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  • 1. Bigg, E K
    et al.
    Leck, C
    Cloud-active particles over the central Arctic Ocean2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, p. 32155-32166Article in journal (Refereed)
    Abstract [en]

    Concentrations of cloud condensation (CCN) and ice forming nuclei (IFN) were measured throughout an expedition by icebreaker around the central Arctic Ocean including the North Pole from July 15 to September 23, 1996. Daily median CCN concentrations at 0.25% supersaturation were typically in the range 15 to 50 cm(-3), but concentrations varied by 3 orders of magnitude over the expedition and commonly by an order of magnitude within a day. They were highest near the ice edge and fell by almost an order of magnitude in the first 36 hours of transport from the open sea into the pack ice region. For longer transport times they increased again indicating a local source, suggested to be drops injected into the air by bubbles bursting on open leads. Median concentrations of IFN ranged from 18 M 3 just inside the pack ice at the beginning of the expedition to 1 m(-3) at the end. The differences with transport time from the ice edge were less marked than for CCN. Comparison of CCN measurements with simultaneously measured number size distributions showed that the median concentration active at a given supersaturation was only 71% of the number expected if at I the particles had been composed of pure ammonium sulfate. Transmission electron microscope observations of individual particles suggested an evolution of many CCN from nonvolatile, nonhygroscopic particles <50 nm by acquisition of the oxidation products of dimethyl sulfide. Cloud processing added further mass. The largest primary source within the pack ice region was deduced to be film drops from bursting bubbles yielding liquid particles with a high organic content and surfactant properties. A relationship between CCN number and sulfur mass is derived which extends previous results to lower CCN numbers and indicates a greater sensitivity to change in sulfate mass than at lower latitudes. Bacteria and probable submicron fragments of marine organisms were identified in the samples and suggested to be the source of IFN.

  • 2. Bigg, E K
    et al.
    Leck, C
    Properties of the aerosol over the central Arctic Ocean2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, p. 32101-32109Article in journal (Refereed)
    Abstract [en]

    Transmission electron microscopy was used to examine the morphology and some physical and chemical properties of individual particles collected north of latitude 80degreesN by impaction or electrostatic precipitation during the period July 21 to September 18, 1996. Particles smaller than 50 nm in diameter showed no evidence of the presence of sulfuric acid, previously believed responsible for new particle formation. Many were crystalline or semicrystalline often with pentagonal or hexagonal habit and more heat resistant than ammonium salts. Most were unaffected by decane or xylene vapor, but some were wholly or partly dissolved, indicating that they were chemically different. Sulfuric acid, ammonia, and probably methane sulfonic acid appeared to be mainly responsible for growth of these particles to the sizes that could become involved in cloud drop formation, about 80-100 nm in diameter. Much greater diversity was present in larger particles, the most numerous class of which usually appeared to be very variable mixtures of sulfuric acid, methane sulfonic acid, and their ammonium salts. All contained significant organic material. Particles containing sea salt were generally larger than 250 nm in diameter and contained an amazing variety of other material, much of it organic. On days with sunshine unusual numbers of particles <5 nm and in the range 10-50 nm in diameter occurred. At the same time, concentrations of three different types of particle with diameters of the order of 100 nm were enhanced. One group was liquid when collected, had a large organic content, and wet the collecting surface. The other two were bacteria and flat insoluble plates some of which contained fragments of diatoms. It is proposed that they were ejected into the air by bubbles bursting on the open leads.

  • 3. Bigg, E K
    et al.
    Leck, C
    Nilsson, E D
    Sudden changes in aerosol and gas concentrations in the central Arctic marine boundary layer: Causes and consequences2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, p. 32167-32185Article in journal (Refereed)
    Abstract [en]

    Measurements of aerosol number size distributions and concentrations of the precursor gases dimethyl sulfide, sulfur dioxide and ammonia were made within the pack ice region of the central Arctic Ocean during July and August 1996 from the icebreaker Oden. Changes in concentration, sometimes exceeding the entire seasonal variation, often occurred within an hour and attempts to find the reasons for them are described. Vertical profiles of aerosol concentration in Aitken and accumulation mode particles obtained on helicopter flights revealed intense concentration gradients in the lowest 1000 m. Those below 100 m were common. Concentrations of accumulation mode particles were usually greater near the surface than at 100 m. Four representative case studies for which vertical aerosol profiles were obtained are presented. Observations of rapid large changes in near-surface concentration of aerosols in different size ranges are compared with the vertical profiles, meteorological information, and acoustic or optical remote sensing to infer processes causing the changes. Comparison of simultaneous variations in aerosols and precursor gas concentrations are used to define the vertical profiles of the gases. It was found that dimethyl sulfide and ammonia concentrations usually must have been strongly depleted near the surface relative to concentrations at about 100 m. Sulfur dioxide profiles appeared to be more complex. Turbulence or vertical air motions initiated by atmospheric wave motions trapped within the stable boundary layer appeared to be directly responsible for many of the sudden concentration changes, through interaction with concentration gradients close to the surface. The presence of low-level jets also had direct or indirect influences on mixing in the lowest few hundred meters. The extent to which aerosols measured near the surface can determine the microphysics of central Arctic marine boundary layer clouds is examined.

  • 4. Bigg, E. Keith
    et al.
    Leck, Caroline
    The composition of fragments of bubbles bursting at the ocean surface2008In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, no D11Article 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.

  • 5. Birch, C. E.
    et al.
    Brooks, I. M.
    Tjernstrom, M.
    Milton, S. F.
    Earnshaw, P.
    Soderberg, S.
    Persson, P. Ola G.
    The performance of a global and mesoscale model over the central Arctic Ocean during late summer2009In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 114Article in journal (Refereed)
    Abstract [en]

    Measurements of turbulent fluxes, clouds, radiation, and profiles of mean meteorological parameters, obtained over an ice floe in the central Arctic Ocean during the Arctic Ocean Experiment 2001, are used to evaluate the performance of U. K. Met Office Unified Model (MetUM) and Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) in the lower atmosphere during late summer. Both the latest version of the MetUM and the version operational in 2001 are used in the comparison to gain an insight as to whether updates to the model have improved its performance over the Arctic region. As with previous model evaluations over the Arctic, the pressure, humidity, and wind fields are satisfactorily represented in all three models. The older version of the MetUM underpredicts the occurrence of low-level Arctic clouds, and the liquid and ice cloud water partitioning is inaccurate compared to observations made during SHEBA. In the newer version, simulated ice and liquid water paths are improved, but the occurrence of low-level clouds are overpredicted. Both versions overestimate the amount of radiative heat absorbed at the surface, leading to a significant feedback of errors involving the surface albedo, which causes a large positive bias the surface temperature. Cloud forcing in COAMPS produces similar biases in the downwelling shortwave and longwave radiation fluxes to those produced by UM(G25). The surface albedo parameterization is, however, more realistic, and thus, the total heat flux and surface temperature are more accurate for the majority of the observation period.

