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  • 1. Bigg, E. Keith
    et al.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology.
    The composition of fragments of bubbles bursting at the ocean surface2008In: Journal of geophysical research: Atmospheres, Vol. 113, no D11, p. D11209-Article in journal (Refereed)
    Abstract [en]

    Air bubbles bursting on artificial seawater in laboratory experiments have been found to inject numerous particles <200 nm diameter into the atmosphere, some experiments showing copious production of particles as small as 10 nm. Some observations of the real marine aerosol support the presence of a large proportion of sea salt <200 nm diameter, while others suggest that it is absent, or nearly so. It is argued here that the observations showing its presence may be misinterpretations. If this is so, modification of currently accepted theories of particle injection into the atmosphere by bursting bubbles would be required. Highly surface active exopolymers produced by bacteria and algae, the microgels formed by them, and large concentrations of submicrometer particulates are known to be present in the ocean. Their possible influence on bubble formation, bubble bursting and particle injection into the atmosphere are discussed. Electron microscopy of individual particles at a number of sites supports the proposal that the exopolymers are involved in these processes. Ultraviolet light and acidification cause structural and chemical changes to exopolymers and their gels exposed to the atmosphere so that marine aerosol will have properties that change with atmospheric residence time.

  • 2. Birch, C. E.
    et al.
    Brooks, I. M.
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Shupe, M. D.
    Mauritsen, T.
    Sedlar, J.
    Lock, A. P.
    Earnshaw, P.
    Persson, P. O. G.
    Milton, S. F.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    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, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    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)
    Abstract [en]

    Loss of summertime Arctic sea ice will lead to a large increase in the emission of aerosols and precursor gases from the ocean surface. It has been suggested that these enhanced emissions will exert substantial aerosol radiative forcings, dominated by the indirect effect of aerosol on clouds. Here, we investigate the potential for these indirect forcings using a global aerosol microphysics model evaluated against aerosol observations from the Arctic Summer Cloud Ocean Study (ASCOS) campaign to examine the response of Arctic cloud condensation nuclei (CCN) to sea-ice retreat. In response to a complete loss of summer ice, we find that north of 70 degrees N emission fluxes of sea salt, marine primary organic aerosol (OA) and dimethyl sulfide increase by a factor of similar to 10, similar to 4 and similar to 15 respectively. However, the CCN response is weak, with negative changes over the central Arctic Ocean. The weak response is due to the efficient scavenging of aerosol by extensive drizzling stratocumulus clouds. In the scavenging-dominated Arctic environment, the production of condensable vapour from oxidation of dimethyl sulfide grows particles to sizes where they can be scavenged. This loss is not sufficiently compensated by new particle formation, due to the suppression of nucleation by the large condensation sink resulting from sea-salt and primary OA emissions. Thus, our results suggest that increased aerosol emissions will not cause a climate feedback through changes in cloud microphysical and radiative properties.

  • 4. Budhavant, K. B.
    et al.
    Rao, P. S. P.
    Safai, P. D.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Rodhe, Henning
    Stockholm University, Faculty of Science, Department of Meteorology .
    Black carbon in cloud-water and rain water during monsoon season at a high altitude station in India2016In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 129, p. 256-264Article in journal (Refereed)
    Abstract [en]

    We present results of measurements of black carbon (BC) from ground-based wet-only rainwater (RW) and cloud-water (CW) sampling at a mountain field station, Sinhagad, situated in south western India during the period from June 2008 to October 2010. The amount of BC in the sample was determined by photometry at a wavelength of 528 nm after a procedure including the filtration through a 0.4 mu m polycarbonate membrane filter. Water soluble concentrations of major anions in RW and CW were also determined. The average concentration of BC in RW (16 mu mol dm(-3)) is higher by at least a factor 2 than that found in similar studies reported from other parts of the world. On the other hand, the average concentration of BC in CW (47 mu mol dm(-3)) is lower by about a factor of 2 than that found at other sites. The ratio between the average concentrations in CW and RW varies from 2 (K+) to 7 (SO42-). The ratio for BC was about 3. No significant difference was observed for pH. Analysis of air mass back trajectories and of correlations between the various components indicates that long range transport of pollutants and dust from East Africa and Southern part of the Arabian peninsula might contribute to the high concentrations of BC and some of the ionic constituents at Sinhagad during the monsoon season.

  • 5.
    Bulatovic, Ines
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Savre, J.
    Riipinen, Ilona
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Tampere University of Technology, Finland.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Aerosol Indirect Effects in Marine Stratocumulus: The Importance of Explicitly Predicting Cloud Droplet Activation2019In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 46, no 6, p. 3473-3481Article in journal (Refereed)
    Abstract [en]

    Climate models generally simulate a unidirectional, positive liquid water path (LWP) response to increasing aerosol number concentration. However, satellite observations and large-eddy simulations show that the LWP may either increase or decrease with increasing aerosol concentration, influencing the overall magnitude of the aerosol indirect effect (AIE). We use large-eddy simulation to investigate the LWP response of a marine stratocumulus cloud and its dependence on different parameterizations for obtaining cloud droplet number concentration (CDNC). The simulations confirm that the LWP response is not always positiveregardless of CDNC treatment. However, the AIE simulated with the model version with prescribed CDNC is almost 3 times larger compared to the version with prognostic CDNC. The reason is that the CDNC in the prognostic scheme varies in time due to supersaturation fluctuations, collection, and other microphysical processes. A substantial spread in simulated AIE may thus arise simply due to the CDNC treatment. Plain Language Summary Our poor understanding of aerosol-cloud-radiation interactions (aerosol indirect effects) results in a major uncertainty in estimates of anthropogenic aerosol forcing. In climate models, the cloud water response to an increased aerosol number concentration may be especially uncertain as models simplify, or do not account for, processes that affect the cloud droplet number concentration and the total amount of cloud water. In this study, we employ large-eddy simulation to explore how different model descriptions for obtaining the number concentration of cloud droplets influences the cloud water response of a marine stratocumulus cloud and thus the simulated aerosol indirect effect. Our simulations show a qualitatively similar cloud water response regardless of model description: the total amount of cloud water increases first and then decreases with increasing aerosol concentration. However, the simulated aerosol indirect effect is almost 3 times as large when the number concentration of cloud droplets is prescribed compared to when it is dependent on the calculated supersaturation and other microphysical processes such as collisions between cloud droplets. Our findings show that a relatively simple difference in the treatment of the number concentration of cloud droplets in climate models may result in a significant spread in the simulated aerosol indirect effect.

