Snow Concentration Research Articles

Formation of glacier runoff on the northern slope of Tavan Bogd mountain massif based on stable isotopes data

This investigation is based on measurements of stable isotopes concentrations (δD and δ18О) in water, snow and ice samples. Glaciers are composed of ice, snow, and fi n of atmospheric origin. The isotopic composition of these components is different, so when melting they form the melted glacial water with different isotope characteristics. Summer precipitation contains the heaviest isotopes, but only a small part of them remains on the glacier. The average isotopic composition of glacier ice represents the average composition of precipitation that accumulates on it. However, snow and fi n of different seasons can occur on the glacier surface, the isotopic composition of which differs from the isotopic composition of glacier ice. At different times of the ablation season different parts of the glacier melt, therefore the isotopic composition of melt waters will be different. Differences in the isotopic composition of the major runoff-forming components on the Northern slopes of the massif Tabyn-Bogdo-Ola had been identified. A part of melting ice in the formation of the runoff on this massif is determined by estimation of the isotopic composition of snow, ice, and fi n on different glaciers of this region. The average δ18О of snow on the glacier surface is −11.9‰, and this snow can be attributed to the precipitation fallen in late spring or early summer. Measured average isotopic composition of precipitation (δ18О = −11.9‰) was compared with the online calculator of the isotope content in precipitation (OIPC). The isotopic composition of glacial melt waters on the Northern macro-slope in the middle of July 2015 (δ18О = −15.3‰) differs from the isotopic composition of the territory of the Mongolian part of the massif (δ18О = −17.4‰) obtained from results of the analysis of eight samples taken at different edges of the glaciers at the beginning of August 2013. Isotopic separation shows important role of summer snow in feeding the glacial rivers of the massif even in the middle of the ablation season, especially for glaciers in the central part of the massif. The role of seasonal snow in feeding the glacier streams depends on the morphological type of glacier. It is maximum for corrie glaciers and minimum for the valley ones.

CFD simulation of snow transport over flat, uniformly rough, open terrain: Impact of physical and computational parameters

In the past, computational fluid dynamics (CFD) simulations have been successfully applied for the prediction of snow drift around buildings and on building roofs. A literature study indicates that a wide range of influential computational and physical parameters exist for snow drifting predictions in CFD, while the impact of these parameters is unclear, resulting in a lack of available CFD simulation guidelines. Therefore, this study presents a systematic and generic analysis with emphasis on the fundamentals of snow transport prediction techniques. Snow transport over flat, uniformly rough, open terrain, including snow saltation and snow suspension is successfully simulated using CFD and the results are compared to field measurements of snow concentrations for validation. This paper investigates the impact of grid resolution, falling velocity of snow, turbulent Schmidt number, threshold friction velocity of snow and turbulence model on the CFD simulation results. The results show that the falling velocity and the turbulent Schmidt number have the largest impact. A slight change in the falling velocity or the turbulent Schmidt number significantly impacts the predicted snow concentration in the air. In addition, the turbulence model mainly affects the turbulent kinetic energy, another key factor that influences the numerical predictions of snow transport.

Impact of bogie cavity shapes and operational environment on snow accumulating on the bogies of high-speed trains

In this paper, the snow accumulation on the bogies of high-speed trains has been investigated using a numerical simulation method based on the unsteady Reynolds-Averaged Navier-Stokes simulations (URANS) coupled with the Discrete Phase Model (DPM). The effects of bogie cut outs’ shape, running speed of high-speed trains and snow particle density and diameter on the snow accumulation and particle movement characteristics are discussed. The results show that the bogie installation region with inclined plates shows better anti-snow performance than the configuration with straight plates, which greatly affects the flow structure and snow concentration distribution in the upper space of bogie regions. The running speed of high-speed trains has dominant effect on the snow accumulation on the bogies, and the snow accumulation issue of bogie becomes more serious with increasing running speed. Furthermore, the snow particle density and diameter also have large influence on the snow accumulation on the bogies. With the increase of snow particle density and diameter, the flow range at height direction around bogie region of snow particles become lower and the quality of snow accumulation decrease significantly.