  • 6.
    Divine, D. V.
    et al.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Isaksson, E.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Pohjola, V.
    Uppsala Univ, Dept Earth Sci, SE-75236 Uppsala, Sweden..
    Meijer, H.
    Univ Groningen, Ctr Isotope Res, NL-9714 AG Groningen, Netherlands..
    de Wal, R. S. W. van
    Univ Utrecht, Inst Marine & Atmospher Res Utrecht, NL-3508 TA Utrecht, Netherlands..
    Martma, T.
    Tallinn Univ Technol, Inst Geol, EE-19086 Tallinn, Estonia..
    Moore, J.
    Univ Lapland, Arctic Ctr, FIN-96101 Rovaniemi, Finland..
    Sjogren, B.
    Uppsala Univ, Dept Earth Sci, SE-75236 Uppsala, Sweden..
    Godtliebsen, F.
    Univ Tromso, Dept Math & Stat, N-9037 Tromso, Norway..
    Deuterium excess record from a small Arctic ice cap2008In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, no D19, article id D19104Article in journal (Refereed)
    Abstract [en]

    In this paper we present a deuterium excess (d) record from an ice core drilled on a small ice cap in Svalbard in 1997. The core site is located at Lomonosovfonna at 1255 m asl, and the analyzed time series spans the period 1400-1990 A. D. The record shows pronounced multidecadal to centennial-scale variations coherent with sea surface temperature changes registered in the subtropical to southern middle-latitude North Atlantic during the instrumental period. We interpret the negative trend in the deuterium excess during the 1400s and 1500s as an indication of cooling in the North Atlantic associated with the onset of the Little Ice Age. Consistently positive anomalies of d after 1900, peaking at about 1950, correspond with well-documented contemporary warming. Yet the maximum values of deuterium excess during 1900-1990 are not as high as in the early part of the record (pre-1550). This suggests that the sea surface temperatures during this earlier period of time in the North Atlantic to the south of approximately 45 degrees N were at least comparable with those registered in the 20th century before the end of the 1980s. We examine the potential for a cold bias to exist in the deuterium excess record due to increased evaporation from the local colder sources of moisture having isotopically cold signature. It is argued that despite a recent oceanic warming, the contribution from this local moisture to the Lomonosovfonna precipitation budget is still insufficient to interfere with the isotopic signal from the primary moisture region in the midlatitude North Atlantic.

  • 7.
    Forsstrom, S.
    et al.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway..
    Isaksson, E.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway..
    Skeie, R. B.
    CICERO, Oslo, Norway..
    Ström, J.
    Stockholm Univ, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    Pedersen, C. A.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway..
    Hudson, S. R.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway..
    Berntsen, T. K.
    CICERO, Oslo, Norway.;Univ Oslo, Fac Math & Nat Sci, Oslo, Norway..
    Lihavainen, H.
    Finnish Meteorol Inst, FIN-00101 Helsinki, Finland..
    Godtliebsen, F.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway.;Univ Tromso, Fac Sci & Technol, Tromso, Norway..
    Gerland, S.
    Norwegian Polar Res Inst, N-9005 Tromso, Norway..
    Elemental carbon measurements in European Arctic snow packs2013In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 118, no 24, p. 13614-13627Article in journal (Refereed)
  • 8.
    Forsstrom, S.
    et al.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Ström, J.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway.;Stockholm Univ, Dept Appl Environm Sci ITM, SE-10691 Stockholm, Sweden..
    Pedersen, C. A.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Isaksson, E.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Gerland, S.
    Norwegian Polar Res Inst, Polar Environm Ctr, N-9296 Tromso, Norway..
    Elemental carbon distribution in Svalbard snow2009In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 114, article id D19112Article in journal (Refereed)
    Abstract [en]

    The concentration of apparent elemental carbon (ECa, based on a thermal-optical method) in the snow was investigated in Svalbard (European Arctic) during spring 2007. The median ECa concentration of 81 samples was 4.1 mu g l(-1) and the values ranged from 0 to 80.8 mu g l(-1) of melt water. The median concentration is nearly an order of magnitude lower than the previously published data of equivalent black carbon (BCe, based on an optical method), obtained from Svalbard snow in the 1980s. A systematic regional difference was evident: ECa concentrations were higher in east Svalbard compared to west Svalbard. The observations of snow ECa cover spatial scales up to several hundred kilometers, which is comparable to the resolution of many climate models. Measurements of atmospheric carbonaceous aerosol (2002-2008) at Zeppelin station in Ny-Alesund, Svalbard, were divided to air mass sectors based on calculated back trajectories. The results show that air originating from the eastern sector contains more than two and half times higher levels of soot than air arriving from south to west. The observed east-west gradient of ECa concentrations in snow may be because of a combination of the atmospheric concentration gradient, the orographic effect of the archipelago, and the efficient scavenging of the carbonaceous particles through precipitation.

  • 9. Grinsted, A
    et al.
    Moore, J C
    Pohjola, V
    Martma, T
    Isaksson, E
    Svalbard summer melting, continentality, and sea ice extent from the Lomonosovfonna ice core2006In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, no D7, article id D07110Article in journal (Refereed)
    Abstract [en]

    We develop a continentality proxy (1600-1930) based on amplitudes of the annual signal in oxygen isotopes in an ice core. We show via modeling that by using 5 and 15 year average amplitudes the effects of diffusion and varying layer thickness can be minimized, such that amplitudes then reflect real seasonal changes in delta O-18 under the influence of melt. A model of chemical fractionation in ice based on differing elution rates for pairs of ions is developed as a proxy for summer melt (1130-1990). The best pairs are sodium with magnesium and potassium with chloride. The continentality and melt proxies are validated against twentieth-century instrumental records and longer historical climate proxies. In addition to summer temperature, the melt proxy also appears to reflect sea ice extent, likely as a result of sodium chloride fractionation in the oceanic sea ice margin source area that is dependent on winter temperatures. We show that the climate history they depict is consistent with what we see from isotopic paleothermometry. Continentality was greatest during the Little Ice Age but decreased around 1870, 20-30 years before the rise in temperatures indicated by the delta O-18 profile. The degree of summer melt was significantly larger during the period 1130-1300 than in the 1990s.