  • 6. Chang, R. Y. -W
    et al.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Graus, M.
    Mueller, M.
    Paatero, J.
    Burkhart, J. F.
    Stohl, A.
    Orr, L. H.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hayden, K.
    Li, S. -M
    Hansel, A.
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leaitch, W. R.
    Abbatt, J. P. D.
    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.

  • 7.
    Coz Diego, Esther
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Morphology and state of mixture of atmospheric soot aggregates during the winter season over Southern Asia-a quantitative approach2011In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 63, no 1, p. 107-116Article in journal (Refereed)
    Abstract [en]

    The atmospheric brown cloud phenomena characterized by a high content of soot and a large impact on the solar radiative heating especially affects the tropical Indian Ocean during the winter season. The present study focuses on morphological characteristics and state of mixture of soot aggregates during the winter season over India. Given are quantitative measures of size, morphology and texture on aggregates collected in air at two different sites: Sinhagad near Pune in India and Hanimaadhoo in Maldives. For the latter site two different synoptic patterns prevailed: advection of air from the Arabian region and from the Indian subcontinent, respectively. Aggregates collected at Sinhagad, were associated with open branched structures, characteristic of fresh emission and diameters between 220 and 460 nm. The Hanimaadhoo aggregates were associated with aged closed structures, smaller sizes (130-360 nm) and frequently contained inorganic inclusions. Those arriving from the Indian subcontinent were characterized by the presence of an additional organic layer that covered the aggregate structure. These organic coatings might be a reasonable explanation of the low average wash-out ratios of soot two to seven times lower than that of nss-SO(4)2- that have been reported for air flow arriving at Hanimaadhoo from the Indian subcontinent in winter.

  • 8.
    Das, Ruby
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Granat, Lennart
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Praveen, P. S.
    Rodhe, Henning
    Stockholm University, Faculty of Science, Department of Meteorology .
    Chemical composition of rainwater at Maldives Climate Observatory at Hanimaadhoo (MCOH)2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 8, p. 3743-3755Article in journal (Refereed)
    Abstract [en]

    Water-soluble inorganic components in rain deposited at the Maldives Climate Observatory Hanimaadhoo (MCOH) were examined to determine seasonality and possible source regions. The study, which is part of the Atmospheric Brown Cloud (ABC) project, covers the period June 2005 to December 2007. Air mass trajectories were used to separate the data into situations with transport of air from India and adjacent parts of the Asian continent during the months December and January (Indian group) and those with southerly flow from the Indian Ocean during the summer monsoon season June to September (Marine group). A third trajectory group was identified with transport from the northern parts of the Arabian Sea and adjacent land areas during the months March, April and October (Arabian Sea group). The concentrations of nss-SO(4)(2-), NH(4)(+) and NO(3)(-) were more than a factor of 4 higher in the Indian group than in the Marine group. The average rainwater pH was significantly lower in the Indian group (4.7) than in the Marine group (6.0). This shows a pronounced influence of continental pollutants during December and January. The origin of the very high concentration of nss-Ca(2+) found in the Marine group - a factor of 7 higher than in the Indian group - is unclear. We discuss various possibilities including long-range transport from the African or Australian continents, local dust from nearby islands and calcareous plankton debris and exopolymer gels emitted from the ocean surface. The occurrence of NO(3)(-) and NH(4)(+) in the Marine group suggests emissions from the ocean surface. Part of the NO(3)(-) could also be associated with lightning over the ocean. Despite the fact that the concentrations of nss-SO(4)(2-), NO(3)(-), and NH(4)(+) were highest in the Indian group the wet deposition was at least as big in the Marine group reflecting the larger amount of rainfall during the monsoon season. The annual wet deposition of NO(3)(-), NH(4)(+) and nss-SO(4)(2-) at MCOH is about a factor of three lower than observed at rural sites in India.

  • 9.
    Engström, Erik J.
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Reducing uncertainties associated with filter-based optical measurements of soot aerosol particles with chemical information.In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324Article in journal (Refereed)
    Abstract [en]

    Of the many identified and potential effects ofatmospheric aerosol particles on climate, those of soot particlesare the most uncertain, in that analytical techniques concerningsoot are far from satisfactory. One concern whenapplying filter-based optical measurements of soot is thatthey suffer from systematic errors due to the light scatteringof non-absorbing particles co-deposited on the filter, suchas inorganic salts and mineral dust. In addition to an opticalcorrection of the non-absorbing material this study providesa protocol for correction of light scattering based onthe chemical quantification of the material, which is a novelty.A newly designed Particle Soot Absorption Photometerwas constructed to measure light transmission on particleaccumulating filters, which includes an additional sensorrecording backscattered light. The choice of polycarbonatemembrane filters avoided high chemical blank values and reducederrors associated with length of the light path throughthe filter.Two protocols of corrections were applied to aerosol samplescollected at the Maldives Climate Observatory Hanimaadhooduring episodes with either continentally influencedair from the Indian/Arabian subcontinents (wintermonsoon) or pristine air from the Southern Indian Ocean(summer monsoon). The two ways of correction (optical andchemical) lowered the particle light absorption of soot by 63 to 61 %, respectively, for data from the Arabian Sea sourcedgroup, resulting in median soot absorption coefficients of 4.2 and 3.5 Mm-1. Corresponding values for the South IndianOcean data were 69 and 97 % (0.38 and 0.02 Mm-1). A comparison with other studies in the area indicated anoverestimation of their soot levels, by up to two orders ofmagnitude. This raises the necessity for chemical correctionprotocols on optical filter-based determinations of soot, before even the sign on the radiative forcing based on their effectscan be assessed.