Dissolved organic carbon fractionation accelerates glacier-melting: A case study in the northern Tibetan Plateau

In glacierized regions, melting process has a significant effect on concentrations and light absorption characteristics of dissolved organic carbon (DOC), potentially resulting in variations of its radiative forcing, which is not yet relevant research at glacier region of the Tibetan Plateau (TP). In this study, DOC fractionation and its radiative forcing change during the melting process were investigated at Laohugou glacier No. 12 (LHG glacier) in western Qilian Mts., northern TP. DOC concentrations in fresh snow, snowpit and surface ice samples were 0.38 ± 0.06, 0.22 ± 0.11 and 0.60 ± 0.21 mg L−1, respectively. Their mass absorption cross-section at 365 nm (MAC365) were 0.65 ± 0.16, 4.71 ± 3.68 and 1.44 ± 0.52 m2 g−1, respectively. The MAC365 values of snowpit samples showed a significant negative correlation with DOC concentrations, indicating DOC with high MAC365 values were likely to be kept in snow during the melting process. Topsoil samples of LHG glacierized region likely contributed a lot to snowpit DOC with high MAC365 values due to their similar absorption spectra. Spatially, the DOC concentration of surface ice samples increased from terminus to the upper part of the glacier. Correspondingly, the MAC365 value showed decreased trend. In the freezing experiment on surface ice and topsoil samples, small part of DOC with high MAC365 value was also likely to enter first frozen solid phase. In addition, the radiative forcing caused by snowpit and surface ice DOC increased around 7.64 ± 2.93 and 4.95 ± 1.19 times relative to fresh snow DOC, indicating the snow/ice melting caused by increased light-absorbing DOC needs to be considered in the future research.

Scale Interactions in Turbulence for Mountain Blowing Snow

Abstract Blowing snow particle transport responds to wind motions across many length and time scales. This coupling is nonlinear by nature and complicated in atmospheric flows where eddies of many sizes are superimposed. In mountainous terrain, wind flow descriptions are further complicated by topographically influenced or enhanced flows. To improve the current understanding and modeling of blowing snow transport in complex terrain, statistically significant timing and frequencies of wind–snow coupling were identified in high-frequency observations of surface blowing snow and near-surface turbulence from a mountain field site in the Canadian Rockies. Investigation of the mechanisms influencing near-surface, high-frequency turbulence and snow concentration fluctuations provided strong evidence for amplitude modulation from large-scale motions. The large-scale atmospheric motions modulating near-surface turbulence and snow transport were then compared to specific quadrant analysis structures recently identified as relevant for outdoor blowing snow transport. The results suggest that large atmospheric structures modulate the amplitude of high-frequency turbulence and modify turbulence statistics typically used to model blowing snow. Additionally, blowing snow was preferentially redistributed under the footprint of these same sweep motions, with both low- and high-frequency coherence increasing in their presence.

Origin of elemental carbon in snow from western Siberia and northwestern European Russia during winter–spring 2014, 2015 and 2016

Abstract. Short-lived climate forcers have been proven important both for the climate and human health. In particular, black carbon (BC) is an important climate forcer both as an aerosol and when deposited on snow and ice surface because of its strong light absorption. This paper presents measurements of elemental carbon (EC; a measurement-based definition of BC) in snow collected from western Siberia and northwestern European Russia during 2014, 2015 and 2016. The Russian Arctic is of great interest to the scientific community due to the large uncertainty of emission sources there. We have determined the major contributing sources of BC in snow in western Siberia and northwestern European Russia using a Lagrangian atmospheric transport model. For the first time, we use a recently developed feature that calculates deposition in backward (so-called retroplume) simulations allowing estimation of the specific locations of sources that contribute to the deposited mass. EC concentrations in snow from western Siberia and northwestern European Russia were highly variable depending on the sampling location. Modelled BC and measured EC were moderately correlated (R=0.53–0.83) and a systematic region-specific model underestimation was found. The model underestimated observations by 42 % (RMSE = 49 ng g−1) in 2014, 48 % (RMSE = 37 ng g−1) in 2015 and 27 % (RMSE = 43 ng g−1) in 2016. For EC sampled in northwestern European Russia the underestimation by the model was smaller (fractional bias, FB > −100 %). In this region, the major sources were transportation activities and domestic combustion in Finland. When sampling shifted to western Siberia, the model underestimation was more significant (FB < −100 %). There, the sources included emissions from gas flaring as a major contributor to snow BC. The accuracy of the model calculations was also evaluated using two independent datasets of BC measurements in snow covering the entire Arctic. The model underestimated BC concentrations in snow especially for samples collected in springtime.