  • 10. Hillamo, R
    et al.
    Kerminen, V M
    Aurela, M
    Makela, T
    Maenhaut, W
    Leck, C
    Modal structure of chemical mass size distribution in the high Arctic aerosol2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D21, p. 27555-27571Article in journal (Refereed)
    Abstract [en]

    Chemical mass size distributions of aerosol particles were measured in the remote marine boundary layer over the central Arctic Ocean as part of the Atmospheric Research Program on the Arctic Ocean Expedition 1996 (AOE-96). An inertial impaction method was used to classify aerosol particles into different size classes for subsequent chemical analysis. The particle chemical composition was determined by ion chromatography and by the particle-induced X-ray emission technique. Continuous particle size spectra were extracted from the raw data using a data inversion method. Clear and varying modal structures for aerosols consisting of primary sea-salt particles or of secondary particles related to dimethyl sulfide emissions were found. Concentration levels of all modes decreased rapidly when the distance from open sea increased. In the submicrometer size range the major ions found by ion chromatography were sulfate, methane sulfonate, and ammonium. They had most of the time a clear Aitken mode and one or two accumulation modes, with aerodynamic mass median diameters around 0.1 mum, 0.3 mum, and between 0.5-1.0 mum, respectively. The overall submicron size distributions of these three ions were quite similar, suggesting that they were internally mixed over most of this size range. The corresponding modal structure was consistent with the mass size distributions derived from the particle number size distributions measured with a differential mobility particle sizer. The Aitken to accumulation mode mass ratio for nss-sulfate and MSA was substantially higher during clear skies than during cloudy periods. Primary sea-salt particles formed a mode with an aerodynamic mass median diameter around 2 mum. In general, the resulting continuous mass size distributions displayed a clear modal structure consistent with our understanding of the two known major source mechanisms. One is the sea-salt aerosol emerging from seawater by bubble bursting. The other is related to dimethylsulfide (DMS) emissions from biogenic processes in seawater, followed by gas-to-particle conversion, formation of particulate sulfate and methane sulfonate (MSA) and neutralization by ammonia.

  • 11. Kekonen, T
    et al.
    Moore, J
    Peramaki, P
    Mulvaney, R
    Isaksson, E
    Pohjola, V
    van de Wal, R S W
    The 800 year long ion record from the Lomonosovfonna (Svalbard) ice core2005In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 110, no D7, article id D07304Article in journal (Refereed)
    Abstract [en]

    We present a high-resolution record of water-soluble ion chemistry from a 121 m ice core spanning about 800 years. The core is well dated to 2/3 depth using cycle counting and reference horizons and a simple but close fitting model for the lower 1/3 of the core. This core suffers from modest seasonal melt, and so we present concentration data in decadal running means to minimize percolation effects. Sea-salt ions (Na+, Cl-, Mg2+, and K+) account for more than 70% of all ions. In general, sea-salt ion concentrations are rather variable and have no clear association with climatic variations. Sulfate, with 74% being from non-sea-salt sources, has higher concentrations than seen on Vestfonna ice cap but lower than in Ny-angstrom lesund aerosols, suggesting central Spitsbergen receives more marine (westerly) air masses than Ny-angstrom lesund but more sulfate enriched (easterly) air masses than Nordaustlandet. Clear anthropogenic impacts are found for sulfate, nitrate, and ammonium (and probably excess chloride) after the mid twentieth century, with sulfate showing a significant rise by the end of the nineteenth century. Sulfate and methanesulfonate concentrations correlate well during the twentieth century, and it is clear that most of the preindustrial sulfate is of biogenic origin. Terrestrial component (Ca2+) has the highest concentrations in the coldest part of the Little Ice Age, suggesting more windy conditions, transporting local terrestrial dust to the ice cap. All ion concentrations decrease at the end of the twentieth century, which reflects loss of ions by runoff, with non-sea-salt magnesium being particularly sensitive to melting.

  • 12. Kerminen, V M
    et al.
    Leck, C
    Sulfur chemistry over the central Arctic Ocean during the summer: Gas-to-particle transformation2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, p. 32087-32099Article in journal (Refereed)
    Abstract [en]

    Atmospheric gas-to-particle transformation of the oxidation products of dimethyl sulfide (DMS) was investigated over the central Arctic Ocean by using observational data and a coupled gas phase chemistry-aerosol dynamics model. Chemical compounds investigated were sulfuric acid (H2SO4(g)), methasulfonic acid (MSA(g)), and sulfur dioxide (SO2(g)) in the gas phase, and non-sea-salt sulfate (nss-SO42-) and MSA in the particulate phase. During the advection from the open ocean to over the pack ice region, the particulate phase was found to be influenced significantly by three processes: (1) rapid removal of particulate matter during the first 1-2 days of advection, (2) continual formation of particulate nss-SO42- and MSA, and (3) local production of particles consisting mostly of matter other than nss-SO42- and MSA over the pack ice. In the absence of clouds and fogs, the principal sink for the vapors H2SO4(g) and MSA(g) were their condensational transport to submicron particles. SO2(g) was influenced significantly by both dry deposition and gas phase oxidation. Although there is a local source of coarse sea-salt particles within the pack ice region, the role of these particles in the budgets of nss-SO42- and SO2(g), and probably also in the budget of MSA, is only minor, especially when compared with marine regions at lower latitudes. The performance of the DMS gas-phase chemistry scheme was tested against field data using a measurement case influenced minimally by clouds/fogs and the free troposphere. The predicted concentration of nss-SO42- was within the uncertainties of the analysis, whereas that of MSA was high by a factor of 3-6. This demonstrates that not only heterogeneous reactions involved in atmospheric DMS chemistry but also certain gas-phase reactions require further investigation.

