorology, marine biology and chemistry, and upper ocean physics. ASCOS provides a unique interdisciplinary data set for development and testing of new hypotheses on cloud processes, their interactions with the sea ice and ocean and associated physical, chemical, and biological processes and interactions. For example, the first-ever quantitative observation of bubbles in Arctic leads, combined with the unique discovery of marine organic material, polymer gels with an origin in the ocean, inside cloud droplets suggests the possibility of primary marine organically derived cloud condensation nuclei in Arctic stratocumulus clouds. Direct observations of surface fluxes of aerosols could, however, not explain observed variability in aerosol concentrations, and the balance between local and remote aerosols sources remains open. Lack of cloud condensation nuclei (CCN) was at times a controlling factor in low-level cloud formation, and hence for the impact of clouds on the surface energy budget. ASCOS provided detailed measurements of the surface energy balance from late summer melt into the initial autumn freeze-up, and documented the effects of clouds and storms on the surface energy balance during this transition. In addition to such process-level studies, the unique, independent ASCOS data set can and is being used for validation of satellite retrievals, operational models, and reanalysis data sets.

  • 33. Treffeisen, R.
    et al.
    Krejci, R.
    Ström, J.
    Engvall, A. C.
    Herber, A.
    Thomason, L.
    Humidity observations in the Arctic troposphere over Ny-Alesund, Svalbard based on 15 years of radiosonde data2007In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 7, no 10, p. 2721-2732Article in journal (Refereed)
    Abstract [en]

    Water vapour is an important component in the radiative balance of the polar atmosphere. We present a study covering fifteen years of data of tropospheric humidity profiles measured with standard radiosondes at Ny-Alesund ( 78 degrees 55 0 N 11 degrees 52' E) during the period from 1991 to 2006. It is well-known that relative humidity measurements are less reliable at low temperatures when measured with standard radiosondes. The data was corrected for errors and used to determine key characteristic features of the vertical and temporal relative humidity evolution in the Arctic troposphere over Ny-Alesund. We present frequencies of occurrence of ice-supersaturation layers in the troposphere, their vertical span, temperature and statistical distribution. Supersaturation with respect to ice shows a clear seasonal behaviour. In winter, ( October - February) it occurred in 19% of all cases and less frequently in spring ( March - May 12%), and summer ( June - September, 9%). Finally, the results are compared with findings from the SAGE II satellite instrument on subvisible clouds.

  • 34. Treffeisen, R.
    et al.
    Tunved, P.
    Ström, J.
    Herber, A.
    Bareiss, J.
    Helbig, A.
    Stone, R. S.
    Hoyningen-Huene, W.
    Krejci, R.
    Stohl, A.
    Neuber, R.
    Arctic smoke - aerosol characteristics during a record smoke event in the European Arctic and its radiative impact2007In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 7, no 11, p. 3035-3053Article in journal (Refereed)
    Abstract [en]

    In early May 2006 a record high air pollution event was observed at Ny-Alesund, Spitsbergen. An atypical weather pattern established a pathway for the rapid transport of biomass burning aerosols from agricultural fires in Eastern Europe to the Arctic. Atmospheric stability was such that the smoke was constrained to low levels, within 2 km of the surface during the transport. A description of this smoke event in terms of transport and main aerosol characteristics can be found in Stohl et al. ( 2007). This study puts emphasis on the radiative effect of the smoke. The aerosol number size distribution was characterised by lognormal parameters as having an accumulation mode centered around 165-185 nm and almost 1.6 for geometric standard deviation of the mode. Nucleation and small Aitken mode particles were almost completely suppressed within the smoke plume measured at Ny-Alesund. Chemical and microphysical aerosol information obtained at Mt. Zeppelin (474 ma.s.l) was used to derive input parameters for a one-dimensional radiation transfer model to explore the radiative effects of the smoke. The daily mean heating rate calculated on 2 May 2006 for the average size distribution and measured chemical composition reached 0.55 K day(-1) at 0.5 km altitude for the assumed external mixture of the aerosols but showing much higher heating rates for an internal mixture (1.7 K day(-1)). In comparison a case study for March 2000 showed that the local climatic effects due to Arctic haze, using a regional climate model, HIRHAM, amounts to a maximum of 0.3 K day(-1) of heating at 2 km altitude (Treffeisen et al., 2005).