Feedback mechanisms between snow and atmospheric mercury: Results and observations from field campaigns on the Antarctic plateau

The Antarctic Plateau snowpack is an important environment for the mercury geochemical cycle. We have extensively characterized and compared the changes in surface snow and atmospheric mercury concentrations that occur at Dome C. Three summer sampling campaigns were conducted between 2013 and 2016.The three campaigns had different meteorological conditions that significantly affected mercury deposition processes and its abundance in surface snow. In the absence of snow deposition events, the surface mercury concentration remained stable with narrow oscillations, while an increase in precipitation results in a higher mercury variability. The Hg concentrations detected confirm that snowfall can act as a mercury atmospheric scavenger. A high temporal resolution sampling experiment showed that surface concentration changes are connected with the diurnal solar radiation cycle. Mercury in surface snow is highly dynamic and it could decrease by up to 90% within 4/6 h. A negative relationship between surface snow mercury and atmospheric concentrations has been detected suggesting a mutual dynamic exchange between these two environments.Mercury concentrations were also compared with the Br concentrations in surface and deeper snow, results suggest that Br could have an active role in Hg deposition, particularly when air masses are from coastal areas.This research presents new information on the presence of Hg in surface and deeper snow layers, improving our understanding of atmospheric Hg deposition to the snow surface and the possible role of re-emission on the atmospheric Hg concentration.

Distributions and light absorption property of water soluble organic carbon in a typical temperate glacier, southeastern Tibetan Plateau

Water-soluble organic carbon (WSOC) widely stored in glaciers from local and distant sources, and then released it to downstream environments under a warming climate. Climatic driven changes to glacial run-off are larger and represent an important flux of organic carbon. However, very few WSOC data are currently available to fully characterize WSOC variation in the temperate glacierized regions of the Tibetan Plateau (TP). This study first systematically evaluated the concentration characteristics and light absorbing property of WSOC, and insoluble particulate carbon (IPC) in snow and ice of a typical temperate glacier on Mt. Yulong. Average concentrations of WSOC were 0.61 ± 0.21 mg L−1 in Baishui glacier on Mt. Yulong. WSOC concentrations in surface aged snow were dramatically decreased with the time extension during the entire monsoon season due to extensive glacial melting and scavenging effects by meltwater.The MAC values of WSOC calculated at 365 nm was 6.31 ± 0.34 m2 g−1 on Mt. Yulong, and there exists distinct spectral dependence of MACwsoc within the wavelength range (260 – 700 nm). The low AAE330–400 values suggest the light absorption of WSOC is more spectrally neutral. The flux of WSOC in Baishui glacier was 0.99 gC m−2 yr−1, while the IPC flux was 4.77 gC m−2 yr−1. Total WSOC storage in the Baishui glacier was estimated to be 1.5 tone C and total IPC storage was 7.25 tone C (1 tone = 106 g). Moreover, glacial melting was reinforced by the soluble and insoluble light absorbing impurities (ILAIs) in glaciers, Baishui glacier can be considered as a fraction of carbon source under the scenario of a warming climate, more importantly, WSOC in snow and ice needs to be taken into account in calculating the radiative forcing of ILAIs and accelerating glacial melting.

