Seasonal variation and factors influencing perchlorate in water,snow, soil and corns in Northeastern China

Seasonal variation and influencing factors of perchlorate in snow, surface soil, rain, surface water, groundwater and corn were studied. Seven hundreds and seventy samples were collected in different periods in Harbin and its vicinity, China. Perchlorate concentrations were analyzed by ion chromatography–electrospray mass spectrometry. Results indicate that fireworks and firecrackers display from the Spring Festival to the Lantern Festival (February 2, 2011–February 17, 2011) can result in the occurrence of perchlorate in surface soil and snow. Perchlorate distribution is affected by wind direction in winter. Melting snow which contained perchlorate can dissolve perchlorate in surface soil, and then perchlorate can percolate into groundwater so that perchlorate concentrations in groundwater increased in spring. Perchlorate concentrations in groundwater and surface water decrease after rainy season in summer. Groundwater samples collected in the floodplain areas of the Songhua River and the Ashi River contained higher perchlorate concentrations than that far away with the rivers. The corns have the ability to accumulate perchlorate.     

Photochemistry of phenanthrene,pyrene, and fluoranthene in ice and snow

Although polycyclic aromatic hydrocarbons (PAHs) are common pollutants in snow, there is little quantitative data about their rates of photodegradation in this environment. To begin to address this gap, we have measured the degradation kinetics of phenanthrene, pyrene, and fluoranthene on ice, as these are the most abundant PAHs in arctic snow. Frozen aqueous solutions of individual PAHs, with and without added hydrogen peroxide (HOOH) as a source of hydroxyl radical (OH), were illuminated with simulated sunlight. For all three PAHs, direct photodecay is the main mechanism of degradation, while OH-initiated indirect photodegradation is a minor sink. Rate constants (±1 SE) for direct photodegradation extrapolated to midday, surface snow conditions at Summit, Greenland on the summer solstice are 3.8 (±0.8) × 10^?5, 28 (±3) × 10^?5, and 1.4 (±0.7) × 10^?5 s^?1 for phenanthrene, pyrene, and fluoranthene, respectively. Apparent quantum efficiencies for photodegradation with simulated sunlight were 3.8 (±0.8) × 10^?3, 4.3 (±0.5) × 10^?4, and 2 (±1) × 10^?5, respectively. Calculated PAH lifetimes in surface snow under Summit conditions are 1–19 h during mid-summer, but increase to >100 days in the dark winter. While the short photodegradation lifetimes in the summer suggest that there should be no appreciable PAH levels in this season, past measurements at Summit sometimes show significant levels of these PAHs in summer surface snow. This discrepancy is likely due to differences in PAH location between lab samples (where the PAHs are probably in quasi-liquid layers) and real snow (where PAHs are likely primarily associated with particulate matter).     

Denuder measurements of gas and aerosol species above Arctic snow surfaces at Alert 2000

Gas and aerosol measurements were made during the Polar Sunrise Experiment 2000 at Alert, Nunavut (Canada), using two independent denuder/filter systems for sampling and subsequent analysis by ion chromatography. Twelve to forty-eight hour samples were taken during a winter (9–21 February 2000) and a spring (17 April–5 May 2000) campaign. During the spring campaign, samples were taken at two different heights above the snow surface to investigate concentration differences. Total particulate NO₃⁻ is the most abundant inorganic nitrogen compound during Arctic springtime (mean 137.4 ng m⁻³). The NO₃⁻ fluxes were calculated above the snow surface to help identify processes that control snow–atmosphere exchange of reactive nitrogen compounds. We suggest that the observed fluxes of coarse particle NO₃⁻ via snow deposition may contribute to the nitrogen inventory in the snow surface. Measurements of surface snow provide experimental data that constrain the contribution of dry deposition of coarse particle NO₃⁻ to <7%. Wet deposition in falling snow appears to be the major contributor to the nitrate input to the snow.     

Atmospheric mercury concentrations: measurements and profiles near snow and ice surfaces in the Canadian Arctic during Alert 2000

Gaseous elemental mercury (GEM) concentration measurements were made during the Alert 2000 campaign in Alert, Nunavut, Canada, between February and May 2000. GEM exhibits dramatic mercury depletion events (MDE) concurrently with ozone in the troposphere during the Arctic springtime. Using a cold regions pyrolysis unit, it was confirmed that GEM is converted to more reactive mercury species during the MDEs. It was determined that on average 48% of this converted GEM was recovered through pyrolysis suggesting that the remaining converted GEM is deposited on the snow surfaces. Samples collected during this campaign showed an approximate 20 fold increase in mercury concentrations in the snow from the dark to light periods. Vertical gradient air profiling experiments were conducted. In the non-depletion periods GEM was found to be invariant in the air column between surface and 1–2 m heights. During a depletion period, GEM was found to be invariant in the air column except at the surface where a noticeable increase in the GEM concentration was observed. Concurrent ozone concentration profiles showed a small gradient in the air column but a sharp decrease in ozone concentration at the surface. Other profile studies showed a 41% average GEM concentration difference between the interstitial air in the snow pack and ∼2 m above the surface suggesting that GEM is emitted from the snow pack. Further profile studies showed that during MDEs surface level GEM exhibits spikes of mercury concentrations that were over double the ambient GEM concentrations. It is thought that the solar radiation may reduce reactive mercury that is deposited on the snow surface during a MDE back to its elemental form which is then increasingly released from the snow pack as the temperature increases during the day. This is observed when wind speeds are very low.     

Seasonal and spatial trends in south Greenland snow chemistry

The spatial, temporal, source and physical controls on chloride, nitrate, sulfate and sodium in south Greenland snow are presented in this paper based on chemical data from snowpit and fresh snow samples. The snowpit samples cover the period June 1982–June 1984 and the fresh surface snow samples represent one storm event sampled over a 38-km traverse from Dye 3 to the southwest. Oxygen isotope dated records of chloride, sodium, excess sulfate and nitrate are discussed with respect to input timing and source. Notably the anthropogenic influx of excess sulfate is apparent in addition to an influx of excess sulfate that coincides with and is attributed to the arrival of the El Chichon cloud in S Greenland. The El Chichon event is also marked by highs in chloride and nitrate. Examination of fresh surface snow reveals geographic, temperature and moisture controls on deposition. Some excess sulfate close to Dye 3 can be attributed to local pollution.     

Atmospheric heavy metals in high altitude surface snows from Mont Blanc,French Alps

We present here the results of the analysis of various surface snow samples collected in the massif of Mont Blanc, French Alps, at three locations whose altitude ranges from 3560 to 4785 m a. s l. These samples were collected using ultra-clean techniques similar to the ones developed for Greenland and Antarctic studies. They were analysed for Pb, Cd, Cu, Zn, Ag, Na, Mg, K, Ca, Fe, Al and Mn by Graphite Furnace Atomic Absorption in clean room conditions. Measured concentrations are very low, then confirming the extreme purity of high altitude snow in the Alps. Principal components factor analysis of the data suggest a crustal source for Na, Mg, K, Ca, Fe, Mn and Al; heavy metals Pb, Cd, Cu, Zn and Ag are found on the other hand to be derived from one or several sources independent of the crustal source. Measured concentrations in snow appear to be closely related to thos̀e previously published by other authors for local aerosols.     

Spatial and seasonal variations of elemental composition in Mt. Everest (Qomolangma) snow/firn

In May 2005, a total of 14 surface snow (0–10 cm) samples were collected along the climbing route from the advanced base camp to the summit (6500–8844 m a.s.l.) on the northern slope of Mt. Everest (Qomolangma). A 108 m firn/ice core was retrieved from the col of the East Rongbuk Glacier (28.03°N, 86.96°E, 6518 m a.s.l.) on the north eastern saddle of Mt. Everest in September 2002. Surface snow and the upper 3.5 m firn samples from the core were analyzed for major and trace elements by inductively coupled plasma mass spectroscopy (ICP-MS). Measurements show that crustal elements dominated both surface snow and the firn core, suggesting that Everest snow chemistry is mainly influenced by crustal aerosols from local rock or prevalent spring dust storms over southern/central Asia.There are no clear trends for element variations with elevation due to local crustal aerosol inputs or redistribution of surface snow by strong winds during the spring. Seasonal variability in snow/firn elements show that high elemental concentrations occur during the non-monsoon season and low values during the monsoon season. Ca, Cr, Cs, and Sr display the most distinct seasonal variations. Elemental concentrations (especially for heavy metals) at Mt. Everest are comparable with polar sites, generally lower than in suburban areas, and far lower than in large cities. This indicates that anthropogenic activities and heavy metal pollution have little effect on the Mt. Everest atmospheric environment. Everest firn core REE concentrations are the first reported in the region and seem to be comparable with those measured in modern and Last Glacial Maximum snow/ice samples from Greenland and Antarctica, and with precipitation samples from Japan and the East China Sea. This suggests that REE concentrations measured at Everest are representative of the background atmospheric environment.     

Black carbon concentrations in precipitation and near surface air in and near Halifax,Nova Scotia

Black carbon (soot) concentrations have been measured in rain water, snow samples and near surface air at several locations in Nova Scotia, Canada. The average black carbon concentration in near surface air in summer was found to be 0.54 μg m^-3 compared to 1.74 μg m^-3 in the winter season. These values are comparable to black carbon concentrations found in other mid-size urban areas. The black carbon concentration in rain water and snow samples varied between an undetectable amount to about 20 μg kg^-1 of rain (or melt) water. The relatively low concentrations of black carbon in precipitation are attributed to extratropical cyclones that often develop off-shore to the east and south of Nova Scotia in relatively clean conditions of the marine boundary layer.     

Total and methyl mercury patterns in Arctic snow during springtime at Resolute,Nunavut, Canada

Patterns of gaseous elemental mercury (GEM) were monitored at 20 and 150 cm above the snowpack near Resolute Bay, Cornwallis Island, Nunavut, Canada near the Upper Air Station of Environment Canada (74°42′N, 94°58′W) from 7 May (day 127) to 12 June (day 163) 2003. At this time of year there was 24 h daylight but still a strong diel change in solar radiation. Daily patterns of GEM-tracked solar radiation with a lag of about 2 h and the GEM gradient between these two heights showed the direction of flux. In addition to the previously established autocatalytic reactions involving halogens where reactive gaseous mercury and fine particulate mercury result in direct deposition to the snow, both diffusion to and volatilization from the snow occurred on a regular basis. Total mercury (THg) in the snowpack increased to near 30 ng L⁻¹ following 8 d of atmospheric mercury depletion then decreased to values near 1 ng L⁻¹. Losses from the snow could not be accounted for in melt water as stream runoff values were also low. In other words, most of the mercury associated with increased levels in snow was volatilized back to the atmosphere either directly from the snow or from the water surfaces. However, using accepted mass transport coefficients, the flux appeared low and other mechanisms are suggested. In contrast to THg, methyl mercury (MeHg) in the snow reached values near 140 pg L⁻¹ but also declined to less than detection limit (10 pg L⁻¹) with the onset of warmer temperatures. MeHg in stream runoff water was similar to maximal values seen in the snow. This observation is consistent with the view that MeHg came in the snowfall or was deposited to the snow pack rather than produced in the snow. In contrast, much of the THg associated with mercury depletion events was volatilized back to the atmosphere.     

Spatiotemporal variability in surface energy balance across tundra,snow and ice in Greenland

The surface energy balance (SEB) is essential for understanding the coupled cryosphere–atmosphere system in the Arctic. In this study, we investigate the spatiotemporal variability in SEB across tundra, snow and ice. During the snow-free period, the main energy sink for ice sites is surface melt. For tundra, energy is used for sensible and latent heat flux and soil heat flux leading to permafrost thaw. Longer snow-free period increases melting of the Greenland Ice Sheet and glaciers and may promote tundra permafrost thaw. During winter, clouds have a warming effect across surface types whereas during summer clouds have a cooling effect over tundra and a warming effect over ice, reflecting the spatial variation in albedo. The complex interactions between factors affecting SEB across surface types remain a challenge for understanding current and future conditions. Extended monitoring activities coupled with modelling efforts are essential for assessing the impact of warming in the Arctic.     

Snow-to-air exchanges of mercury in an Arctic seasonal snow pack in Ny-Ålesund,Svalbard

The study of mercury (Hg) cycle in Arctic regions is a major subject of concern due to the dramatic increases of Hg concentrations in ecosystem in the last few decades. The causes of such increases are still in debate, and an important way to improve our knowledge on the subject is to study the exchanges of Hg between atmosphere and snow during springtime. We organized an international study from 10 April to 10 May 2003 in Ny-Ålesund, Svalbard, in order to assess these fluxes through measurements and derived calculations.Snow-to-air emission fluxes of Hg were measured using the flux chamber technique between ∼0 and 50 ng m⁻² h⁻¹. A peak in Gaseous Elemental Mercury (GEM) emission flux from the snow to the atmosphere has been measured just few hours after an Atmospheric Mercury Depletion Event (AMDE) recorded on 22 April 2004. Surprisingly, this peak in GEM emitted after this AMDE did not correspond to any increase in Hg concentration in snow surface. A peak in GEM flux after an AMDE was observed only for this single event but not for the four other AMDEs recorded during this spring period.In the snow pack which is seasonal and about 40 cm depth above permafrost, Hg is involved in both production and incorporation processes. The incorporation was evaluated to ∼5–40 pg m² h. Outside of AMDE periods, Hg flux from the snow surface to the atmosphere was the consequence of GEM production in the air of snow and was about ∼15–50 ng m⁻² h⁻¹, with a contribution of deeper snow layers evaluated to ∼0.3–6.5 ng m⁻² h⁻¹. The major part of GEM production is then mainly a surface phenomenon. The internal production of GEM was largely increasing when snow temperatures were close to melting, indicating a chemical process occurring in the quasi-liquid layer at the surface of snow grains.     

Observations of particle growth at a remote,Arctic site

Observations of particle size distributions suggest that particles grow significantly just above the snow surface at a remote, Arctic site. Measurements were made at Summit, Greenland (71.38°N and 31.98°W) at approximately 3200 m above sea level. No new particle formation was observed locally, but growth of ultrafine particles was identified by continuous evolution of the geometric mean diameter (GMD) during four events. The duration of the growth during events was between 24 and 115 h, and calculated event-average growth rates (GR) were 0.09, 0.30, 0.27, and 0.18 nm h^?1 during each event, respectively. Four-hour GR up to 0.96 nm h^?1 were observed. Events occurred during below- and above-average temperatures and were independent of wind direction. Correlation analysis of hourly-calculated GR suggested that particle growth was limited by the availability of photochemically produced precursor gases. Sulfuric acid played a very minor role in particle growth, which was likely dominated by condensation of organic compounds, the source of which was presumably the snow surface. The role of boundary layer dynamics is not definite, although some mixing at the surface is necessary for the observation of particle growth. Due to the potentially large geographic extent of events, observations described here may provide a link between long-range transport of mid-latitude pollutants and climate regulation in the remote Arctic.     

Rain and snow scavenging of HNO3 vapor in the atmosphere

The coefficients for the wet removal of HNO₃ vapor from the atmosphere by rain (in-cloud and below-cloud) and snow have been derived under a number of approximations. The wet removal coefficients are parametrized in terms of precipitation rate. These coefficients are intended to represent the average scavenging from large precipitation bands or frontal systems where there is widespread weakly ascending air motion. Consequently, the derived coefficients would be appropriate, on an interim basis, for inclusion into regional or mesoscale models which include the wet removal of HNO₃ vapor. These coefficients, when combined with altitude-dependent precipitation rates and vertical profiles of HNO₃ concentrations, are also useful to estimate the flux of HNO₃ to the earth's surface. The derived snow scavenging coefficients are consistent with those of recent measurements by Huebert et al. Both rain and snow scavenging coefficients are also consistent with recent observations of ionic composition in winter precipitation samples which indicated that snow removes HNO₃ vapor more efficiently than rain.     

Use and validation of novel snow samplers for hydrophobic, semi-volatile organic compounds (SVOCs)

Two novel gas-tight snow samplers (snow-can and snow-tube) are presented and the performance of the snow-can in a field trial was assessed. The methodology for the sampling, extraction and analysis of persistent organic pollutants (POPs) are detailed. These samplers allow the various components of a snow sample to be analysed separately; these included the meltwater (MW), particulate matter (GFF) and vapour in the headspace (HS). Snow samples collected on the Punta Indren glacier in the Italian Alps revealed the occurrence of polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OC). Replicate samples of the same snow type were undertaken as a test of sampling precision. Relative standard deviations (RSDs) for SigmaPCBs and SigmaPAHs were approximately 30% and approximately 35% respectively. The lowest precision was found for the particle-laden snow, notably for the heavier PCB homologues. For the chlorinated compounds, the pesticides lindane and endosulfan-I had the highest levels in snow, with mean concentrations of 402 and 103 pgl(-1) (snow meltwater) respectively. The vapour present in the headspace (HS) comprised a minor component of a collected sample for all compounds, but HS concentrations for three lighter PAHs gave good agreement with those calculated based on their dimensionless Henry's law constants. This suggests that volatilisation during melting of aged snow-can be reasonably predicted with knowledge of the temperature-dependent Henry's law constant.     

An experimental and theoretical investigation of the dry deposition of particles to snow,pine trees and artificial collectors

Submicrometer and supermicrometer ammonium sulphate particles tagged with the radioisotope ³⁵S were released upwind of natural snow, trees and artificial collectors in a large field containing micrometeorological and air monitoring equipment. At a reference height of 10 cm, the average deposition velocity for 0.7 μm diameter particles was observed to be 0.039 and 0.096 cm s⁻¹ in two experiments conducted at a wind speed of 2.7 and 2.4 m s⁻¹ under stable and unstable conditions, respectively. Supermicrometer particles having an effective diameter of 7 μm were deposited to snow at a rate of 0.16 and 0.096 cm s⁻¹ in two experiments conducted under unstable conditions at a wind speed of 2.4 m s⁻¹. Compared to snow, all artificial collectors used in this study under-collected submicrometer particles and over-collected supermicrometer particles. Individual white pine branches scavenged submicrometer particles with an average efficiency of 0.015%. Comparisons of the theoretical and observed deposition rates of submicrometer particles to snow suggest that hygroscopic growth of sulphate particles in the humid nearsurface snow layer and interception by ice needles play a role in the deposition process.     

The composition of rime ice as an indicator of the quality of winter deposition

Rime ice deposition and snow chemistry has been determined over a 4-year period on the summit of Cairngorm Mountain, NE Scotland. The direction of ice deposition reflected the dominant air mass movement over the summit. Sea salt concentrations in the rime ice were approximately 2.5 times greater than in snow deposited over the same period. Excess sulphate concentrations were double, and those of nitrate nearly four times higher. The direction of deposition influenced concentrations of excess sulphate and nitrogen species (nitrate and ammonium) in rime ice. The same directional effect was found in the snow chemistry indicating increased entrapment of pollutants, or a more polluted air mass, when it prevailed from a Southerly or Easterly direction. The potential surface reactions involving gaseous species of S and N may increase the ionic loading to the rime and reflect natural ionic enrichment of the rimed snowpack surface. Because of such phenomena, rime ice is proposed as a further indicator of winter air quality revealing important information on ionic interactions and total deposition flux measurement, especially at high altitudes.     

Photoinduced reduction of divalent mercury in ice by organic matter

Reduction of divalent mercury and subsequent emission to the atmosphere has been identified as loss process from surface snow, but its mechanism and importance are still unclear. The amount of mercury that stays in the snow pack until spring is of significance, because during snow melt it may be released to the aquatic environment and enter the food web. Better knowledge of its fate in snow might further assist the interpretation of ice core data as paleo-archive. Experiments were performed under well-controlled laboratory conditions in a coated wall flow tube at atmospheric pressure and irradiated with light between 300 nm and 420 nm. Our results show that the presence of benzophenone and of oxalic acid significantly enhances the release of mercury from the ice film during irradiation, whereas humic acid is less potent to promote the reduction. Further it was found that oxygen or chloride, and acidic conditions lowered the photolytically induced mercury release in the presence of benzophenone, while the release got larger with increasing temperatures.     

Chemical composition of fresh snow from Gulmarg, North India

The chemical composition and pH of 30 fresh snow samples collected during December 1986 to May 1987 at Gulmarg (34 degrees 03' N, 74 degrees 24' E, 2655 m above mean sea level), a remote place in north India, were studied. The snow samples were, by and large, alkaline in nature and were largely influenced by non-marine aerosols. The concentrations of cations (Ca(2+), K(+) and Mg(2+)) were more than the anions (SO(2-)(4) and NO(-)(3)). Factor analysis indicated that most of the ionic components were transported into the region during the period of measurements. The transport of ionic components could be attributed to the passage of western disturbances over this region. The comparison of concentrations of anions and cations in the snow samples at Gulmarg with those reported from a few countries in the west revealed that the composition of Gulmarg snow largely differs in the concentrations of cations rather than anions. Among the cations, the concentration of Ca(2+) was high at Gulmarg and this could be responsible for buffering the pH of snow in the alkaline range.