  • 35.
    Tunved, P.
    et al.
    Stockholm Univ, Dept Appl Environm Sci ITM, S-11418 Stockholm, Sweden..
    Ström, J.
    Stockholm Univ, Dept Appl Environm Sci ITM, S-11418 Stockholm, Sweden..
    Krejci, R.
    Stockholm Univ, Dept Appl Environm Sci ITM, S-11418 Stockholm, Sweden..
    Arctic aerosol life cycle: linking aerosol size distributions observed between 2000 and 2010 with air mass transport and precipitation at Zeppelin station, Ny-Alesund, Svalbard2013In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, no 7, p. 3643-3660Article in journal (Refereed)
    Abstract [en]

    In this study we present a qualitative and quantitative assessment of more than 10 yr of aerosol number size distribution data observed in the Arctic environment (Mt. Zeppelin (78 degrees 56' N, 11 degrees 53' E, 474 m a.s.l.), Ny Alesund, Svalbard). We provide statistics on both seasonal and diurnal characteristics of the aerosol observations and conclude that the Arctic aerosol number size distribution and related parameters such as integral mass and surface area exhibit a very pronounced seasonal variation. This seasonal variation seems to be controlled by both dominating source as well as meteorological conditions. Three distinctly different periods can be identified during the Arctic year: the haze period characterized by a dominating accumulation mode aerosol (March-May), followed by the sunlit summer period with low abundance of accumulation mode particles but high concentration of small particles which are likely to be recently and locally formed (June-August). The rest of the year is characterized by a comparably low concentration of accumulation mode particles and negligible abundance of ultrafine particles (September-February). A minimum in aerosol mass and number concentration is usually observed during September/October. We further show that the transition between the different regimes is fast, suggesting rapid change in the conditions defining their appearance. A source climatology based on trajectory analysis is provided, and it is shown that there is a strong seasonality of dominating source areas, with Eurasia dominating during the Autumn-Winter period and dominance of North Atlantic air during the summer months. We also show that new-particle formation events are rather common phenomena in the Arctic during summer, and this is the result of photochemical production of nucleating/condensing species in combination with low condensation sink. It is also suggested that wet removal may play a key role in defining the Arctic aerosol year, via the removal of accumulation mode size particles, which in turn have a pivotal role in facilitating the conditions favorable for new-particle formation events. In summary the aerosol Arctic year seems to be at least qualitatively predictable based on the knowledge of seasonality of transport paths and associated source areas, meteorological conditions and removal processes.

  • 36.
    Wesslen, C.
    et al.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Tjernström, M.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Bromwich, D. H.
    Ohio State Univ, Dept Geog, Atmospher Sci Program, Columbus, OH 43210 USA.;Ohio State Univ, Byrd Polar Res Ctr, Polar Meteorol Grp, Columbus, OH 43210 USA..
    de Boer, G.
    Univ Colorado, Cooperat Inst Res Environm Sci, Boulder, CO 80309 USA.;NOAA, Earth Syst Res Lab, Boulder, CO USA..
    Ekman, A. M. L.
    Stockholm Univ, Dept Meteorol, S-10691 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-10691 Stockholm, Sweden..
    Bai, L. -S
    Wang, S. -H
    The Arctic summer atmosphere: an evaluation of reanalyses using ASCOS data2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 5, p. 2605-2624Article in journal (Refereed)
    Abstract [en]

    The Arctic has experienced large climate changes over recent decades, the largest for any region on Earth. To understand the underlying reasons for this climate sensitivity, reanalysis is an invaluable tool. The Arctic System Reanalysis (ASR) is a regional reanalysis, forced by ERA-Interim at the lateral boundaries and incorporating model physics adapted to Arctic conditions, developed to serve as a state-of-the-art, high-resolution synthesis tool for assessing Arctic climate variability and monitoring Arctic climate change. We use data from Arctic Summer Cloud-Ocean Study (ASCOS) to evaluate the performance of ASR and ERAInterim for the Arctic Ocean. The ASCOS field experiment was deployed on the Swedish icebreaker Oden north of 87 degrees N in the Atlantic sector of the Arctic during August and early September 2008. Data were collected during the transits from and to Longyearbyen and the 3-week ice drift with Oden moored to a drifting multiyear ice floe. These data are independent and detailed enough to evaluate process descriptions. The reanalyses captures basic meteorological variations coupled to the synoptic-scale systems, but have difficulties in estimating clouds and atmospheric moisture. While ERAInterim has a systematic warm bias in the lowest troposphere, ASR has a cold bias of about the same magnitude on average. The results also indicate that more sophisticated descriptions of cloud microphysics in ASR did not significantly improve the modeling of cloud properties compared to ERA-Interim. This has consequences for the radiation balance, and hence the surface temperature, and illustrate how a modeling problem in one aspect of the atmosphere, here the clouds, feeds back to other parameters, especially near the surface and in the boundary layer.