Meltwater from snow contaminated by oil sands emissions is toxic to larval fish, but not spring river water

To assess the toxicity of winter-time atmospheric deposition in the oil sands mining area of Northern Alberta, embryo-larval fathead minnow (Pimephales promelas) were exposed to snowmelt samples. Snow was collected in 2011–2014 near (<7km) oil sands open pit mining operations in the Athabasca River watershed and at sites far from (>25km) oil sands mining. Snow was shipped frozen back to the laboratory, melted, and amended with essential ions prior to testing. Fertilized fathead minnow eggs were exposed (<24h post-fertilization to 7–16days post-hatch) to a range of 25%–100% snowmelt. Snow samples far from (25–277km away) surface mining operations and upgrading facilities did not affect larval fathead minnow survival at 100%. Snow samples from sites near surface mining and refining activities (<7km) showed reduced larval minnow survival. There was some variability in the potencies of snow year-to-year from 2011 to 2014, and there were increases in deformities in minnows exposed to snow from 1 site on the Steepbank River. Although exposure to snowmelt from sites near oil sands surface mining operations caused effects in larval fish, spring melt water from these same sites in late March–May of 2010, 2013 and 2014 showed no effects on larval survival when tested at 100%. Snow was analyzed for metals, total naphthenic acid concentrations, parent PAHs and alkylated PAHs. Naphthenic acid concentrations in snow were below those known to affect fish larvae. Concentrations of metals in ion-amended snow were below published water quality guideline concentrations. Compared to other sites, the snowmelt samples collected close to mining and upgrading activities had higher concentrations of PAHs and alkylated PAHs associated with airborne deposition of fugitive dusts from mining and coke piles, and in aerosols and particles from stack emissions. CapsuleSnow collected close to oil sands surface mining sites is toxic to larval fathead minnows in the lab; however spring melt water samples from the same sites do not reduce larval fish survival.

Numerical Simulation of Snow Accumulation on a Bogie of a High-Speed Train

The operation of high-speed trains in ice and snow weather results in a large amount of snow accumulation with ice on bogie, which will seriously damage the safety of high-speed trains. In this paper, the snow accumulation on the bogie has been investigated using numerical simulation method based on Realizable k  turbulence model. The accuracy of mesh resolution and methodology of CFD were validated by combining with the experimental results of wind tunnel tests. The Discrete Phase Model (DPM) was used to investigate the process of snow accumulation on bogie. The results show that the high-concentration snow particles mainly flow under the bogie, and the heat-producing equipment is in high snow concentration while the top surfaces of bogie are in low one; when high-speed trains running in one way, the snow on the front motor and gear cover is more than the rear, while the snow accumulation on the rear brake calipers is more than the front, the accumulation quality of snow on the motors is far more than on brake calipers and gear covers.

Pharmaceuticals and other anthropogenic chemicals in atmospheric particulates and precipitation

Air and precipitation samples were analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS) and gas chromatography mass spectrometry (GC–MS) for pharmaceuticals, personal care products, and other commercial chemicals within the St. Paul/Minneapolis metropolitan area of Minnesota, U.S. Of the 126 chemicals analyzed, 17 were detected at least once. Bisphenol A, N,N-diethyl-meta-toluamide (DEET), and cocaine were the most frequently detected; their maximum concentrations in snow were 3.80, 9.49, and 0.171ng/L and in air were 0.137, 0.370, and 0.033ng/m3, respectively. DEET and cocaine were present in samples of rain up to 14.5 and 0.806ng/L, respectively. Four antibiotics - ofloxacin, ciprofloxacin, enrofloxacin, and sulfamethoxazole - were detected at concentrations up to 10.3ng/L in precipitation, while ofloxacin was the sole antibiotic detected in air at 0.013ng/m3. The X-ray contrast agent iopamidol and the non-steroidal anti-inflammatory drug naproxen were detected in snow up to 228ng/L and 3.74ng/L, respectively, while caffeine was detected only in air at 0.069 and 0.111ng/m3. Benzothiazole was present in rain up to 70ng/L, while derivatives of benzotriazole – 4-methylbenzotriazole, 5-methylbenzotriazole, and 5-chlorobenzotriazole - were detected at concentrations up to 1.5ng/L in rain and 3.4ng/L in snow. Nonylphenol and nonylphenol monoethoxylate were detected once in air at 0.165 and 0.032ng/m3, respectively. Although the sources of these chemicals to atmosphere are not known, fugacity analysis suggests that wastewater may be a source of nonylphenol, nonylphenol monoethoxylate, DEET, and caffeine to atmosphere. The land-spreading of biosolids is known to generate PM10 that could also account for the presence of these contaminants in air. Micro-pollutant detections in air and precipitation are similar to the profile of contaminants reported previously for surface water. This proof of concept study suggests that atmospheric transport of these chemicals may partially explain the ubiquity of these contaminants in the aquatic environment.