  • 10.
    Engström, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Determination of water-insoluble light absorbing matter in rainwater using polycarbonate membrane lters and photometricdetection.Article in journal (Refereed)
  • 11.
    Engström, J. E.
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Reducing uncertainties associated with filter-based optical measurements of light absorbing carbon particles with chemical information2011In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 4, no 8, p. 1553-1566Article in journal (Refereed)
    Abstract [en]

    The presented filter-based optical method for determination of soot (light absorbing carbon or Black Carbon, BC) can be implemented in the field under primitive conditions and at low cost. This enables researchers with small economical means to perform monitoring at remote locations, especially in the Asia where it is much needed. One concern when applying filter-based optical measurements of BC is that they suffer from systematic errors due to the light scattering of non-absorbing particles co-deposited on the filter, such as inorganic salts and mineral dust. In addition to an optical correction of the non-absorbing material this study provides a protocol for correction of light scattering based on the chemical quantification of the material, which is a novelty. A newly designed photometer was implemented to measure light transmission on particle accumulating filters, which includes an additional sensor recording backscattered light. The choice of polycarbonate membrane filters avoided high chemical blank values and reduced errors associated with length of the light path through the filter. Two protocols for corrections were applied to aerosol samples collected at the Maldives Climate Observatory Hanimaadhoo during episodes with either continentally influenced air from the Indian/Arabian subcontinents (winter season) or pristine air from the Southern Indian Ocean (summer monsoon). The two ways of correction (optical and chemical) lowered the particle light absorption of BC by 63 to 61 %, respectively, for data from the Arabian Sea sourced group, resulting in median BC absorption coefficients of 4.2 and 3.5 Mm(-1). Corresponding values for the South Indian Ocean data were 69 and 97% (0.38 and 0.02 Mm(-1)). A comparison with other studies in the area indicated an overestimation of their BC levels, by up to two orders of magnitude. This raises the necessity for chemical correction protocols on optical filter-based determinations of BC, before even the sign on the radiative forcing based on their effects can be assessed.

  • 12.
    Engström, J. Erik
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Seasonal variability in atmospheric black carbon at three stations in South-Asia2017In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 69, article id 1331102Article in journal (Refereed)
    Abstract [en]

    Filter-based optical measurements of black carbon in air, a constituent of soot, have been determined with a 528 nm light source during the period from 1 June 2005 to 31 May 2009 on samples taken at Godavari in Nepal, Sinhagad in India and Hanimaadhoo in the Maldives. In order to reduce systematic errors due to the light scattering of non-absorbing particles co-deposited on the filter, such as inorganic salts and mineral dust, an additional sensor recording backscattered light was implemented. Two protocols of corrections (optical and chemical) were applied to the samples collected at the observatories. The Indian monsoon circulation with its two annual phases in combination with the location of the combustion sources and their contribution relative to other non-anthropogenic sources dominated the observed patterns of black carbon at two of the observatories: in India and the Maldives. The observatory in Nepal was however mainly influenced by combustion sources all year around concealing possible variability related to the monsoon circulation. At the receptor observatory in the Maldives, peak values in the black carbon absorption coefficient occurred during the winter season (December to April) when air was transported from the polluted Indian subcontinent out over the Indian Ocean. A close to two orders of magnitude lower values were recorded in air that had spent more than 10-days over the Indian Ocean during the monsoon season (July to September), suggested to be dominated by particulate matter from remote marine biogenic sources and not by combustion sources.

  • 13.
    Franke, Vera
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Swedish University of Agricultural Sciences, Sweden.
    Zieger, Paul
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Wideqvist, Ulla
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Acosta Navarro, Juan Camilo
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Barcelona Supercomputing Center, Spain.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Rosati, Bernadette
    Gysel, Martin
    Salter, Matthew Edward
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Chemical composition and source analysis of carbonaceous aerosol particles at a mountaintop site in central Sweden2017In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 69, article id 1353387Article in journal (Refereed)
    Abstract [en]

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

  • 14.
    Gao, Qiuju
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Araia, Musie
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Emmer, Åsa
    Characterization of exopolysaccharides in marine colloids by capillary electrophoresis with indirect UV detection2010In: Analytica Chimica Acta, ISSN 0003-2670, E-ISSN 1873-4324, Vol. 662, no 2, p. 193-199Article in journal (Refereed)
    Abstract [en]

    A method was established using capillary electrophoresis with indirect UV detection for analysis of monosaccharides liberated from exopolysaccharides by acidic hydrolysis. Tangential flow filtration was used to isolate high molecular weight polysaccharides from seawater. The capillary electrophoresis method included the use of a background electrolyte consisting of 2,6-dimethoxyphenol and cetyltrimethylammonium bromide. Several neutral sugars commonly existing in marine polysaccharides were separated under optimized conditions. The relative standard deviations were between 1.3% and 2.3% for relative migration time and 1.3-2.5% for peak height. Detection limits (at S/N 3) were in the range of 27.2-47.8 mu M. The proposed approach was applied to the analysis of hydrolyzed colloidal polysaccharides in seawater collected from the Baltic Sea. Nanomolar levels of liberated monosaccharides in seawater samples can be detected by preconcentration up to 30,000 times.

  • 15.
    Gao, Qiuju
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Rauschenberg, Carlton
    Matrai, Patricia A.
    On the chemical dynamics of extracellular polysaccharides in the high Arctic surface microlayer2012In: Ocean Science, ISSN 1812-0784, E-ISSN 1812-0792, Vol. 8, no 4, p. 401-418Article in journal (Refereed)
    Abstract [en]

    The surface microlayer (SML) represents a unique system of which the physicochemical characteristics may differ from those of the underlying subsurface seawater (SSW). Within the Arctic pack ice area, the SML has been characterized as enriched in small colloids of biological origin, resulting from extracellular polymeric secretions (EPS). During the Arctic Summer Cloud-Ocean Study (ASCOS) in August 2008, particulate and dissolved organic matter (POM, DOM) samples were collected and chemically characterized from the SML and the corresponding SSW at an open lead centered at 87.5° N and 5°E.  Total organic carbon was persistently enriched in the SML with a mean enrichment factor (EF) of 1.45 ± 0.41, whereas sporadic depletions of dissolved carbohydrates and amino acids were observed. Monosaccharide compositional analysis reveals that EPS in the Arctic lead was formed mainly of distinctive heteropolysaccharides, enriched in xylose, fucose and glucose. The mean concentrations of total hydrolysable neutral sugars in SSW were 94.9 ± 37.5 nM in high molecular weight (HMW) DOM and 64.4 ± 14.5 nM in POM. The enrichment of polysaccharides in the SML appeared to be a common feature, with EFs ranging from 1.7 to 7.0 for particulate polysaccharides and 3.5 to 12.1 for polysaccharides in the HMW DOM fraction. A calculated monosaccharide yield suggests that polymers in the HMW DOM fraction were scavenged, without substantial degradation, into the SML.  Bubble scavenging experiments showed that newly aggregated particles could be formed abiotically by coagulation of low molecular weight nanometer-sized gels. Experimentally-generated aerosol particles were enriched in polysaccharides by factors of 22-70, relative to the source seawater. We propose that bubble scavenging of surface-active polysaccharides was one of the possible mechanisms for the enrichment of polysaccharides in the SML.