  • 37.
    Yttri, K. E.
    et al.
    NILU Norwegian Inst Air Res, N-2027 Kjeller, Norway..
    Myhre, C. Lund
    NILU Norwegian Inst Air Res, N-2027 Kjeller, Norway..
    Eckhardt, S.
    NILU Norwegian Inst Air Res, N-2027 Kjeller, Norway..
    Fiebig, M.
    NILU Norwegian Inst Air Res, N-2027 Kjeller, Norway..
    Dye, C.
    NILU Norwegian Inst Air Res, N-2027 Kjeller, Norway..
    Hirdman, D.
    NILU Norwegian Inst Air Res, N-2027 Kjeller, Norway..
    Ström, J.
    Stockholm Univ, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    Klimont, Z.
    IIASA, A-2361 Laxenburg, Austria..
    Stohl, A.
    NILU Norwegian Inst Air Res, N-2027 Kjeller, Norway..
    Quantifying black carbon from biomass burning by means of levoglucosan - a one-year time series at the Arctic observatory Zeppelin2014In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 14, no 12, p. 6427-6442Article in journal (Refereed)
    Abstract [en]

    Levoglucosan, a highly specific tracer of particulate matter from biomass burning, has been used to study the influence of residential wood burning, agricultural waste burning and Boreal forest fire emissions on the Arctic atmosphere black carbon (BC) concentration. A one-year time series from March 2008 to March 2009 of levoglucosan has been established at the Zeppelin observatory in the European Arctic. Elevated concentrations of levoglucosan in winter (mean: 1.02 ng m(-3)) compared to summer (mean: 0.13 ng m(-3)) were observed, resembling the seasonal variation seen for e.g. sulfate and BC. The mean concentration in the winter period was 2-3 orders of magnitude lower than typical values reported for European urban areas in winter, and 1-2 orders of magnitude lower than European rural background concentrations. Episodes of elevated levoglucosan concentration lasting from 1 to 6 days were more frequent in winter than in summer and peak values were higher, exceeding 10 ng m(-3) at the most. Concentrations of elemental carbon from biomass burning (ECbb) were obtained by combining measured concentrations of levoglucosan and emission ratios of levoglucosan and EC for wildfires/agricultural fires and for residential wood burning. Neglecting chemical degradation by OH provides minimum levoglucosan concentrations, corresponding to a mean ECbb concentration of 3.7 +/- 1.2 ng m(-3) in winter (October-April) and 0.8 +/- 0.3 ng m(-3) in summer (May-September), or 8.8 +/- 4.5% of the measured equivalent black carbon (EBC) concentration in winter and 6.1 +/- 3.4% in summer. When accounting for chemical degradation of levoglucosan by OH, an upper estimate of 31-45% of EBC could be attributed to ECbb* (ECbb adjusted for chemical degradation) in winter, whereas no reliable (< 100%) upper estimate could be provided for summer for the degradation rates applied. Hence, fossil fuel sources appear to dominate the European Arctic BC concentrations in winter, whereas the very wide range obtained for summer does not allow us to conclude upon this for the warm season. Calculations using the Lagrangian particle dispersion model FLEXPART show that the seasonal variation of the modeled ECbb (ECbb,m) concentration compared relatively well with observationally derived ECbb from agricultural fires/wildfires during summer, and residential wood burning in winter. The model overestimates by a factor of 2.2 in winter and 4.4 in summer when compared to the observationally derived mean ECbb concentration, which provides the minimum estimate, whereas it underestimates by a factor of 2.3-3.3 in winter and a factor of 4.5 in summer when compared to ECbb*, which provides the upper estimate. There are indications of too-low emissions of residential wood burning in northern Russia, a region of great importance with respect to observed concentrations of BC in the European Arctic.