  • 13.
    Korhonen, Hannele
    et al.
    Univ Leeds, Sch Earth & Environm, Leeds LS2 9JT, W Yorkshire, England..
    Carslaw, Kenneth S.
    Univ Leeds, Sch Earth & Environm, Leeds LS2 9JT, W Yorkshire, England..
    Spracklen, Dominick V.
    Univ Leeds, Sch Earth & Environm, Leeds LS2 9JT, W Yorkshire, England..
    Ridley, David A.
    Univ Leeds, Sch Earth & Environm, Leeds LS2 9JT, W Yorkshire, England..
    Ström, Johan
    Univ Stockholm, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    A global model study of processes controlling aerosol size distributions in the Arctic spring and summer2008In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, no D8, article id D08211Article in journal (Refereed)
    Abstract [en]

    We use a global chemical transport model (CTM) with size-resolved aerosol microphysics to evaluate our understanding of the processes that control Arctic aerosol, focussing on the seasonal changes in the particle size distribution during the transition from Arctic haze in spring to cleaner conditions in summer. This period presents several challenges for a global model simulation because of changes in meteorology, which affect transport pathways and precipitation scavenging rates, changes in the ocean-atmosphere flux of trace gases and particulates associated with sea ice break-up and increased biological activity, and changes in photolysis and oxidation rates which can affect particle nucleation and growth rates. Observations show that these changes result in a transition from an accumulation mode-dominated aerosol in spring to one dominated by Aitken and nucleation mode particles in summer. We find that remote Arctic aerosol size distribution is very sensitive to the model treatment of wet removal. In order to simulate the high accumulation mode concentrations typical of winter and spring it was necessary to substantially reduce the scavenging of these particles during transport. The resulting increases in accumulation mode lead to improvement in the modeled Aitken mode particle concentrations (which fall, due to increased scavenging in the free troposphere) and produce aerosol optical depths in good agreement with observations. The summertime increase in nucleation and Aitken mode particles is consistent with changes in local aerosol nucleation rates driven mainly by increased photochemical production of sulphuric acid vapor and, to a lesser extent, by decreases in the condensation sink as Arctic haze decreases. Alternatively, to explain the observed summertime Aitken mode particle concentrations in terms of ultrafine sea spray particles requires a sea-air flux a factor 5-25 greater than predicted by current wind speed and sea surface temperature dependent flux parameterizations. The enhanced total flux is clearly higher than measured in the Arctic and cannot explain the observed nucleation mode in the high Arctic. The model suggests that the summertime source of Aitken particles has very little effect on the accumulation mode and aerosol optical depth but they may contribute to cloud condensation nuclei in clouds with updraught velocities greater than about 15 cm/s. From a global aerosol modeling perspective, our understanding of Arctic aerosol is poor. We suggest several processes that currently limit our ability to simulate this challenging environment.

  • 14. Leck, C
    et al.
    Nilsson, E D
    Bigg, E K
    Backlin, L
    Atmospheric program on the Arctic Ocean Expedition 1996 (AOE-96): An overview of scientific goals, experimental approach, and instruments2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, p. 32051-32067Article in journal (Refereed)
    Abstract [en]

    The broad aim of the atmospheric program on an expedition to the central Arctic Ocean during July-September 1996 (AOE-96) was to improve the accuracy of models predicting climatic change by reducing uncertainties associated with the indirect climate effect of aerosols. A major part of this aim was to assess what feedback processes might be involved and their implications for both regional and global radiative forcing. An immediate objective therefore was to study the biogeochemical sources that were thought to lead to aerosol formation and possible growth processes as well as the characterization of the aerosol that actually influences cloud properties in a region where natural processes prevailed. The program was designed as an integrated package to study processes from the sea-ice/air interface to the top of the Arctic boundary layer and involved the contribution from about 25 participating scientists from 8 countries. The results from a previous expedition to the same area were used to specify the research topics from which new or improved information was needed to achieve the objectives. The instruments, techniques, and models developed and deployed to provide the answers are described. The relevant properties of the region, the route of the expedition, the conditions encountered, and the special circumstances of measurements made on an ice floe are also discussed.

  • 15.
    Moore, J. C.
    et al.
    Beijing Normal Univ, Coll Global Change & Earth Syst Sci, Beijing 100875, Peoples R China.;Univ Lapland, Arctic Ctr, FI-96101 Rovaniemi, Finland.;Uppsala Univ, Dept Earth Sci, SE-75236 Uppsala, Sweden..
    Beaudon, E.
    Univ Lapland, Arctic Ctr, FI-96101 Rovaniemi, Finland..
    Kang, Shichang
    Chinese Acad Sci, Key Lab Tibetan Environm Changes & Land Surface P, Inst Tibetan Plateau Res, Beijing 100085, Peoples R China.;Chinese Acad Sci, State Key Lab Cryospher Sci, Lanzhou, Peoples R China..
    Divine, D.
    Univ Tromso, Dept Math & Stat, N-9018 Tromso, Norway..
    Isaksson, E.
    Norwegian Polar Res Inst, N-9296 Tromso, Norway..
    Pohjola, V. A.
    Uppsala Univ, Dept Earth Sci, SE-75236 Uppsala, Sweden..
    van de Wal, R. S. W.
    Univ Utrecht, Inst Marine & Atmospher Res, NL-3508 TA Utrecht, Netherlands..
    Statistical extraction of volcanic sulphate from nonpolar ice cores2012In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 117, article id D03306Article in journal (Refereed)
    Abstract [en]

    Ice cores from outside the Greenland and Antarctic ice sheets are difficult to date because of seasonal melting and multiple sources (terrestrial, marine, biogenic and anthropogenic) of sulfates deposited onto the ice. Here we present a method of volcanic sulfate extraction that relies on fitting sulfate profiles to other ion species measured along the cores in moving windows in log space. We verify the method with a well dated section of the Belukha ice core from central Eurasia. There are excellent matches to volcanoes in the preindustrial, and clear extraction of volcanic peaks in the post-1940 period when a simple method based on calcium as a proxy for terrestrial sulfate fails due to anthropogenic sulfate deposition. We then attempt to use the same statistical scheme to locate volcanic sulfate horizons within three ice cores from Svalbard and a core from Mount Everest. Volcanic sulfate is < 5% of the sulfate budget in every core, and differences in eruption signals extracted reflect the large differences in environment between western, northern and central regions of Svalbard. The Lomonosovfonna and Vestfonna cores span about the last 1000 years, with good extraction of volcanic signals, while Holtedahlfonna which extends to about AD1700 appears to lack a clear record. The Mount Everest core allows clean volcanic signal extraction and the core extends back to about AD700, slightly older than a previous flow model has suggested. The method may thus be used to extract historical volcanic records from a more diverse geographical range than hitherto.

  • 16. Nilsson, E D
    et al.
    Barr, S
    Effects of synoptic patterns on atmospheric chemistry and aerosols during the Arctic Ocean Expedition 19962001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, p. 32069-32086Article in journal (Refereed)
    Abstract [en]

    The atmospheric program on the Arctic Ocean Expedition of July through September 1996 (AOE-96) was focused on aerosol climate feedback. The expedition took place close to the saddle point between a semipersistent anticyclonic ridge from near Scandinavia to the Arctic coast of eastern Siberia and a trough from the Canadian archipelago across the pole to north central Siberia. The weather varied from anticyclonic clear-sky conditions to cyclonic cloudy conditions, and 13 identifiable migratory features (frontal bands, wave disturbances) clearly influenced local weather, clouds, atmospheric transport, and chemistry. This includes an explosive polar cyclone, born at the lateral heat gradient between Greenland and the pack ice rather than between open sea and the pack ice. The synoptic scale weather systems caused the strongest variability in trace gases (O-3 in particular) and aerosols, and also strong variability in the cloud cover. The formation of air masses over the pack ice primarily depends on if there is cyclonic (convergent) or anticyclonic (divergent) flow. Cyclonic flow resulted in a modified marine air mass loaded with vapor, but with low aerosol number concentrations owing to frequent clouds and fogs and efficient cloud scavenging of the aerosol. Anticyclonic flow resulted in almost continental air masses with clear sky, long residence time over the pack ice and subsidence slowly replacing the boundary layer with free tropospheric air, low vapor concentrations, but large aerosol number in lack of efficient cloud scavenging. The synoptic variability and advection from south of the ice edge were weaker than during the predecessor International Arctic Ocean Expedition in 1991 (IAOE-91), when on average the sampled air spent 55 hours over the pack ice compared to more than 120 hours during AOE-96, owing to exceptionally high cyclone activity in 1991. This caused a large difference in atmospheric transport, chemistry, and aerosols between the two expeditions.

  • 17. Nilsson, E D
    et al.
    Rannik, U
    Turbulent aerosol fluxes over the Arctic Ocean 1. Dry deposition over sea and pack ice2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, p. 32125-32137Article in journal (Refereed)
    Abstract [en]

    An eddy-covariance flux measurement system was applied successfully to measure aerosol number dry deposition over open sea, ice floes, and over the leads in between the ice floes during the Arctic Ocean Expedition 1996. The aerosol number dry deposition velocity geometric mean was 1.9x10(-3) In s(-1) for the open sea. The dry deposition velocity to the ice floes averaged approximately 3 x 10(-4) ms(-1) with no significant difference between the melting summer ice and frozen, partly snow-covered ice in the early freeze-up. Over the leads the dry deposition velocity was 3.4 x 10(-4) and 9.1 x 10(-4) m s(-1) for the summer and the freeze-up period, respectively. For neutral and stable stratification the geometric averages were 6.5 x 10(-4) and 2.9 x 10(-4) m s(-1), respectively. The dry deposition changed mainly with friction velocity and particle size, as expected from theory, and with static stability, and we are able to recommend an empirical parameterization that works reasonable well over the Arctic Ocean pack ice. The resistance through the quasi-laminar sublayer dominated over the aerodynamic resistance and the ultrafine and Aitken mode particles dominated the dry deposition flux. The average turnover time for the submicometer aerosol in the boundary layer was only 4.6 days, but for cases when the ultrafine and Aitken modes dominated the aerosol size spectra, the turnover times were 1.3 and 3.5 days, respectively. The small turnover times were largely caused by the shallow boundary layer over the Arctic Ocean pack ice.

  • 18. Nilsson, E D
    et al.
    Rannik, U
    Swietlicki, E
    Leck, C
    Aalto, P P
    Zhou, J
    Norman, M
    Turbulent aerosol fluxes over the Arctic Ocean 2. Wind-driven sources from the sea2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, p. 32139-32154Article in journal (Refereed)
    Abstract [en]

    An eddy-covariance flux system was successfully applied over open sea, leads and ice floes during the Arctic Ocean Expedition in July-August 1996. Wind-driven upward aerosol number fluxes were observed over open sea and leads in the pack ice. These particles must originate from droplets ejected into the air at the bursting of small air bubbles at the water surface. The source flux F (in 10(6) m(-2)s(-1)) had a strong dependency on wind speed, log(F) = 0.20 (U) over bar - 1.71 and 0.11 (U) over bar -1.93, over the open sea and leads, respectively (where U is the local wind speed at about 10 in height). Over the open sea the wind-driven aerosol source flux consisted of a film drop mode centered at similar to100 nm diameter and a jet drop mode centered at similar to1 mum diameter. Over the leads in the pack ice, a jet drop mode at similar to2 mum diameter dominated. The jet drop mode consisted of sea-salt, but oxalate indicated an organic contribution, and bacterias and other biogenic particles were identified by single particle analysis. Particles with diameters less than similar to100 nm appear to have contributed to the flux, but their chemical composition is unknown. Whitecaps were probably the bubble source at open sea and on the leads at high wind speed, but a different bubble source is needed in the leads owing to their small fetch. Melting of ice in the leads is probably the best candidate. The flux over the open sea was of such a magnitude that it could give a significant contribution to the condensation nuclei (CCN) population. Although the flux from the leads were roughly an order of magnitude smaller and the leads cover only a small fraction of the pack ice, the local source may till be important for the CCN population in Arctic fogs. The primary marine aerosol source will increase both with increased wind speed and with decreased ice fraction and extent. The local CCN production may therefore increase and influence cloud or fog albedo and lifetime in response to greenhouse warming in the Arctic Ocean region.

  • 19.
    Pedersen, C. A.
    et al.
    Norwegian Polar Res Inst, Tromso, Norway..
    Gallet, J. -C
    Ström, J.
    Stockholm Univ, ITM, Dept Appl Environm Sci, S-10691 Stockholm, Sweden..
    Gerland, S.
    Norwegian Polar Res Inst, Tromso, Norway..
    Hudson, S. R.
    Norwegian Polar Res Inst, Tromso, Norway..
    Forsström, S.
    Norwegian Polar Res Inst, Tromso, Norway..
    Isaksson, E.
    Norwegian Polar Res Inst, Tromso, Norway..
    Berntsen, T. K.
    Univ Oslo, Fac Math & Nat Sci, Dept Geosci, Oslo, Norway..
    In situ observations of black carbon in snow and the corresponding spectral surface albedo reduction2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 4, p. 1476-1489Article in journal (Refereed)
    Abstract [en]

    Black carbon (BC) particles emitted from incomplete combustion of fossil fuel and biomass and deposited on snow and ice darken the surface and reduce the surface albedo. Even small initial surface albedo reductions may have larger adjusted effects due to snow morphology changes and changes in the sublimation and snow melt rate. Most of the literature on the effect of BC on snow surface albedo is based on numerical models, and few in situ field measurements exist to confirm this reduction. Here we present an extensive set of concurrent in situ measurements of spectral surface albedo, BC concentrations in the upper 5 cm of the snowpack, snow physical parameters (grain size and depth), and incident solar flux characteristics from the Arctic. From this data set (with median BC concentrations ranging from 5 to 137 ng BC per gram of snow) we are able to separate the BC signature on the snow albedo from the natural snow variability. Our measurements show a significant correlation between BC in snow and spectral surface albedo. Based on these measurements, parameterizations are provided, relating the snow albedo, as a function of wavelength, to the equivalent BC content in the snowpack. The term equivalent BC used here is the elemental carbon concentration inferred from the thermo-optical method adjusted for the fraction of non-BC constituents absorbing sunlight in the snow. The first parameterization is a simple equation which efficiently describes the snow albedo reduction due to the equivalent BC without including details on the snow or BC microphysics. This can be used in models when a simplified description is needed. A second parameterization, including snow grain size information, shows enhanced correspondence with the measurements. The extracted parameterizations are valid for wavelength bands 400-900 nm, constrained for BC concentrations between 1 and 400 ng g(-1), and for an optically thick snowpack. The parameterizations are purely empirical, and particular focus was on the uncertainties associated with the measurements, and how these uncertainties propagate in the parameterizations. Integrated, the first parameterization (based only on the equivalent BC) gives a broadband (400-900 nm) snow albedo reduction of 0.004 due to 10 ng equivalent BC per gram of snow, while the effect is almost 5 times larger for BC concentrations 1 order of magnitude higher. The study shows that the reconstructed albedo from the second parameterization (including information on the snow grain size) corresponds better to the radiative transfer model Snow, Ice, and Aerosol Radiation albedo than the reconstructed albedo from the first parameterization (excluding grain size information).

  • 20. Pohjola, V A
    et al.
    Moore, J C
    Isaksson, E
    Jauhiainen, T
    van de Wal, R S W
    Martma, T
    Meijer, H A J
    Vaikmae, R
    Effect of periodic melting on geochemical and isotopic signals in an ice core from Lomonosovfonna, Svalbard2002In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 107, no D4, article id 4036Article in journal (Refereed)
    Abstract [en]

    [1] We examine the quality of atmospherically deposited ion and isotope signals in an ice core taken from a periodically melting ice field, Lomonosovfonna in central Spitsbergen, Svalbard. The aim is to determine the degree to which the signals are altered by periodic melting of the ice. We use three diagnostics: (1) the relation between peak values in the ice chemical and isotopic record and ice facies type, (2) the number of apparent annual cycles in these records compared with independently determined number of years represented in the ice core, and (3) a statistical comparison of the isotopic record in the ice core and the isotope records from coastal stations from the same region. We find that during warm summers, as much as 50% of the annual accumulation may melt and percolate into the firn; in a median year this decreases to similar to25%. As a consequence of percolation, the most mobile acids show up to 50% higher concentrations in bubble-poor ice facies compared with facies that are less affected by melt. Most of the other chemical species are less affected than the strong acids, and the stable water isotopes show little evidence of mobility. Annual or biannual cycles are detected in most parameters, and the water isotope record has a comparable statistical distribution to isotopic records from coastal stations. We conclude that ice cores from sites like Lomonosovfonna contain a useful environmental record, despite melt events and percolation and that most parameters preserve an annual, or in the worst cases, a biannual atmospheric signal.

  • 21.
    Silvergren, S.
    et al.
    Lund Univ, Lund, Sweden.;Stockholm Univ, S-10691 Stockholm, Sweden..
    Wideqvist, U.
    Stockholm Univ, S-10691 Stockholm, Sweden..
    Ström, J.
    Stockholm Univ, S-10691 Stockholm, Sweden..
    Sjögren, S.
    Univ Appl Sci Northwestern Switzerland, Brugg, Switzerland..
    Svenningsson, B.
    Lund Univ, Lund, Sweden..
    Hygroscopic growth and cloud forming potential of Arctic aerosol based on observed chemical and physical characteristics (a 1 year study 2007-2008)2014In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 119, no 24, p. 14080-14097Article in journal (Refereed)
    Abstract [en]

    Aerosol particle samples were collected, and the particle size distribution was measured during 1 year at the Zeppelin station (474 m asl) on Svalbard. The chemical constituents, hygroscopicity, and cloud forming properties of the aerosol were analyzed. The aerosol contained mostly sulfate and nitrate during the summer, whereas from September to February the main components were sodium and chloride. The highest concentration (20%) of water-soluble organic matter was sampled in December. The hygroscopic growth factors for the water-soluble fraction were 1.56-2.01 at 90% relative humidity, peaking in October, when the measured supersaturations needed for cloud drop formation were also the lowest. Sea-salt components showed a positive correlation with the cloud forming capability, whereas the organic content had no correlation. The hygroscopicity factors, or kappa values, were determined in three ways for each month: (1)kappa(H-TDMA) from measurements of the hygroscopic growth of particles produced from atomization of the filter extracts, (2)kappa(CCNC) from measurements of the critical supersaturation as a function of size for these particles, and (3)kappa(chem) was modeled based on the organic and inorganic composition of the filter samples. Using the measured particle size distributions and the critical activation diameters from the Cloud Condensation Nuclei Counter (CCNC) measurements, it was found that the number of CCN varied more with supersaturation during the summer months. The best agreement between all three kappa values was in December and January. Comparisons with earlier studies do not suggest any trend in the Arctic aerosol seasonal variability over the last decade.

  • 22. Stohl, A.
    et al.
    Andrews, E.
    Burkhart, J. F.
    Forster, C.
    Herber, A.
    Hoch, S. W.
    Kowal, D.
    Lunder, C.
    Mefford, T.
    Ogren, J. A.
    Sharma, S.
    Spichtinger, N.
    Stebel, K.
    Stone, R.
    Ström, J.
    Torseth, K.
    Wehrli, C.
    Yttri, K. E.
    Pan-Arctic enhancements of light absorbing aerosol concentrations due to North American boreal forest fires during summer 20042006In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, no D22, article id D22214Article in journal (Refereed)
    Abstract [en]

    During summer of 2004, about 2.7 million hectare of boreal forest burned in Alaska, the largest annual area burned on record, and another 3.1 million hectare burned in Canada. This study explores the impact of emissions from these fires on light absorbing aerosol concentration levels, aerosol optical depths (AOD), and albedo at the Arctic stations Barrow (Alaska), Alert (Canada), Summit (Greenland), and Zeppelin/Ny Alesund on Spitsbergen (Norway). The Lagrangian particle dispersion model FLEXPART was run backward from these sites to identify periods that were influenced by forest fire pollution plumes. It is shown that the fires led to enhanced values of particle light absorption coefficients (sigma(ap)) at all of these sites. Barrow, about 1000 km away from the fires, was affected by several fire pollution plumes, one leading to spectacularly high 3-hour mean sigma(ap) values of up to 32 Mm(-1), more than the highest values measured in Arctic Haze. AOD measurements for a wavelength of 500 nm saturated but were estimated at above 4-5 units, unprecedented in the station records. Fire plumes were transported through the atmospheric column over Summit continuously for 2 months, during which all measured AOD values were enhanced, with maxima up to 0.4-0.5 units. Equivalent black carbon concentrations at the surface at Summit were up to 600 ng m(-3) during two major episodes, and Alert saw at least one event with enhanced sigma(ap) values. FLEXPART results show that Zeppelin was located in a relatively unaffected part of the Arctic. Nevertheless, there was a 4-day period with daily mean sigma(ap) > 0.3 Mm(-1), the strongest episode of the summer half year, and enhanced AOD values. Elevated concentrations of the highly source-specific compound levoglucosan positively confirmed that biomass burning was the source of the aerosols at Zeppelin. In summary, this paper shows that boreal forest fires can lead to elevated concentrations of light absorbing aerosols throughout the entire Arctic. Enhanced AOD values suggest a substantial impact of these plumes on radiation transmission in the Arctic atmosphere. During the passage of the largest fire plume, a pronounced drop of the albedo of the snow was observed at Summit. We suggest that this is due to the deposition of light absorbing particles on the snow, with further potentially important consequences for the Arctic radiation budget.

  • 23. Tingley, Martin P.
    et al.
    Huybers, Peter
    Heterogeneous warming of Northern Hemisphere surface temperatures over the last 1200 years2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 9, p. 4040-4056Article in journal (Refereed)
    Abstract [en]

    The relationship between the mean and spatial variability of Northern Hemisphere surface temperature anomalies over the last 1200 years is examined using instrumental and proxy records. Nonparametric statistical tests applied to 14 well-studied, annually resolved proxy records identify two centuries roughly spanning the Medieval Climate Anomaly as characterized by increased spatial variability relative to the preinstrumental baseline climate, whereas two centuries spanning the Little Ice Age are characterized by decreased spatial variability. Analysis of the instrumental record similarly indicates that the late and middle twentieth century warm intervals are generally associated with increased spatial variability. In both proxy and instrumental records an overall relationship between the first two moments is identified as a weak but significant positive correlation between time series of the spatial mean and spatial standard deviation of temperature anomalies, indicating that warm and cold anomalies are respectively associated with increased and reduced spatial variability. Insomuch as these historical patterns of relatively heterogeneous warming as compared with cooling hold, they suggest that future warming will feature increased regional variability.

  • 24. Tomasi, C.
    et al.
    Vitale, V.
    Lupi, A.
    Di Carmine, C.
    Campanelli, M.
    Herber, A.
    Treffeisen, R.
    Stone, R. S.
    Andrews, E.
    Sharma, S.
    Radionov, V.
    von Hoyningen-Huene, W.
    Stebel, K.
    Hansen, G. H.
    Myhre, C. L.
    Wehrli, C.
    Aaltonen, V.
    Lihavainen, H.
    Virkkula, A.
    Hillamo, R.
    Ström, J.
    Toledano, C.
    Cachorro, V. E.
    Ortiz, P.
    de Frutos, A. M.
    Blindheim, S.
    Frioud, M.
    Gausa, M.
    Zielinski, T.
    Petelski, T.
    Yamanouchi, T.
    Aerosols in polar regions: A historical overview based on optical depth and in situ observations2007In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 112, no D16, article id D16205Article, review/survey (Refereed)
    Abstract [en]

    Large sets of filtered actinometer, filtered pyrheliometer and Sun photometer measurements have been carried out over the past 30 years by various groups at different Arctic and Antarctic sites and for different time periods. They were examined to estimate ensemble average, long-term trends of the summer background aerosol optical depth AOD(500 nm) in the polar regions ( omitting the data influenced by Arctic haze and volcanic eruptions). The trend for the Arctic was estimated to be between -1.6% and -2.0% per year over 30 years, depending on location. No significant trend was observed for Antarctica. The time patterns of AOD( 500 nm) and angstrom ngstrom's parameters a and beta measured with Sun photometers during the last 20 years at various Arctic and Antarctic sites are also presented. They give a measure of the large variations of these parameters due to El Chichon, Pinatubo, and Cerro Hudson volcanic particles, Arctic haze episodes most frequent in winter and spring, and the transport of Asian dust and boreal smokes to the Arctic region. Evidence is also shown of marked differences between the aerosol optical parameters measured at coastal and high-altitude sites in Antarctica. In situ optical and chemical composition parameters of aerosol particles measured at Arctic and Antarctic sites are also examined to achieve more complete information on the multimodal size distribution shape parameters and their radiative properties. A characterization of aerosol radiative parameters is also defined by plotting the daily mean values of a as a function of AOD( 500 nm), separately for the two polar regions, allowing the identification of different clusters related to fifteen aerosol classes, for which the spectral values of complex refractive index and single scattering albedo were evaluated.