  • 16.
    Gao, Qiuju
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Ulrika
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Ilag, Leopold L.
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Monosaccharide compositional analysis of marine polysaccharides by hydrophilic interaction liquid chromatography-tandem mass spectrometry2011In: Analytical and Bioanalytical Chemistry, ISSN 1618-2642, E-ISSN 1618-2650, Vol. 399, no 7, p. 2517-2529Article in journal (Refereed)
    Abstract [en]

    A simple and sensitive method was developed using hydrophilic interaction liquid chromatography coupled to tandem mass spectrometry for determination of monosaccharides liberated from marine polysaccharides by acidic hydrolysis. Optimal separation of diastereomeric monosaccharides including hexoses, pentoses, and deoxyhexoses was achieved using an aminopropyl bonded column with mobile phase containing ternary solvents (acetonitrile/methanol/water) in conjunction with MS/MS in SRM mode. Mechanisms for fragmentation of deprotonated monosaccharides with regard to cross-ring cleavage were proposed. Matrix effects from coeluting interferences were observed and isotopic-labeled internal standard was used to compensate for the signal suppression. The method demonstrated excellent instrumental limits of detection (LOD), ranging from 0.7 to 4.2 pg. Method LODs range from 0.9 to 5.1 nM. The proposed method was applied to the analysis of polysaccharides in seawater collected from the open leads of the central Arctic Ocean in the summer of 2008.

  • 17.
    Gustafsson, Örjan
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Kruså, Martin
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Zencak, Zdenek
    Sheesley, Rebecca J.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Granat, Lennart
    Stockholm University, Faculty of Science, Department of Meteorology .
    Engström, Erik
    Stockholm University, Faculty of Science, Department of Meteorology .
    Praveen, P.S.
    Rao, P.S.P.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Rodhe, Henning
    Stockholm University, Faculty of Science, Department of Meteorology .
    Brown clouds over South Asia: Biomass or fossil fuel combustion?2009In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 323, no 23 January, p. 495-498Article in journal (Refereed)
  • 18.
    Hamacher-Barth, Evelyne
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    A method for sizing submicrometer particles in air collected on Formvar films and imaged by scanning electron microscopy2013In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 6, no 12, p. 3459-3475Article in journal (Refereed)
    Abstract [en]

    A method was developed to systematically investigate individual aerosol particles collected onto a polyvinyl formal (Formvar)-coated copper grid with scanning electron microscopy. At very mild conditions with a low accelerating voltage of 2 kV and Gentle Beam mode aerosol particles down to 20 nm in diameter can be observed. Subsequent processing of the images with digital image analysis provides size resolved and morphological information (elongation, circularity) on the aerosol particle population. Polystyrene nanospheres in the expected size range of the ambient aerosol particles (20–900 nm in diameter) were used to confirm the accuracy of sizing and determination of morphological parameters. The relative standard deviation of the diameters of the spheres was better than ±10% for sizes larger than 40 nm and ±18% for 21 nm particles compared to the manufacturer's certificate. Atmospheric particles were collected during an icebreaker expedition to the high Arctic (north of 80°) in the summer of 2008. Two samples collected during two different meteorological regimes were analyzed. Their size distributions were compared with simultaneously collected size distributions from a Twin Differential Mobility Particle Sizer, which confirmed that a representative fraction of the aerosol particles was imaged under the electron microscope. The size distributions obtained by scanning electron microscopy showed good agreement with the Twin Differential Mobility Sizer in the Aitken mode, whereas in the accumulation mode the size determination was critically dependent on the contrast of the aerosol with the Formvar-coated copper grid. The morphological properties (elongation, circularity) changed with the number of days the air masses spent over the pack-ice area north of 80° before the aerosol particles were collected at the position of the icebreaker and are thus an appropriate measure to characterize transformation processes of ambient aerosol particles.

  • 19.
    Hamacher-Barth, Evelyne
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    The evolution of the high Arctic summer aerosol over the pack iceManuscript (preprint) (Other academic)
    Abstract [en]

    Ambient aerosol samples were collected over the pack ice north of 80° N during the summer of 2008 during the course of the ASCOS campaign. Aerosol particles were collected during nine sampling events and were subsequently sorted into five groups according to the number of days the air spent over the pack ice since last contact with the ice edge. As a tracer for marine sources, the molar ratio of methane sulfonic acid/non-sea-salt-sulfate was used. Scanning electron microscopy allowed size resolved identification of three types of aerosol particles, single particles, gel particles and halo particles within each sample group. Between the five groups we found significant differences in aerosol morphology, largely dependent on the time of advection over the pack ice (days over ice, DOI) and the synoptic weather encountered. The most obvious differences were observed for marine gel particles. The fraction of these particles in the lower accumulation mode, ≤ 100 nm, increased from 15% (DOI = 1) over 20% (DOI = 3.2) and 27% (DOI= 6.7) to 30% (DOI = 8.9). In parallel the gel particle morphology changed with increasing DOI value, from a widely outspread and weakly contrasting morphology (DOI = 1) over a more distinct and better contrasting appearance (DOI = 3.2) to sharply and well contoured particles (DOI = 6.7). The gel particles with the highest DOI value (DOI = 8.9), however, showed a branched and widely outspread morphology that indicated a relatively recent emission of these particles into the submicrometer size range, either from sources over the pack ice or through fragmentation of supermicrometer particles.