  • 38.
    Zabori, J.
    et al.
    Stockholm Univ, Dept Appl Environm Sci, S-11418 Stockholm, Sweden..
    Krejci, R.
    Stockholm Univ, Dept Appl Environm Sci, S-11418 Stockholm, Sweden.;Univ Helsinki, Dept Phys, Helsinki 00014, Finland..
    Ekman, A. M. L.
    Stockholm Univ, Dept Meteorol, S-11418 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-11418 Stockholm, Sweden..
    Mårtensson, E. M.
    Stockholm Univ, Dept Appl Environm Sci, S-11418 Stockholm, Sweden.;Uppsala Univ, Dept Earth Sci, S-75236 Uppsala, Sweden..
    Ström, J.
    Stockholm Univ, Dept Appl Environm Sci, S-11418 Stockholm, Sweden..
    de Leeuw, G.
    Finnish Meteorol Inst, Climate Change Unit, FIN-00101 Helsinki, Finland.;Univ Helsinki, Dept Phys, Helsinki 00014, Finland.;TNO B&O, NL-3508 TA Utrecht, Netherlands..
    Nilsson, E. D.
    Stockholm Univ, Dept Appl Environm Sci, S-11418 Stockholm, Sweden..
    Wintertime Arctic Ocean sea water properties and primary marine aerosol concentrations2012In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 12, no 21, p. 10405-10421Article in journal (Refereed)
    Abstract [en]

    Sea spray aerosols are an important part of the climate system through their direct and indirect effects. Due to the diminishing sea ice, the Arctic Ocean is one of the most rapidly changing sea spray aerosol source areas. However, the influence of these changes on primary particle production is not known. In laboratory experiments we examined the influence of Arctic Ocean water temperature, salinity, and oxygen saturation on primary particle concentration characteristics. Sea water temperature was identified as the most important of these parameters. A strong decrease in sea spray aerosol production with increasing water temperature was observed for water temperatures between -1 degrees C and 9 degrees C. Aerosol number concentrations decreased from at least 1400 cm(-3) to 350 cm-3. In general, the aerosol number size distribution exhibited a robust shape with one mode close to dry diameter D-p 0.2 mu m with approximately 45% of particles at smaller sizes. Changes in sea water temperature did not result in pronounced change of the shape of the aerosol size distribution, only in the magnitude of the concentrations. Our experiments indicate that changes in aerosol emissions are most likely linked to changes of the physical properties of sea water at low temperatures. The observed strong dependence of sea spray aerosol concentrations on sea water temperature, with a large fraction of the emitted particles in the typical cloud condensation nuclei size range, provide strong arguments for a more careful consideration of this effect in climate models.

  • 39.
    Zabori, J.
    et al.
    Stockholm Univ, Dept Appl Environm Sci, S-11418 Stockholm, Sweden..
    Krejci, R.
    Stockholm Univ, Dept Appl Environm Sci, S-11418 Stockholm, Sweden.;Univ Helsinki, Dept Phys, Helsinki 00014, Finland..
    Ström, J.
    Stockholm Univ, Dept Appl Environm Sci, S-11418 Stockholm, Sweden..
    Vaattovaara, P.
    Univ Eastern Finland, Dept Appl Phys, Kuopio 70211, Finland..
    Ekman, A. M. L.
    Stockholm Univ, Dept Meteorol, S-11418 Stockholm, Sweden.;Stockholm Univ, Bert Bolin Ctr Climate Res, S-11418 Stockholm, Sweden..
    Salter, M. E.
    Stockholm Univ, Dept Appl Environm Sci, S-11418 Stockholm, Sweden..
    Martensson, E. M.
    Stockholm Univ, Dept Appl Environm Sci, S-11418 Stockholm, Sweden.;Uppsala Univ, Dept Earth Sci, S-75236 Uppsala, Sweden..
    Nilsson, E. D.
    Stockholm Univ, Dept Appl Environm Sci, S-11418 Stockholm, Sweden..
    Comparison between summertime and wintertime Arctic Ocean primary marine aerosol properties2013In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, no 9, p. 4783-4799Article in journal (Refereed)
    Abstract [en]