  • 25. Treffeisen, R. E.
    et al.
    Thomason, L. W.
    Ström, J.
    Herber, A. B.
    Burton, S. P.
    Yamanouchi, T.
    Stratospheric Aerosol and Gas Experiment (SAGE) II and III aerosol extinction measurements in the Arctic middle and upper troposphere2006In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 111, no D17, article id D17203Article in journal (Refereed)
    Abstract [en]

    In recent years, substantial effort has been expended toward understanding the impact of tropospheric aerosols on Arctic climate and chemistry. A significant part of this effort has been the collection and documentation of extensive aerosol physical and optical property data sets. However, the data sets present significant interpretive challenges because of the diverse nature of these measurements. Among the longest continuous records is that by the spaceborne Stratospheric Aerosol and Gas Experiment (SAGE) II. Although SAGE tropospheric measurements are restricted to the middle and upper troposphere, they may be able to provide significant insight into the nature and variability of tropospheric aerosol, particularly when combined with ground and airborne observations. This paper demonstrates the capacity of aerosol products from SAGE II and its follow-on experiment SAGE III to describe the temporal and vertical variations of Arctic aerosol characteristics. We find that the measurements from both instruments are consistent enough to be combined. Using this combined data set, we detect a clear annual cycle in the aerosol extinction for the middle and upper Arctic troposphere.

  • 26.
    Vega, C. P.
    et al.
    Uppsala Univ, Dept Earth Sci, Uppsala, Sweden..
    Pohjola, V. A.
    Uppsala Univ, Dept Earth Sci, Uppsala, Sweden..
    Samyn, D.
    Uppsala Univ, Dept Earth Sci, Uppsala, Sweden..
    Pettersson, R.
    Uppsala Univ, Dept Earth Sci, Uppsala, Sweden..
    Isaksson, E.
    Norwegian Polar Res Inst, Tromso, Norway..
    Bjorkman, M. P.
    Norwegian Polar Res Inst, Tromso, Norway..
    Martma, T.
    Tallinn Univ Technol, Inst Geol, EE-19086 Tallinn, Estonia..
    Marca, A.
    Univ E Anglia, Sch Environm Sci, Norwich NR4 7TJ, Norfolk, England..
    Kaiser, J.
    Univ E Anglia, Sch Environm Sci, Norwich NR4 7TJ, Norfolk, England..
    First ice core records of NO3- stable isotopes from Lomonosovfonna, Svalbard2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 1, p. 313-330Article in journal (Refereed)
    Abstract [en]

    Samples from two ice cores drilled at Lomonosovfonna, Svalbard, covering the period 1957-2009, and 1650-1995, respectively, were analyzed for NO(3)(-)concentrations, and NO3- stable isotopes (N-15 and O-18). Post-1950 N-15 has an average of (-6.91.9), which is lower than the isotopic signal known for Summit, Greenland but agrees with values observed in recent Svalbard snow and aerosol. Pre-1900 N-15 has an average of (4.21.6)parts per thousand suggesting that natural sources, enriched in the N-15 isotope, dominated before industrialization. The post-1950 O-18 average of (75.1 +/- 4.1)parts per thousand agrees with data from low and polar latitudes, suggesting similar atmospheric NOy (NOy=NO+NO2+HNO3) processing pathways. The combination of anthropogenic source N-15 and transport isotope effect was estimated as -29.1 parts per thousand for the last 60years. This value is below the usual range of NOx (NOx=NO+NO2) anthropogenic sources which is likely the result of a transport isotope effect of -32 parts per thousand. We suggest that the N-15 recorded at Lomonosovfonna is influenced mainly by fossil fuel combustion, soil emissions, and forest fires; the first and second being responsible for the marked decrease in N-15 observed in the post-1950s record with soil emissions being associated to the decreasing trend in N-15 observed up to present time, and the third being responsible for the sharp increase of N-15 around 2000. Key Points

  • 27. Zhou, J C
    et al.
    Swietlicki, E
    Berg, O H
    Aalto, P P
    Hameri, K
    Nilsson, E D
    Leck, C
    Hygroscopic properties of aerosol particles over the central Arctic Ocean during summer2001In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 106, no D23, p. 32111-32123Article in journal (Refereed)
    Abstract [en]

    The hygroscopic properties of submicrometer aerosol particles in the Arctic summer marine boundary layer (MBL) were observed on board the icebreaker Oden during the Arctic Ocean Expedition 1996 (AOE-96). The measurements were performed between July 15 and August 25 1996 and covered the region between longitudes 16degrees-147degreesE and latitudes 70degrees-87.5degreesN, mostly over melting pack ice. The hygroscopic tandem differential mobility analyzer (H-TDMA) was used to determine the hygroscopic diameter growth of aerosol particles at four dry diameters (15, 35, 50, and 165 nm) and three relative humidities (50%, 70%, and 90% RH). The hygroscopic behavior of the aerosol particles over the pack ice showed large temporal variations, in contrast to previous observations in marine boundary layers over warmer oceans. These variations were mostly due to the high degree of vertical atmospheric stratification often observed over the pack ice. However, when comparing the average diameter growth factors of the more hygroscopic particle group, representing an aged aerosol with growth factors between 1.4-1.9 at 90% RH and present in 81-86% of all cases, the agreement between the measurements over the Arctic and the warmer oceans was very good and depended on the average wind speed. The average diameter growth factors of the more hygroscopic particles as a function of relative humidity were modeled empirically by power law expressions. The concentration of cloud condensation nuclei (CCN) estimated from aerosol number size distribution and hygroscopic growth data correlated well with direct measurements but overpredicted the CCN concentrations by about 30%. In 43 cases when the sampled air mass had undergone processing in Arctic Ocean MBL clouds, the minimum CCN diameter was estimated to be 76 +/- 15 nm, corresponding to effective water vapor supersaturations of 0.28 +/- 0.08%.

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