  • 20.
    Hamacher-Barth, Evelyne
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Size-resolved morphological properties of the high Arctic summer aerosol during ASCOS-20082016In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 16, no 10, p. 6577-6593Article in journal (Refereed)
    Abstract [en]

    The representation of aerosol properties and processes in climate models is fraught with large uncertainties. Especially at high northern latitudes a strong underprediction of aerosol concentrations and nucleation events is observed and can only be constrained by in situ observations based on the analysis of individual aerosol particles. To further reduce the uncertainties surrounding aerosol properties and their potential role as cloud condensation nuclei this study provides observational data resolved over size on morphological and chemical properties of aerosol particles collected in the summer high Arctic, north of 80A degrees aEuro-N. Aerosol particles were imaged with scanning and transmission electron microscopy and further evaluated with digital image analysis. In total, 3909 aerosol particles were imaged and categorized according to morphological similarities into three gross morphological groups: single particles, gel particles, and halo particles. Single particles were observed between 15 and 800aEuro-nm in diameter and represent the dominating type of particles (82aEuro-%). The majority of particles appeared to be marine gels with a broad Aitken mode peaking at 70aEuro-nm and accompanied by a minor fraction of ammonium (bi)sulfate with a maximum at 170aEuro-nm in number concentration. Gel particles (11aEuro-% of all particles) were observed between 45 and 800aEuro-nm with a maximum at 154aEuro-nm in diameter. Imaging with transmission electron microscopy allowed further morphological discrimination of gel particles in 'aggregate' particles, 'aggregate with film' particles, and 'mucus-like' particles. Halo particles were observed above 75aEuro-nm and appeared to be ammonium (bi)sulfate (59aEuro-% of halo particles), gel matter (19aEuro-%), or decomposed gel matter (22aEuro-%), which were internally mixed with sulfuric acid, methane sulfonic acid, or ammonium (bi)sulfate with a maximum at 161aEuro-nm in diameter. Elemental dispersive X-ray spectroscopy analysis of individual particles revealed a prevalence of the monovalent ions Na+/K+ for single particles and aggregate particles and of the divalent ions Ca2+/Mg2+ for aggregate with film particles and mucus-like particles. According to these results and other model studies, we propose a relationship between the availability of Na+/K+ and Ca2+/Mg2+ and the length of the biopolymer molecules participating in the formation of the three-dimensional gel networks.

  • 21.
    Hede, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Sun, Lu
    Royal Inst Technol, Sch Biotechnol, Dept Theoret Chem, S-10691 Stockholm, Sweden.
    Tu, Yaoquan
    Royal Inst Technol, Sch Biotechnol, Dept Theoret Chem, S-10691 Stockholm, Sweden.
    Ågren, Hans
    Royal Inst Technol, Sch Biotechnol, Dept Theoret Chem, S-10691 Stockholm, Sweden.
    A theoretical study revealing the promotion of light absorbing carbon particles solubilization by natural surfactants in nanosized water droplets2013In: Atmospheric Science Letters, ISSN 1530-261X, E-ISSN 1530-261X, Vol. 14, no 2, p. 86-90Article in journal (Refereed)
    Abstract [en]

    Many identified effects of atmospheric aerosol particles on climate come from pollutants. The effects of light absorbing carbon particles (soot) are amongst the most uncertain and they are also considered to cause climate warming on the same order of magnitude as anthropogenic carbon dioxide. This study contributes to the understanding of the potential for transformation of the surface character of soot from hydrophobic to hydrophilic, which in clouds promotes a buil-up of water-soluble material. We use molecular dynamics simulations to show how natural surfactants facilitate solubilization of fluoranthene, which we use as a model compound for soot, in nanoaerosol water clusters.

  • 22.
    Hede, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Li, Xin
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tu, Yaoquan
    Ågren, Hans
    Model HULIS compounds in nanoaerosol clusters - investigations of surface tension and aggregate formation using molecular dynamics simulations2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 13, p. 6549-6557Article in journal (Refereed)
    Abstract [en]

    Cloud condensation nuclei act as cores for water vapour condensation, and their composition and chemical properties may enhance or depress the ability for droplet growth. In this study we use molecular dynamics simulations to show that model humic-like substances (HULIS) in systems containing 10 000 water molecules mimic experimental data well referring to reduction of surface tension. The model HULIS compounds investigated in this study are cis-pinonic acid (CPA), pinic acid (PAD) and pinonaldehyde (PAL). The structural properties examined show the ability for the model HULIS compounds to aggregate inside the nanoaerosol clusters.

  • 23.
    Hede, Thomas
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Murugan, N. Arul
    Kongsted, Jacob
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ågren, Hans
    Simulations of Light Absorption of Carbon Particles in Nanoaerosol Clusters2014In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 118, no 10, p. 1879-1886Article in journal (Refereed)
    Abstract [en]

    Black carbon soot (BS) is considered to be the second most contributing organic matter next to carbon dioxide for the global warming effect. There is, however, so far no consensus on the quantitative warming effect due to the increased distribution of black carbon in the atmosphere. A recent report (Science 2012, 337, 1078) suggests that due to BS there is only a few percentage enhancement in absorption of BS-immersed aerosols. To get proper interpretation of the available experimental data, it becomes essential to obtain details of the microscopic origin of the absorption and scattering processes of the aerosol clusters due to the presence of soot. However, so far, due to the large spatial scale and the need for a quantum mechanical description of the particles involved in the absorption and scattering, this quest has posed an insurmountable challenge. In the present work we propose the use of a multiscale integrated approach based on molecular dynamics and a quantum mechanical molecular mechanical method to model the optical property of molecules immersed in nanosized aerosol particles. We choose fluoranthene (FA) with varying cis-pinonic acid (CPA) impurity concentration as an illustrative example of application. We observe that normally FA tends to be on the surface of the nanoaerosols but in the presence of CPA impurities its spatial location changes to a core aggregate to some extent. We find that the absorption maximum is only slightly red-shifted in the presence of increased CPA concentrations and that the oscillator strengths are not altered significantly. The comparable values for the oscillator strengths of all the low energy excitations suggest that the absorption enhancement of the aerosol due to BS will not be substantial, which is in line with the recent experimental report in Science.

  • 24. Heintzenberg, J.
    et al.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    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 80A degrees, 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.

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

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

  • 26. Heintzenberg, Jost
    et al.
    Cereceda-Balic, Francisco
    Vidal, Victor
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Scavenging of black carbon in Chilean coastal fogs2016In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 541, p. 341-347Article in journal (Refereed)
    Abstract [en]

    In November/December 2013 a pilot experiment on aerosol/fog interaction was conducted on a coastal hill in the suburbs of Valparaiso, Chile. Passages of garua fog were monitored with continuous recordings of a soot photometer and an optical aerosol spectrometer. An optical fog sensor and an automatic weather station provided meteorological data with which the aerosol could be classified. High-resolution back trajectories added meteorological information. From filter samples, optical and chemical aerosol information was derived. Scavenging coefficients of black carbon (BC) and measured particulate mass below 1 mu m diameter (PM1) were estimated with three approaches. Averaging over all fog periods of the campaign yielded a scavenging coefficient of only 6% for BC and 40% for PM1. Dividing the data into four 90 degrees-wind sectors gave scavenging factors for BC ranging from 13% over the Valparaiso, Vina del Mar conurbation to 50% in the marine sector (180 degrees-270 degrees). The third, and independent approach was achieved with two pairs of chemical aerosol samples taken inside and outside fogs, which yielded a scavenging coefficient of 25% for BC and 70% for nonseasalt sulfate. Whereas fogs occurred rather infrequently in the beginning of the campaign highly regular daily fog cycles appeared towards the end of the experiment, which allowed the calculation of typical diurnal cycles of the aerosol in relation to a fog passage.