    Primary marine aerosols (PMAs) are an important source of cloud condensation nuclei, and one of the key elements of the remote marine radiative budget. Changes occurring in the rapidly warming Arctic, most importantly the decreasing sea ice extent, will alter PMA production and hence the Arctic climate through a set of feedback processes. In light of this, laboratory experiments with Arctic Ocean water during both Arctic winter and summer were conducted and focused on PMA emissions as a function of season and water properties. Total particle number concentrations and particle number size distributions were used to characterize the PMA population. A comprehensive data set from the Arctic summer and winter showed a decrease in PMA concentrations for the covered water temperature (T-w) range between - 1 degrees C and 15 degrees C. A sharp decrease in PMA emissions for a T-w increase from -1 degrees C to 4 degrees C was followed by a lower rate of change in PMA emissions for T-w up to about 6 degrees C. Near constant number concentrations for water temperatures between 6 degrees C to 10 degrees C and higher were recorded. Even though the total particle number concentration changes for overlapping T-w ranges were consistent between the summer and winter measurements, the distribution of particle number concentrations among the different sizes varied between the seasons. Median particle number concentrations for a dry diameter (D-p) < 0.125 mu m measured during winter conditions were similar (deviation of up to 3 %), or lower (up to 70 %) than the ones measured during summer conditions (for the same water temperature range). For D-p > 0.125 mu m, the particle number concentrations during winter were mostly higher than in summer (up to 50 %). The normalized particle number size distribution as a function of water temperature was examined for both winter and summer measurements. An increase in T-w from -1 degrees C to 10 degrees C during winter measurements showed a decrease in the peak of relative particle number concentration at about a D-p of 0.180 mu m, while an increase was observed for particles with D-p > 1 mu m. Summer measurements exhibited a relative shift to smaller particle sizes for an increase of T-w in the range 7-11 degrees C. The differences in the shape of the number size distributions between winter and summer may be caused by different production of organic material in water, different local processes modifying the water masses within the fjord (for example sea ice production in winter and increased glacial meltwater inflow during summer) and different origin of the dominant sea water mass. Further research is needed regarding the contribution of these factors to the PMA production.

  • 40.
    Zieger, P.
    et al.
    Paul Scherrer Inst, Lab Atmospher Chem, CH-5232 Villigen, Switzerland..
    Fierz-Schmidhauser, R.
    Paul Scherrer Inst, Lab Atmospher Chem, CH-5232 Villigen, Switzerland..
    Gysel, M.
    Paul Scherrer Inst, Lab Atmospher Chem, CH-5232 Villigen, Switzerland..
    Ström, J.
    Norwegian Polar Res Inst, N-9296 Tromso, Norway..
    Henne, S.
    Empa, Lab Air Pollut & Environm Technol, CH-8600 Dubendorf, Switzerland..
    Yttri, K. E.
    Norwegian Inst Air Res, Dept Atmospher & Climate Res, N-2027 Kjeller, Norway..
    Baltensperger, U.
    Paul Scherrer Inst, Lab Atmospher Chem, CH-5232 Villigen, Switzerland..
    Weingartner, E.
    Paul Scherrer Inst, Lab Atmospher Chem, CH-5232 Villigen, Switzerland..
    Effects of relative humidity on aerosol light scattering in the Arctic2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 8, p. 3875-3890Article in journal (Refereed)
    Abstract [en]

    Aerosol particles experience hygroscopic growth in the ambient atmosphere. Their optical properties - especially the aerosol light scattering - are therefore strongly dependent on the ambient relative humidity (RH). In-situ light scattering measurements of long-term observations are usually performed under dry conditions (RH > 30-40%). The knowledge of this RH effect is of eminent importance for climate forcing calculations or for the comparison of remote sensing with in-situ measurements. This study combines measurements and model calculations to describe the RH effect on aerosol light scattering for the first time for aerosol particles present in summer and fall in the high Arctic. For this purpose, a field campaign was carried out from July to October 2008 at the Zeppelin station in Ny-Alesund, Svalbard. The aerosol light scattering coefficient Sigma(sp)(lambda) was measured at three distinct wavelengths (lambda=450, 550, and 700 nm) at dry and at various, predefined RH conditions between 20% and 95% with a recently developed humidified nephelometer (WetNeph) and with a second nephelometer measuring at dry conditions with an average RH < 10% (DryNeph). In addition, the aerosol size distribution and the aerosol absorption coefficient were measured. The scattering enhancement factor f(RH, lambda) is the key parameter to describe the RH effect on Sigma(sp)(lambda) and is defined as the RH dependent Sigma(sp)(RH, lambda) divided by the corresponding dry Sigma(sp)(RH(dry), lambda). During our campaign the average f(RH=85%, lambda=550 nm) was 3.24 +/- 0.63 (mean +/- standard deviation), and no clear wavelength dependence of f(RH, lambda) was observed. This means that the ambient scattering coefficients at RH=85% were on average about three times higher than the dry measured in-situ scattering coefficients. The RH dependency of the recorded f(RH, lambda) can be well described by an empirical one-parameter equation. We used a simplified method to retrieve an apparent hygroscopic growth factor g(RH), defined as the aerosol particle diameter at a certain RH divided by the dry diameter, using the WetNeph, the DryNeph, the aerosol size distribution measurements and Mie theory. With this approach we found, on average, g(RH)=85%) values to be 1.61 +/- 0.12 (mean +/- standard deviation). No clear seasonal shift of f(RH, lambda) was observed during the 3-month period, while aerosol properties (size and chemical composition) clearly changed with time. While the beginning of the campaign was mainly characterized by smaller and less hygroscopic particles, the end was dominated by larger and more hygroscopic particles. This suggests that compensating effects of hygroscopicity and size determined the temporal stability of f(RH, lambda). During sea salt influenced periods, distinct deliquescence transitions were observed. At the end we present a method on how to transfer the dry in-situ measured aerosol scattering coefficients to ambient values for the aerosol measured during summer and fall at this location.