Spring Melt and the Redistribution of Organochlorine Pesticides in the Sea-Ice Environment: A Comparative Study between Arctic and Antarctic Regions.

Complementary sampling of air, snow, sea-ice, and seawater for a range of organochlorine pesticides (OCPs) was undertaken through the early stages of respective spring sea-ice melting at coastal sites in northeast Greenland and eastern Antarctica to investigate OCP concentrations and redistribution during this time. Mean concentrations in seawater, sea-ice and snow were generally greater at the Arctic site. For example, α-HCH was found to have the largest concentrations of all analytes in Arctic seawater and sea-ice meltwater samples (224-253 and 34.7-48.2 pg·L-1 respectively compared to 1.0-1.3 and <0.63 pg·L-1 respectively for Antarctic samples). Differences in atmospheric samples were generally not as pronounced however. Findings suggest that sea-ice OCP burdens originate from both snow and seawater. The distribution profile between seawater and sea-ice showed a compound-dependency for Arctic samples not evident with those from the Antarctic, possibly due to full submersion of sea-ice at the former. Seasonal sea-ice melt processes may alter the exchange rates of selected OCPs between air and seawater, but are not expected to reverse their direction, which fugacity modeling indicates is volatilisation in the Arctic and net deposition in the Antarctic. These predictions are consistent with the limited current observations.

Distribution of light-absorbing impurities in snow of glacier on Mt. Yulong, southeastern Tibetan Plateau

Insoluble light-absorbing impurities (ILAIs) in surface snow of glacier reduce snow albedo and accelerate glacier melt. In order to assess effects of ILAIs on glacier melt, we present the first results from field measurements of ILAIs, including black carbon (BC) and dust in snowpacks of glacier on Mt. Yulong, southeastern Tibetan Plateau (TP). Amplification factors because of snow melt were calculated for BC and dust concentrations in surface snow, and melt scavenging rates, effects of ILAIs on snow spectral albedo, and associated radiative forcing (RF) were estimated. Melt amplification generally appeared to be confined to the top few centimeters of the snowpack, and our results indicated that BC was more efficiently scavenged with meltwater than the other insoluble light-absorbers (e.g., dust). Absorbing impurities reduced snow spectral albedo more with larger particulate grain radius (re). Spectral albedo reduction was investigated using the SNow ICe Aerosol Radiative (SNICAR) model. Albedo reduction for 1200ngg−1 of BC in Mt. Yulong snow was 0.075 for snow with re=500 compared with re=200μm. If dust (51.37ppm) was the only impurity in the snowpack, the spectral albedo reduction would be only 0.03, and the associated RF was 42.76Wm−2. For a BC and dust mixed scenario, the spectral albedo was substantially reduced (0.11±0.03), and the associated RF (145.23Wm−2) was more than three times larger than that for the dust-only scenario. BC in snow is an active factor controlling snow albedo and snow-ice RF. Further observational studies are needed to quantify the contribution of BC and dust to albedo reduction and glacier melt and to characterize the variation of glacier RF.

Effects of the Wegener–Bergeron–Findeisen process on global black carbon distribution

Abstract. We systematically investigate the effects of Wegener–Bergeron–Findeisen process (hereafter WBF) on black carbon (BC) scavenging efficiency, surface BCair, deposition flux, concentration in snow (BCsnow, ng g−1), and washout ratio using a global 3-D chemical transport model (GEOS-Chem). We differentiate riming- versus WBF-dominated in-cloud scavenging based on liquid water content (LWC) and temperature. Specifically, we implement an implied WBF parameterization using either temperature or ice mass fraction (IMF) in mixed-phase clouds based on field measurements. We find that at Jungfraujoch, Switzerland, and Abisko, Sweden, where WBF dominates in-cloud scavenging, including the WBF effect strongly reduces the discrepancies of simulated BC scavenging efficiency and washout ratio against observations (from a factor of 3 to 10 % and from a factor of 4–5 to a factor of 2). However, at Zeppelin, Norway, where riming dominates, simulation of BC scavenging efficiency, BCair, and washout ratio become worse (relative to observations) when WBF is included. There is thus an urgent need for extensive observations to distinguish and characterize riming- versus WBF-dominated aerosol scavenging in mixed-phase clouds and the associated BC scavenging efficiency. Our model results show that including the WBF effect lowers global BC scavenging efficiency, with a higher reduction at higher latitudes (8 % in the tropics and up to 76 % in the Arctic). The resulting annual mean BCair increases by up to 156 % at high altitudes and at northern high latitudes because of lower temperature and higher IMF. Overall, WBF halves the model–observation discrepancy (from −65 to −30 %) of BCair across North America, Europe, China and the Arctic. Globally WBF increases BC burden from 0.22 to 0.29–0.35 mg m−2 yr−1, which partially explains the gap between observed and previous model-simulated BC burdens over land. In addition, WBF significantly increases BC lifetime from 5.7 to ∼ 8 days. Additionally, WBF results in a significant redistribution of BC deposition in source and remote regions. Specifically, it lowers BC wet deposition (by 37–63 % at northern mid-latitudes and by 21–29 % in the Arctic), while it increases dry deposition (by 3–16 % at mid-latitudes and by 81–159 % in the Arctic). The resulting total BC deposition is lower at mid-latitudes (by 12–34 %) but higher in the Arctic (by 2–29 %). We find that WBF decreases BCsnow at mid-latitudes (by ∼ 15 %) but increases it in the Arctic (by 26 %) while improving model comparisons with observations. In addition, WBF dramatically reduces the model–observation discrepancy of washout ratios in winter (from a factor of 16 to 4). The remaining discrepancies in BCair, BCsnow and BC washout ratios suggest that in-cloud removal in mixed-phased clouds is likely still excessive over land.

Organophosphate Esters in Air, Snow, and Seawater in the North Atlantic and the Arctic.

The concentrations of eight organophosphate esters (OPEs) have been investigated in air, snow and seawater samples collected during the cruise of ARK-XXVIII/2 from sixth June to third July 2014 across the North Atlantic and the Arctic. The sum of gaseous and particle concentrations (ΣOPE) ranged from 35 to 343 pg/m3. The three chlorinated OPEs accounted for 88 ± 5% of the ΣOPE. The most abundant OPE was tris(2-chloroethyl) phosphate (TCEP), with concentrations ranging from 30 to 227 pg/m3, followed by three major OPEs, such as tris(1-chloro-2-propyl) phosphate (TCPP, 0.8 to 82 pg/m3), tri-n-butyl phosphate (TnBP, 2 to 19 pg/m3), and tri-iso-butyl phosphate (TiBP, 0.3 to 14 pg/m3). The ΣOPE concentrations in snow and seawater ranged from 4356 to 10561 pg/L and from 348 to 8396 pg/L, respectively. The atmospheric particle-bound dry depositions of TCEP ranged from 2 to 12 ng/m2/day. The air-seawater gas exchange fluxes were dominated by net volatilization from seawater to air for TCEP (mean, 146 ± 239 ng/m2/day), TCPP (mean, 1670 ± 3031 ng/m2/day), TiBP (mean, 537 ± 581 ng/m2/day) and TnBP (mean, 230 ± 254 ng/m2/day). This study highlighted that OPEs are subject to long-range transport via both air and seawater from the European continent and seas to the North Atlantic and the Arctic.

Aerosol and snow transfer processes: An investigation on the behavior of water-soluble organic compounds and ionic species

The concentrations of water-soluble compounds (ions, carboxylic acids, amino acids, sugars, phenolic compounds) in aerosol and snow have been determined at the coastal Italian base “Mario Zucchelli” (Antarctica) during the 2014–2015 austral summer. The main aim of this research was to investigate the air-snow transfer processes of a number of classes of chemical compounds and investigate their potential as tracers for specific sources.The composition and particle size distribution of Antarctic aerosol was measured, and water-soluble compounds accounted for 66% of the PM10 total mass concentration. The major ions Na+, Mg2+, Cl− and SO42− made up 99% of the total water soluble compound concentration indicating that sea spray input was the main source of aerosol. These ionic species were found mainly in the coarse fraction of the aerosol resulting in enhanced deposition, as reflected by the snow composition.Biogenic sources were identified using chemical markers such as carboxylic acids, amino acids, sugars and phenolic compounds. This study describes the first characterization of amino acids and sugar concentrations in surface snow. High concentrations of amino acids were found after a snowfall event, their presence is probably due to the degradation of biological material scavenged during the snow event. Alcohol sugars increased in concentration after the snow event, suggesting a deposition of primary biological particles, such as airborne fungal spores.

Mercury and other trace metals in the seasonal snowpack across the subarctic taiga-tundra ecotone, Northwest Territories, Canada

In Canada's Northwest Territories, mining for base metals and diamonds are vital economic activities which carry risks of adverse environmental impacts. To gather baseline geochemical data against which the impact of future mining activities may be measured, a survey of trace metal concentrations in snow was carried out in 2012 along a 285-km stretch of winter mining road crossing the taiga-tundra ecotone between latitudes 62.8 and 65.5° N. The distribution of 17 elements, including mercury (Hg), was measured and mapped. Results indicate that road traffic along the winter road has only a modest impact on the metal content of the nearby tundra-taiga snowpack, and that this impact is largely due to the mobilization of soil dust and associated elements. However, some enrichment of As, Pb, Sr and Zn in snow was detected near former gold mine sites, likely reflecting the windborne dispersion of contaminated soils. The Hg concentrations in snow across the study area were generally low (≤3.01 ng L−1), and did not covary with any other metals, which suggests atmospheric deposition from distant/diffuse sources. An analysis of air back-trajectories pointed to the most likely distant (>103 km) anthropogenic source regions being eastern Asia or Russia. Using Hg data from the present survey and another source, in combination with gridded maps of snowpack water equivalent, we calculated the potential flux of atmospherically-derived Hg that could be released by spring snowmelt into the Mackenzie River to be in the order of ∼195–404 kg a−1, which may represent a substantial fraction of the estimated total Hg discharge to the Beaufort Sea.

Factors controlling black carbon distribution in the Arctic

Abstract. We investigate the sensitivity of black carbon (BC) in the Arctic, including BC concentration in snow (BCsnow, ng g−1) and surface air (BCair, ng m−3), as well as emissions, dry deposition, and wet scavenging using the global three-dimensional (3-D) chemical transport model (CTM) GEOS-Chem. We find that the model underestimates BCsnow in the Arctic by 40 % on average (median = 11.8 ng g−1). Natural gas flaring substantially increases total BC emissions in the Arctic (by ∼ 70 %). The flaring emissions lead to up to 49 % increases (0.1–8.5 ng g−1) in Arctic BCsnow, dramatically improving model comparison with observations (50 % reduction in discrepancy) near flaring source regions (the western side of the extreme north of Russia). Ample observations suggest that BC dry deposition velocities over snow and ice in current CTMs (0.03 cm s−1 in the GEOS-Chem) are too small. We apply the resistance-in-series method to compute a dry deposition velocity (vd) that varies with local meteorological and surface conditions. The resulting velocity is significantly larger and varies by a factor of 8 in the Arctic (0.03–0.24 cm s−1), which increases the fraction of dry to total BC deposition (16 to 25 %) yet leaves the total BC deposition and BCsnow in the Arctic unchanged. This is largely explained by the offsetting higher dry and lower wet deposition fluxes. Additionally, we account for the effect of the Wegener–Bergeron–Findeisen (WBF) process in mixed-phase clouds, which releases BC particles from condensed phases (water drops and ice crystals) back to the interstitial air and thereby substantially reduces the scavenging efficiency of clouds for BC (by 43–76 % in the Arctic). The resulting BCsnow is up to 80 % higher, BC loading is considerably larger (from 0.25 to 0.43 mg m−2), and BC lifetime is markedly prolonged (from 9 to 16 days) in the Arctic. Overall, flaring emissions increase BCair in the Arctic (by ∼ 20 ng m−3), the updated vd more than halves BCair (by ∼ 20 ng m−3), and the WBF effect increases BCair by 25–70 % during winter and early spring. The resulting model simulation of BCsnow is substantially improved (within 10 % of the observations) and the discrepancies of BCair are much smaller during the snow season at Barrow, Alert, and Summit (from −67–−47 % to −46–3 %). Our results point toward an urgent need for better characterization of flaring emissions of BC (e.g., the emission factors, temporal, and spatial distribution), extensive measurements of both the dry deposition of BC over snow and ice, and the scavenging efficiency of BC in mixed-phase clouds. In addition, we find that the poorly constrained precipitation in the Arctic may introduce large uncertainties in estimating BCsnow. Doubling precipitation introduces a positive bias approximately as large as the overall effects of flaring emissions and the WBF effect; halving precipitation produces a similarly large negative bias.

Reduced perchlorate in West Antarctica snow during stratospheric ozone hole

AbstractSnowpit samples collected at the West Antarctic Ice Sheet (WAIS) Divide location in January 2013 were analysed to investigate the levels and variations of perchlorate concentrations in Antarctic snow. During 2008–12, the perchlorate concentration in WAIS Divide snow ranged between 6–180 ng l–1 and followed a seasonal cycle. The highest concentrations appeared in the autumn, and the lowest in winter and spring. No apparent correlation was observed between perchlorate and nitrate or chloride concentrations in snow. Since perchlorate is believed to form in the atmosphere when chlorine species are oxidized in reactions involving ozone, perchlorate concentrations were hypothesized to be high during the spring, based on the assumption that stratospheric ozone depletion enhances tropospheric perchlorate production. The data show that perchlorate concentrations in snow were sharply reduced during stratospheric ozone depletion events; the evidence, therefore, does not support the hypothesis. Instead, the results suggest a stratospheric origin of perchlorate in Antarctic snow.

Air–snow exchange of nitrate: a modelling approach to investigate physicochemical processes in surface snow at Dome C, Antarctica

Abstract. Snowpack is a multiphase (photo)chemical reactor that strongly influences the air composition in polar and snow-covered regions. Snowpack plays a special role in the nitrogen cycle, as it has been shown that nitrate undergoes numerous recycling stages (including photolysis) in the snow before being permanently buried in the ice. However, the current understanding of these physicochemical processes remains very poor. Several modelling studies have attempted to reproduce (photo)chemical reactions inside snow grains, but these have relied on strong assumptions to characterise snow reactive properties, which are not well defined. Air–snow exchange processes such as adsorption, solid-state diffusion, or co-condensation also affect snow chemical composition. Here, we present a physically based model of these processes for nitrate. Using as input a 1-year-long time series of atmospheric nitrate concentration measured at Dome C, Antarctica, our model reproduces with good agreement the nitrate measurements in the surface snow. By investigating the relative importance of the main exchange processes, this study shows that, on the one hand, the combination of bulk diffusion and co-condensation allows a good reproduction of the measurements (correlation coefficient r = 0.95), with a correct amplitude and timing of summer peak concentration of nitrate in snow. During winter, nitrate concentration in surface snow is mainly driven by thermodynamic equilibrium, whilst the peak observed in summer is explained by the kinetic process of co-condensation. On the other hand, the adsorption of nitric acid on the surface of the snow grains, constrained by an already existing parameterisation for the isotherm, fails to fit the observed variations. During winter and spring, the modelled concentration of adsorbed nitrate is respectively 2.5 and 8.3-fold higher than the measured one. A strong diurnal variation driven by the temperature cycle and a peak occurring in early spring are two other major features that do not match the measurements. This study clearly demonstrates that co-condensation is the most important process to explain nitrate incorporation in snow undergoing temperature gradient metamorphism. The parameterisation developed for this process can now be used as a foundation piece in snowpack models to predict the inter-relationship between snow physical evolution and snow nitrate chemistry.