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

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

  • 28.
    Held, A.
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Brooks, I. M.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tjernström, M.
    Stockholm University, Faculty of Science, Department of Meteorology .
    On the potential contribution of open lead particle emissions to the = ntral 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.

  • 29. Held, A.
    et al.
    Orsini, D. A.
    Vaattovaara, P.
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Near-surface profiles of aerosol number concentration and temperature over the Arctic Ocean2011In: Atmospheric Measurement Techniques, ISSN 1867-1381, Vol. 4, no 8, p. 1603-1616Article in journal (Refereed)
    Abstract [en]

    Temperature and particle number concentration profiles were measured at small height intervals above open and frozen leads and snow surfaces in the central Arctic. The device used was a gradient pole designed to investigate potential particle sources over the central Arctic Ocean. The collected data were fitted according to basic logarithmic flux-profile relationships to calculate the sensible heat flux and particle deposition velocity. Independent measurements by the eddy covariance technique were conducted at the same location. General agreement was observed between the two methods when logarithmic profiles could be fitted to the gradient pole data. In general, snow surfaces behaved as weak particle sinks with a maximum deposition velocity upsilon(d) = 1.3 mm s(-1) measured with the gradient pole. The lead surface behaved as a weak particle source before freeze-up with an upward flux F(c) = 5.7 x 10(4) particles m(-2) s(-1), and as a relatively strong heat source after freeze-up, with an upward maximum sensible heat flux H = 13.1 W m(-2). Over the frozen lead, however, we were unable to resolve any significant aerosol profiles.

  • 30. Hellen, Heidi
    et al.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Paatero, Jussi
    Virkkula, Aki
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hakola, Hannele
    Summer concentrations of NMHCs in ambient air of the Arctic and Antarctic2012In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 17, no 5, p. 385-397Article in journal (Refereed)
    Abstract [en]

    Summer concentrations of C-2-C-6 non-methane hydrocarbons (NMHCs) were measured in Antarctica and in the Arctic in 2008. The results show that NMHC concentrations are on average five times higher in the Arctic than in Antarctica. In Antarctica, there were few concentration peaks, but during most of the remaining time concentrations were below or close to the detection limits. Over the Arctic pack ice area north of 80 degrees, concentrations of most of the measured NMHCs were always above the detection limits. No differences based on air-mass origin were detected in Antarctica, but samples collected over the central Arctic Ocean showed higher concentrations in air masses being advected from the Kara Sea and the western-central Arctic Ocean. The relatively higher NMHC-to-ethyne molar ratios calculated for samples collected over the central Arctic Ocean suggest additional alkane sources in the region.

  • 31.
    Höpner, Friederike
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Bender, Frida A.-M.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Investigation of Two Optical Methods for Aerosol‐Type Classification Extended to a Northern Indian Ocean Site2019In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 124, no 15, p. 8743-8763Article in journal (Refereed)
    Abstract [en]

    Methods for determining aerosol types in cases where chemical composition measurements are not available are useful for improved aerosol radiative forcing estimates. In this study, two aerosol characterization methods by Cazorla et al. (2013, https://doi.org/10.5194/acp-13-9337-2013; CA13) and Costabile et al. (2013, https://doi.org/10.5194/acp-13-2455-2013; CO13) using wavelength‐dependent particle absorption and scattering are used, to assess their applicability and examine their limitations. Long‐term ambient particle optical property and chemical composition (major inorganic ions and bulk carbon) measurements from the Maldives Climate Observatory Hanimaadhoo as well as concurrent air mass trajectories are utilized to test the classifications based on the determined absorption Ångström exponent, scattering Ångström exponent, and single scattering albedo. The resulting aerosol types from the CA13 method show a good qualitative agreement with the particle chemical composition and air mass origin. In general, the size differentiation using the scattering Ångström exponent works very well for both methods, while the composition identification depending mainly on the absorption Ångström exponent can result in aerosol misclassifications at Maldives Climate Observatory Hanimaadhoo. To broaden the applicability of the CA13 method, we suggest to include an underlying marine aerosol group in the classification scheme. The classification of the CO13 method is less clear, and its applicability is limited when it is extended to aerosols in this environment at ambient humidity.

  • 32.
    Höpner, Friederike
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Beres, Nicholas
    Bender, Frida
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Comparison of BC measurement methods at a marine receptor siteManuscript (preprint) (Other academic)
  • 33. Igel, Adele L.
    et al.
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Savre, Julien
    Sedlar, Joseph
    Stockholm University, Faculty of Science, Department of Meteorology .
    The free troposphere as a potential source of arctic boundary layer aerosol particles2017In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 13, p. 7053-7060Article in journal (Refereed)
    Abstract [en]

    This study investigates aerosol particle transport from the free troposphere to the boundary layer in the summertime high Arctic. Observations from the Arctic Summer Cloud Ocean Study field campaign show several occurrences of high aerosol particle concentrations above the boundary layer top. Large-eddy simulations suggest that when these enhanced aerosol concentrations are present, they can be an important source of aerosol particles for the boundary layer. Most particles are transported to the boundary layer by entrainment. However, it is found that mixed-phase stratocumulus clouds, which often extend into the inversion layer, also can mediate the transport of particles into the boundary layer by activation at cloud top and evaporation below cloud base. Finally, the simulations also suggest that aerosol properties at the surface sometimes may not be good indicators of aerosol properties in the cloud layer.

  • 34.
    Johansson, Jana H.
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Salter, Matthew E.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Acosta Navarro, Juan Camilo
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, E. Douglas
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Cousins, Ian T.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Global transport of perfluoroalkyl acids via sea spray aerosol2019In: Environmental Science: Processes & Impacts, ISSN 2050-7887, E-ISSN 2050-7895, Vol. 21, no 4, p. 635-649Article in journal (Refereed)
    Abstract [en]

    Perfluoroalkyl acids (PFAAs) are persistent organic pollutants found throughout the world's oceans. Previous research suggests that long-range atmospheric transport of these substances may be substantial. However, it remains unclear what the main sources of PFAAs to the atmosphere are. We have used a laboratory sea spray chamber to study water-to-air transfer of 11 PFAAs via sea spray aerosol (SSA). We observed significant enrichment of all PFAAs relative to sodium in the SSA generated. The highest enrichment was observed in aerosols with aerodynamic diameter < 1.6 mm, which had aerosol PFAA concentrations up to similar to 62 000 times higher than the PFAA water concentrations in the chamber. In surface microlayer samples collected from the sea spray chamber, the enrichment of the substances investigated was orders of magnitude smaller than the enrichment observed in the aerosols. In experiments with mixtures of structural isomers, a lower contribution of branched PFAA isomers was observed in the surface microlayer compared to the bulk water. However, no clear trend was observed in the comparison of structural isomers in SSA and bulk water. Using the measured enrichment factors of perfluorooctanoic acid and perfluorooctane sulfonic acid versus sodium we have estimated global annual emissions of these substances to the atmosphere via SSA as well as their global annual deposition to land areas. Our experiments suggest that SSA may currently be an important source of these substances to the atmosphere and, over certain areas, to terrestrial environments.

  • 35.
    Johansson, Jana
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Salter, Matthew
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Navarro, Juan-Camilo
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Douglas
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Cousins, Ian
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Global transport of perfluoroalkyl acids via sea spray aerosolManuscript (preprint) (Other academic)
  • 36.
    Karl, Matthias
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology.
    Gross, Allan
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology.
    Pirjola, Liisa
    Intercomparison of dimethylsulfide oxidation mechanism for the marine boundary layer: Gaseous and particulate sulfur constituents2007In: Journal of Geophysical Research-Atmospheres, ISSN 0148-0227, Vol. 112, no D15, p. D15304-Article in journal (Refereed)
    Abstract [en]

    An intercomparison of seven dimethylsulfide oxidation chemical mechanisms for the marine boundary layer (MBL) is conducted using a coupled gas phase/aerosol box model.

    The mechanisms are from Koga and Tanaka (1993), Hertel et al. (1994), Saltelli and Hjorth (1995), Chin et al. (1996), Capaldo and Pandis (1997), Lucas and Prinn (2002), and the mechanism developed during the Evaluation of the Climatic Impact of Dimethyl Sulfide project (EL CID, 2003). They range from schemes with very detailed description

    of the dimethylsulfide oxidation with up to 65 reactions to a very simple scheme with only six reactions suitable for global modeling. Coupling each oxidation mechanism to a monodisperse aerosol dynamics model allows for the simultaneous comparison of predicted gas phase and particulate concentrations of sulfur-containing constituents, together with the predicted contribution of dimethylsulfide (DMS) to aerosol formation

    and growth. Significant differences for sulfur-containing compounds between the compared schemes are observed. The temperature dependence and magnitude of the ratio between methane sulfonate and non-sea-salt sulfate is investigated for each scheme and compared to observations. Liquid phase oxidation processes are missing in the model

    and the capability of individual schemes to correctly predict observed ratios can only be assessed in part. No new particle formation was found when applying binary nucleation in the three marine boundary layer scenarios. Therefore the results suggest that several uncertainties limiting our understanding of atmospheric oxidation of dimethylsulfide with implications for climate still exist.

  • 37. Karl, Matthias
    et al.
    Gross, Allan
    Pirjola, Liisa
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    A new flexible multicomponent model for the study of aerosol dynamics in the marine boundary layer2011In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 63, no 5, p. 1001-1025Article in journal (Refereed)
    Abstract [en]

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

  • 38. Karl, Matthias
    et al.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Coz, Esther
    Heintzenberg, Jost
    Marine nanogels as a source of atmospheric nanoparticles in the high Arctic2013In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 40, no 14, p. 3738-3743Article in journal (Refereed)
    Abstract [en]

    The high Arctic (north of 80 degrees N) in summer is a region characterized by clean air and low abundances of preexisting particles. Marine colloidal nanogels i.e., assembled dissolved organic carbohydrate polymer networks have recently been confirmed to be present in both airborne particles and cloud water over the Arctic pack ice area. A novel route to atmospheric nanoparticles that appears to be operative in the high Arctic is suggested. It involves the injection of marine granular nanogels into the air from evaporating fog and cloud droplets, and is supported by observational and theoretical evidence obtained from a case study. Statistical analysis of the aerosol size distribution data recorded in the years 1991, 1996, 2001, and 2008 classified 75nanoparticle eventscovering 17% of the observed time periodas nanogel-type events, characterized by the spontaneous appearance of several distinct size bands below 200nm diameter.

  • 39. Karl, Matthias
    et al.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gross, Allan
    Pirjola, Liisa
    A study of new particle formation in the marine boundary layer over the central Arctic Ocean using a flexible multicomponent aerosol dynamic model2012In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 64, p. 17158-Article in journal (Refereed)
    Abstract [en]

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

  • 40. Karl, Matthias
    et al.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Mashayekhy Rad, Farshid
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Backlund, Are
    Lopez-Aparicio, Susana
    Heintzenberg, Jost
    New insights in sources of the sub-micrometre aerosol at Mt. Zeppelin observatory (Spitsbergen) in the year 20152019In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 71, no 1, p. 1-29Article in journal (Refereed)
    Abstract [en]

    In order to evaluate the potential impact of the Arctic anthropogenic emission sources it is essential to understand better the natural aerosol sources of the inner Arctic and the atmospheric processing of the aerosols during their transport in the Arctic atmosphere. A 1-year time series of chemically specific measurements of the sub-micrometre aerosol during 2015 has been taken at the Mt. Zeppelin observatory in the European Arctic. A source apportionment study combined measured molecular tracers as source markers, positive matrix factorization, analysis of the potential source distribution and auxiliary information from satellite data and ground-based observations. The annual average sub-micrometre mass was apportioned to regional background secondary sulphate (56%), sea spray (17%), biomass burning (15%), secondary nitrate (5.8%), secondary marine biogenic (4.5%), mixed combustion (1.6%), and two types of marine gel sources (together 0.7%). Secondary nitrate aerosol mainly contributed towards the end of summer and during autumn. During spring and summer, the secondary marine biogenic factor reached a contribution of up to 50% in some samples. The most likely origin of the mixed combustion source is due to oil and gas extraction activities in Eastern Siberia. The two marine polymer gel sources predominantly occurred in autumn and winter. The small contribution of the marine gel sources at Mt. Zeppelin observatory in summer as opposed to regions closer to the North Pole is attributed to differences in ocean biology, vertical distribution of phytoplankton, and the earlier start of the summer season.

  • 41. Karl, Matthias
    et al.
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Mashayekhy Rad, Farshid
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Bäcklund, Are
    Lopez-Aparicio, Susana
    Heintzenberg, Jost
    Sources of the sub-micrometre aerosol at Mt. Zeppelin Observatory (Spitsbergen) in the year 2015: Indication for ice-related marinegelsManuscript (preprint) (Other academic)
  • 42.
    Kupiszewski, Pjotr
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . Paul Scherrer Institute, Switzerland .
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Sjögren, S.
    Sedlar, J.
    Graus, M.
    Mueller, M.
    Brooks, B.
    Swietlicki, E.
    Norris, S.
    Hansel, A.
    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.

  • 43.
    Leck, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Bigg, E. Keith
    Stockholm University, Faculty of Science, Department of Meteorology .
    A modified aerosol-cloud-climate feedback hypothesis2007In: Environmental Chemistry, ISSN 1448-2517, E-ISSN 1449-8979, Vol. 4, no 6, p. 400-403Article in journal (Refereed)
    Abstract [en]

    Problems with the aerosol–cloud–climate feedback process known as the ‘CLAW’ hypothesis are discussed and a modified scheme that poses a stronger possible link between marine biology, cloud properties and climate than is provided by dimethyl sulfide alone is proposed.

  • 44.
    Leck, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology. Kemisk meteorologi.
    Bigg, E. Keith
    Comparison of sources and nature of the tropical aerosol with the summer high Arctic aerosol2008In: Tellus. Series B: Chemical and physical meteorology, Vol. 60, no 1, p. 118-126Article in journal (Refereed)
    Abstract [en]

    Marine aerosol was collected in September 1998 and July 2005 on the upwind coast of an island at latitude 15◦ S, about 15 km downwind from the outer edge of the Great Barrier Reef, Australia, and examined by electron microscopy.

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

  • 45.
    Leck, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Bigg, E. Keith
    New Particle Formation of Marine Biological Origin2010In: Aerosol Science and Technology, ISSN 0278-6826, E-ISSN 1521-7388, Vol. 44, no 7, p. 570-577Article in journal (Refereed)
    Abstract [en]

    Large increases in concentration of particles smaller than 20 nm diameter are relatively common over the central Arctic Ocean in summer and have occasionally been observed over lower latitude oceans. These events often do not readily fit theoretical models of homogeneous nucleation from known precursor gases. It is shown that aggregates and gels of marine biological origin are often common over remote oceans and have a partially granular structure. Previous work in the central Arctic Ocean in summer has shown evidence of release of particles of the order of 40 nm diameter in the presence of evaporating fogs. It is suggested here that under some circumstances disintegration of the primary particles may be more complete, releasing particles smaller than 5 nm that would then be mistaken for recently nucleated particles. Examination of particles present during an apparent nucleation event at Cape Grim, Tasmania supports this interpretation. Correlation coefficients of concentrations of particles of different sizes during the period before apparent nucleation events suggests a distinct difference between vigorous true nucleation events and those over the central Arctic Ocean in summer where little subsequent growth is observed.

  • 46.
    Leck, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gao, Qiuju
    Stockholm University, Faculty of Science, Department of Meteorology .
    Mashayekhy Rad, Farshid
    Stockholm University, Faculty of Science, Department of Meteorology . Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Nilsson, Ulrika
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    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 mu m 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 supermicrometer 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.

  • 47.
    Leck, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Qiuju, Gao
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nilsson, Ulrika
    Stockholm University, Faculty of Science, Department of Analytical Chemistry.
    Size-resolved polysaccharides in summer high Arctic aerosol relevant to cloud formation.Manuscript (preprint) (Other academic)
  • 48.
    Leck, Caroline
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Svensson, E.
    Stockholm University, Faculty of Science, Department of Meteorology .
    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)
    Abstract [en]

    Concentrations of cloud condensation nuclei (CCN) were measured throughout an expedition by icebreaker around the central Arctic Ocean, including a 3 week ice drift operation at 87 degrees N, from 3 August to 9 September 2008. In agreement with previous observations in the area and season, median daily CCN concentrations at 0.2% water vapour supersaturation (SS) were typically in the range of 15 to 30 cm(-3), but concentrations varied by 2 to 3 orders of magnitude over the expedition and were occasionally below 1 cm(-3). The CCN concentrations were highest near the ice edge and fell by a factor of 3 in the first 48 h of transport from the open sea into the pack ice region. For longer transport times they increased again, indicating a local source over the pack ice, suggested to be polymer gels, via drops injected into the air by bubbles bursting on open leads. We inferred the properties of the unexplained non-water soluble aerosol fraction that was necessary for reproducing the observed concentrations of CCN. This was made possible by assuming Kohler theory and simulating the cloud nucleation process using a Lagrangian adiabatic air parcel model that solves the kinetic formulation for condensation of water on size resolved aerosol particles. We propose that the portion of the internally/externally mixed water insoluble particles was larger in the corresponding smaller aerosol size ranges. These particles were physically and chemically behaving as polymer gels: the interaction of the hydrophilic and hydrophobic entities on the structures of polymer gels during cloud droplet activation would at first only show a partial wetting character and only weak hygroscopic growth. Given time, a high CCN activation efficiency is achieved, which is promoted by the hydrophilicity or surface-active properties of the gels. Thus the result in this study argues that the behaviour of the high Arctic aerosol in CCN-counters operating at water vapour SSs > 0.4% (high relative humidities) may not be properly explained by conventional Kohler theory.

  • 49. Li, Xin
    et al.
    Hede, Thomas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tu, Yaoquan
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ågren, Hans
    Cloud droplet activation mechanisms of amino acid aerosol particles: insight from molecular dynamics simulationsManuscript (preprint) (Other academic)
    Abstract [en]

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

  • 50. Li, Xin
    et al.
    Hede, Thomas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tu, Yaoquan
    Leck, Caroline
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ågren, Hans
    Cloud droplet activation mechanisms of amino acid aerosol particles: insight from molecular dynamics simulations2013In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, p. 65-Article in journal (Refereed)
    Abstract [en]

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

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