  • 41. Ziska, F.
    et al.
    Quack, B.
    Abrahamsson, K.
    Archer, S. D.
    Atlas, E.
    Bell, T.
    Butler, J. H.
    Carpenter, L. J.
    Jones, C. E.
    Harris, N. R. P.
    Hepach, H.
    Heumann, K. G.
    Hughes, C.
    Kuss, J.
    Krueger, K.
    Liss, P.
    Moore, R. M.
    Orlikowska, A.
    Raimund, S.
    Reeves, C. E.
    Reifenhaeuser, W.
    Robinson, A. D.
    Schall, C.
    Tanhua, T.
    Tegtmeier, S.
    Turner, S.
    Wang, L.
    Wallace, D.
    Williams, J.
    Yamamoto, H.
    Yvon-Lewis, S.
    Yokouchi, Y.
    Global sea-to-air flux climatology for bromoform, dibromomethane and methyl iodide2013In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 13, no 17, p. 8915-8934Article in journal (Refereed)
    Abstract [en]

    Volatile halogenated organic compounds containing bromine and iodine, which are naturally produced in the ocean, are involved in ozone depletion in both the troposphere and stratosphere. Three prominent compounds transporting large amounts of marine halogens into the atmosphere are bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I). The input of marine halogens to the stratosphere has been estimated from observations and modelling studies using low-resolution oceanic emission scenarios derived from top-down approaches. In order to improve emission inventory estimates, we calculate data-based high resolution global sea-to-air flux estimates of these compounds from surface observations within the HalOcAt (Halocarbons in the Ocean and Atmosphere) database (https://halocat.geomar.de/). Global maps of marine and atmospheric surface concentrations are derived from the data which are divided into coastal, shelf and open ocean regions. Considering physical and biogeochemical characteristics of ocean and atmosphere, the open ocean water and atmosphere data are classified into 21 regions. The available data are interpolated onto a 1 degrees x 1 degrees grid while missing grid values are interpolated with latitudinal and longitudinal dependent regression techniques reflecting the compounds’ distributions. With the generated surface concentration climatologies for the ocean and atmosphere, global sea-to-air concentration gradients and sea-to-air fluxes are calculated. Based on these calculations we estimate a total global flux of 1.5/2.5 Gmol Br yr(-1) for CHBr3, 0.78/0.98 Gmol Br yr(-1) for CH2Br2 and 1.24/1.45 Gmol Br yr(-1) for CH3I (robust fit/ordinary least squares regression techniques). Contrary to recent studies, negative fluxes occur in each sea-to-air flux climatology, mainly in the Arctic and Antarctic regions. “Hot spots” for global polybromomethane emissions are located in the equatorial region, whereas methyl iodide emissions are enhanced in the subtropical gyre regions. Inter-annual and seasonal variation is contained within our flux calculations for all three compounds. Compared to earlier studies, our global fluxes are at the lower end of estimates, especially for bromoform. An under-representation of coastal emissions and of extreme events in our estimate might explain the mismatch between our bottom-up emission estimate and top-down approaches.

1 - 41 of 41
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf