Characteristics of mercury exchange flux between soil and air in the heavily air-polluted area,eastern Guizhou,China

To investigate the characteristics of mercury exchange between soil and air in the heavily air-polluted area, total gaseous mercury (TGM) concentration in air and Hg exchange flux were measured in Wanshan Hg mining area (WMMA) in November, 2002 and July–August, 2004. The results showed that the average TGM concentrations in the ambient air (17.8–1101.8 ng m⁻³), average Hg emission flux (162–27827 ng m⁻² h⁻¹) and average Hg dry deposition flux (0–9434 ng m⁻² h⁻¹) in WMMA were 1–4 orders of magnitude higher than those in the background area. It is said that mercury-enriched soil is a significant Hg source of the atmosphere in WMMA. It was also found that widely distributed roasted cinnabar banks are net Hg sources of the atmosphere in WMMA. Relationships between mercury exchange flux and environmental parameters were investigated. The results indicated that the rate of mercury emission from soil could be accelerated by high total soil mercury concentration and solar irradiation. Whereas, highly elevated TGM concentrations in the ambient air can restrain Hg emission from soil and even lead to strongly atmospheric Hg deposition to soil surface. A great amount of gaseous mercury in the heavily polluted atmosphere may cycle between soil and air quickly and locally. Vegetation can inhibit mercury emission from soil and are important sinks of atmospheric mercury in heavily air-polluted area.     

Seasonal and diel variation of atmospheric mercury concentrations in the Reno (Nevada,USA) airshed

This paper describes total gaseous mercury (TGM) concentrations measured in Reno, Nevada from 2002 to 2005. The 3-year mean and median air Hg concentrations were 2.3 and 2.1 ng m⁻³, respectively. Mercury concentrations exhibited seasonality, with the highest concentrations in winter, and the lowest in summer and fall. A well-defined diel pattern in TGM concentration was observed, with maximum daily concentrations observed in the morning and minimum in the afternoon. A gradual increase of TGM concentration was observed in the evening and over night. The early morning increase in TGM was likely due to activation of local surface emission sources by rising solar irradiance and air temperature. The subsequent decline and afternoon minimum in TGM were likely related to increased vertical mixing and the buildup of atmospheric oxidants during the day resulting in increased conversion to oxidized species that are quickly deposited, coupled with weakening of the surface emissions processes. The described diel pattern was seasonally modulated with the greatest amplitude in variation of TGM concentrations occurring in the summer. It is suggested based on the comparison of diel TGM pattern with other gaseous pollutants that natural source surface emissions are a dominant source of TGM in the study area.     

Measurements of GEM fluxes and atmospheric mercury concentrations (GEM,RGM and Hgp) from an agricultural field amended with biosolids in Southern Ont., Canada (October 2004–November 2004)

Five weeks of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle bound mercury (Hg^p) concentrations as well as fluxes of GEM were measured at Maryhill, Ontario, Canada above a biosolids amended field. The study occurred during the autumn of 2004 (October–November) to capture the effects of cool weather conditions on the behaviour of mercury in the atmosphere. The initial concentration of total mercury (Hg) in the amended soil was relatively low (0.4 μg g⁻¹±10%).A micrometeorological approach was used to infer the flux of GEM using a continuous two-level sampling system with inlets at 0.40 and 1.25 m above the soil surface to measure the GEM concentration gradient. The required turbulent transfer coefficients were derived from meteorological parameters measured on site. The average GEM flux over the study was 0.1±0.2 ng m⁻² h⁻¹(±one standard deviation). The highest averaged hourly GEM fluxes occurred when the averaged net radiation was highest, although the slight diurnal patterns observed were not statistically significant for the complete flux data series. GEM emission fluxes responded to various local events including the passage of a cold front when the flux increased to 2 ng m⁻² h⁻¹ and during a biosolids application event at an adjacent field when depositional fluxes peaked at −3 ng m⁻² h⁻¹. Three substantial rain events during the study kept the surface soil moisture near field capacity and only slightly increased the GEM flux. Average concentrations of RGM (2.3±3.0 pg m⁻³), Hg^p (3.0±6.2 pg m⁻³) and GEM (1.8±0.2 ng m⁻³) remained relatively constant throughout the study except when specific local events resulted in elevated concentrations. The application of biosolids to an adjacent field produced large increases in Hg^p (25.8 pg m⁻³) and RGM (21.7 pg m⁻³) concentrations only when the wind aligned to impact the experimental equipment. Harvest events (corn) in adjacent fields also corresponded to higher concentrations of GEM and Hg^p but with no elevated peaks in RGM concentrations. Diurnal patterns were not statistically significant for RGM and Hg^p at Maryhill.     

Simultaneous measurements of total gaseous mercury at four sites on a 800 km transect: spatial distribution and short-time variability of total gaseous mercury over central Europe

Over a distance of approximately 800 km simultaneous measurements of total gaseous mercury (TGM) were performed at four sampling sites between Stockholm and Berlin. The time resolution of mercury concentration measurements was 5 min. During the sampling period from 26 June to 7 July 1995, event sampling for precipitation was carried out using bulk samplers. In addition to the mercury data, the most common meteorological and air-quality parameters were determined. Comparing the TGM background concentrations at the four sites, a weak but statistically significant south-to-north declining TGM gradient was found. From the most southern sampling site to the northern most site median values of 1.93, 1.78, 1.53 and 1.54 ng m^-3 TGM were detected. Compared with the median TGM concentration observed at the two Swedish sites, the regional background concentration near Berlin was elevated by about 25%. Whereas the 0.5 h average TGM concentration varies at the Swedish sampling sites in a very narrow range of only 0.69 ng m^-3, a much broader range of 3.28 ng m^-3 was observed at the southern sites. The increased TGM variability near Berlin was characterised by a diurnal cycle with a distinct maximum in the early morning hours (about 4:00 a.m.) before sun rise. The short time variability of the TGM concentration measured at the four sites on the south-to-north transect shows regional differences. A decreasing variability from the most southern to the most northern site became evident.     

Atmospheric mercury in the Great Smoky Mountains compared to regional and global levels

Improvements in measurement technology are permitting development of a more detailed scientific understanding of the cycling of mercury in the global atmospheric environment. Critical to advancing the state of knowledge is the acquisition of accurate measurement of speciated mercury (gaseous and particulate) at ground research stations in a variety of settings located around the globe. This paper describes one such research effort conducted at TVA's Look Rock air quality monitoring site in Tennessee—a mountain top site (813 m elevation) just west of the Great Smoky Mountains National Park. The Great Smoky Mountains National Park is the largest National Park in the eastern US and it receives environmental protection under a variety of US statutes. Gaseous and particle mercury species along with some additional trace gases were measured at Look Rock during two field studies totaling 84 days in the spring and summer of 2004. Average results for the entire sampling period are: gaseous elemental mercury Hg(0): 1.65 ng m⁻³, reactive gaseous mercury RGM: 0.005 ng m⁻³, particulate mercury Hg(p): 0.007 ng m⁻³. Literature review indicates that these levels are within the range found for other rural/remote sites in North America and worldwide. Reactive and particulate mercury comprised together less than 1%, on average, of total airborne mercury at Look Rock. When compared to the global background mercury literature, the Look Rock measurements demonstrate that the atmospheric mercury levels in the vicinity of the Great Smoky Mountains National Park are clearly dominated by the global atmospheric pool, not by local or regional sources.     

Identification,abundance and seasonal variation of anthropogenic organic aerosols from a mega-city in China

PM_2.5 aerosols were collected in Nanjing, a typical mega-city in China, during summer and winter 2004 and were characterized for aromatic and cyclic compounds using a GC/MS technique to understand the air pollution problem. They include polycyclic aromatic hydrocarbons (PAHs), hopanes, phthalates and hydroxy-PAHs (OH-PAHs). PAHs, hopanes and OH-PAHs presented higher concentrations in winter (26–178, 3.0–18, and 0.013–0.421 ng m⁻³, respectively) than in summer (12–96, 1.6–11, and 0.029–0.171 ng m⁻³, respectively) due to an enhanced coal burning for house heating and atmospheric inversion layers developed in the cold season. In contrast, phthalates are more abundant in summer (109–368 ng m⁻³, average 230 ng m⁻³) than in winter (33–390 ng m⁻³, average 170 ng m⁻³) due to an enhanced evaporation from plastics during the hot season and the subsequent deposition on the pre-existing particles. Generally, all the identified compounds showed higher concentrations in nighttime than in daytime due to inversion layers and increased emissions from heavy-duty trucks at night. PAHs, hopanes and phthalates in Nanjing aerosols are 5–100 times more abundant than those in Los Angeles, USA, indicating a serious air pollution problem in the city. Concentrations of OH-PAHs are 1–3 orders of magnitude less than their parent PAHs and comparable to those reported from other international cities. Source identification using diagnostic ratios of the organic tracers suggests that PAHs in Nanjing urban area are mainly derived from coal burning, whereas hopanes are more attributable to traffic emissions.     

The dry-deposition of speciated mercury to the Florida Everglades: Measurements and modeling

The Florida Everglades Dry-Deposition Study (FEDDS) was designed to test the viability of using new and existing measurement techniques in the estimation of the dry-depositional loading of speciated mercury (elemental gaseous, reactive gaseous and particulate) to a mixed sawgrass (Cladium jamaicense) and cattail (Typha domingensis) stand within the Florida Everglades. Measurement intensives were performed during 24 February–04 March 1999 and 05–21 June 2000, which corresponded to the climatological dry and wet seasons in South Florida, respectively. During these intensives, direct measurements of mercury dry-deposition were made using a newly developed surrogate water surface technique. These direct measurements were compared with modeled estimates of mercury dry-deposition to the site that were obtained through the use of an inferential or “bigleaf” model that was modified for use with speciated mercury. On-site measurements of ambient speciated mercury concentrations and numerous micrometeorological variables were used as input to the model.The average mercury dry-deposition measured during the 1999 FEDDS measurement intensive was 13.3±4.0 ng m⁻² day⁻¹, while the modeled deposition for this period was 3.4±2.3 ng m⁻² day⁻¹. The average mercury dry-deposition measured during the 2000 FEDDS measurement intensive was lower, 5.9±2.8 ng m⁻² day⁻¹, while the average modeled deposition for this period was 1.8±0.6 ng m⁻² day⁻¹. A least-squares linear regression suggests that the model was able to explain 74% and 73% of the variability in the datasets for the 1999 and 2000 FEDDS intensives, respectively. While reported reductions in total mercury emissions across South Florida between study periods could explain the reductions in both the measured and predicted mercury dry-deposition estimates, the increased presence of cumulus convection during the summer-intensive could have also resulted in a removal of reactive and particulate mercury species within the atmosphere of South Florida.     

The temporal distribution characteristics of total gaseous mercury at an urban monitoring site in Seoul during 1999–2000

In order to assess the temporal variabilities of atmospheric mercury (Hg) from an area moderately impacted by man-made source processes, the concentrations of total gaseous mercury were measured routinely from an urban monitoring station during January 1999–August 2000. The mean hourly concentration of Hg from overall measurements was computed to be 5.26±3.27 ng m⁻³ (N=11, 572). Using these measurement data, we inspected various aspects on the temporal distribution of Hg. When analyzed over 24 h scale, the pattern was characterized by high concentration during nighttime relative to daytime (e.g., values approaching 9 ng m⁻³). This pattern was prominent during winter and seen persistently across fall, spring, and summer. When divided seasonally, the highest mean of 6.01 ng m⁻³ was observed during winter. It appears that such wintertime dominance is most likely to come from the anthropogenic sources such as household heating systems from late fall to early spring. A close inspection of the Hg data however indicated that the seasonal variation proceeded quite dynamically. Inspection of seasonally divided data groups generally showed substantial variabilities among different months. In order to analyze the factors affecting Hg distributions over different time scale, we conducted the correlation analysis. Whereas Hg generally exhibited strong correlations with such parameters as PM, SO₂, and NO₂, its relationship varied diurnally and seasonally. The overall results of the present study suggest that changes in its source signatures can vary over varying time scale under the influence of strong man-made source processes.     

Conditional sampling for measuring mercury vapor fluxes

Surface–atmosphere mercury fluxes are difficult to measure accurately. Current techniques include dynamic flux chambers and micrometeorological gradient and aerodynamic approaches, all of which have a number of intrinsic problems associated with them. We have adapted conditional sampling (relaxed eddy accumulation), a micrometeorological technique commonly used to measure other trace gas fluxes, to measure surface–air mercury fluxes. Our initial flux measurement campaign over an agricultural soil consisted of two 1-week measurement periods, and was longer in duration than previously reported mercury flux measurement periods. Fluxes during both measurement periods ranged between 190.5 (evolution) and –91.7 ng m⁻² h⁻¹ (deposition) with an average evolution of 9.67 ng m⁻² h⁻¹. The data showed significant diurnal trends, weakly correlated with shallow soil temperatures and solar radiation. This initial trial run indicates that conditional sampling has much promise for the accurate quantification of both short and long-term mercury fluxes.     

Speciated mercury in size-fractionated particles in Shanghai ambient air

Size-fractionated particles were collected at two sites from July 2004 to April 2006 in Shanghai. The mercury in particles was extracted and divided operationally into four species: exchangeable particulate mercury (EXPM), HCl-soluble particulate mercury (HPM), elemental particulate mercury (EPM) and residual particulate mercury. The total particulate Hg concentration during the study period ranged from 0.07 ng m^?3 to 1.45 ng m^?3 with the average 0.56 ± 0.22 ng m^?3 at site 1, while 0.20 ng m^?3–0.47 ng m^?3 with the average 0.33 ± 0.09 ng m^?3 at site 2, which is far higher than some foreign cities and comparable to some cities with heavy air pollution in China. The Hg mass content also displayed evident size distribution, with higher value in PM_1.6–3.7, somewhat higher or lower than the source profile. EXAM was only found in the summer, HPM have higher percentage in summer and fall rather than in winter and spring. The different mercury species showed different correlation to temperature, relative humidity, wind speed. HPM positively depends on temperature at both sites which implies the importance of mercury transformation on particles. In foggy days TPM increased greatly, but HPM didn't vary greatly as anticipated. Instead, RPM gained a distinguished increase. It demonstrated that aqueous reaction and complex heterogenic reactions in droplet might happen in acidic environment. The correlation of mercury with other pollutants including SO₂, NO₂, CO and PM₁₀ varies with the different mercury forms. Hybrid single-particle lagrangian integrated trajectories (HYSPLIT) model was used to back trace air mass at different representative days and results indicated that transportation from Huabei Plain will increase mercury concentration in winter and fall to some extent. The possible existing compounds and their atmospheric behavior of HPM, EPM and RPM were calculated and the compared to analyze its implication on atmospheric mercury cycle.     

Atmospheric mercury measurements at Cape Point,South Africa

The monitoring of total gaseous Hg (TGM) was established at the Cape Point Global Atmospheric Watch (GAW) station in September 1995. This paper presents the first data obtained until June 1999. Atmospheric Hg concentrations were found to be fairly homogeneous fluctuating between 1.2–1.4 ng m⁻³. Whilst no significant diurnal variation is detectable, a slight seasonal variation with a TGM minimum in March–May and maximum in June–August was observed. A minimum annual TGM concentration was detected in 1997, 1 year later than observed at the Wank summit in the Northern Hemisphere (NH). The Cape Point GAW station was found to constitute a suitable site for monitoring TGM concentrations in the Southern Hemisphere (SH).     

Mercury emissions from automobiles using gasoline,diesel, and LPG

Mercury (Hg) emissions from gasoline, diesel, and liquefied petroleum gas (LPG) vehicles were measured and speciated (particulate, oxidized, and elemental mercury). First, three different fuel types were analyzed for their original Hg contents; 571.1±4.5 ng L⁻¹ for gasoline, 185.7±2.6 ng L⁻¹ for diesel, and 1230.3±23.5 ng L⁻¹ for LPG. All three vehicles were then tested at idling and driving modes. Hg in the exhaust gas was mostly in elemental form (Hg⁰), and no detectable levels of particulate (Hg^p) or oxidized (Hg²⁺) mercury were measured. At idling modes, Hg concentrations in the exhaust gas of gasoline, diesel, and LPG vehicles were 1.5–9.1, 1.6–3.5, and 10.2–18.6 ng m⁻³, respectively. At driving modes, Hg concentrations were 3.8–16.8 ng m⁻³ (gasoline), 2.8–8.5 ng m⁻³ (diesel), and 20.0–26.9 ng m⁻³ (LPG). For all three vehicles, Hg concentrations at driving modes were higher than at idling modes. Furthermore, Hg emissions from LPG vehicle was highest of all three vehicle types tested, both at idling and driving modes, as expected from the fact that it had the highest original fuel Hg content.     

Atmospheric distribution of polycyclic aromatic hydrocarbons and deposition to Galveston Bay,Texas, USA

Estimates of the atmospheric deposition to Galveston Bay of polycyclic aromatic hydrocarbons (PAHs) are made using precipitation and meteorological data that were collected continuously from 2 February 1995 to 6 August 1996 at Seabrook, TX, USA. Particulate and vapor phase PAHs in ambient air and particulate and dissolved phases in rain samples were collected and analyzed. More than 95% of atmospheric PAHs were in the vapor phase and about 73% of PAHs in the rain were in the dissolved phase. Phenanthrene and napthalene were the dominant compounds in air vapor and rain dissolved phases, respectively, while 5 and 6 ring PAH were predominant in the particulate phase of both air and rain samples. Total PAH concentrations ranged from 4 to 161 ng m⁻³ in air samples and from 50 to 312 ng l⁻¹ in rain samples. Temporal variability in total PAH air concentrations were observed, with lower concentrations in the spring and fall (4–34 ng m ⁻³) compared to the summer and winter (37–161 ng m⁻³). PAHs in the air near Galveston Bay are derived from both combustion and petroleum vaporization. Gas exchange from the atmosphere to the surface water is estimated to be the major deposition process for PAHs (1211 μg m^{− 2} yr^{− 1}), relative to wet deposition (130 μg m⁻² yr^{− 1}) and dry deposition (99 μg m⁻² yr^{− 1}). Annual deposition of PAHs directly to Galveston Bay from the atmosphere is estimated as 2  t yr⁻¹.     

The composition and sources of PM2.5 organic aerosol in two urban areas of Chile

Fine particle (PM_2.5) samples were collected, using a charcoal diffusion denuder, in two urban areas of Chile, Santiago and Temuco, during the winter and spring season of 1998. Molecular markers of the organic aerosol were determined using GC/MS. Diagnostic ratios and molecular tracers were used to investigate the origin of carbonaceous aerosols. As main sources, road and non-road engine emissions in Santiago, and wood burning in Temuco were identified. Cluster analysis was used to compare the chemical characteristics of carbonaceous aerosols between the two urban environments. Distinct differences between Santiago and Temuco samples were observed. High concentrations of isoprenoid (30–69 ng m⁻³) and unresolved complex mixture (UCM) of hydrocarbons (839–1369 ng m⁻³) were found in Santiago. High concentrations of polynuclear aromatic hydrocarbons (751±304 ng m⁻³) and their oxygenated derivatives (4±2 ng m⁻³), and of n-alk-1-enes (16±13 ng m⁻³) were observed in Temuco.     

Temporal variability of mercury speciation in urban air

Semi-continuous measurements of ambient mercury (Hg) species were performed in Detroit, MI, USA for the calendar year 2003. The mean (±standard deviation) concentrations for gaseous elemental mercury (GEM), particulate mercury (HgP), and reactive gaseous mercury (RGM) were 2.2±1.3 ng m⁻³, 20.8±30.0, and 17.7±28.9 pg m⁻³, respectively. A clear seasonality in Hg speciation was observed with GEM and RGM concentrations significantly (p<0.001) greater in warm seasons, while HgP concentrations were greater in cold seasons. The three measured Hg species also exhibited clear diurnal trends which were particularly evident during the summer months. Higher RGM concentrations were observed during the day than at night. Hourly HgP and GEM concentrations exhibited a similar diurnal pattern with both being inversely correlated with RGM. Multivariate analysis coupled with conditional probability function analysis revealed the conditions associated with high Hg concentration episodes, and identified the inter-correlations between speciated Hg concentrations, three common urban air pollutants (sulfur dioxide, ozone, and nitric oxides), and meteorological parameters. This analysis suggests that both local and regional sources were major factors contributing to the observed temporal variations in Hg speciation. Boundary layer dynamics and the seasonal meteorological conditions, including temperature and moisture content, were also important factors affecting Hg variability.     

Nitric oxide emissions from soils amended with municipal waste biosolids

Land spreading nitrogen-rich municipal waste biosolids (NO₃⁻-N<256 mg N kg⁻¹ dry weight, NH₃-N∼23,080 mg N kg⁻¹ dry weight, Total Kjeldahl N∼41,700 mg N kg⁻¹ dry weight) to human food and non-food chain land is a practice followed throughout the US. This practice may lead to the recovery and utilization of the nitrogen by vegetation, but it may also lead to emissions of biogenic nitric oxide (NO), which may enhance ozone pollution in the lower levels of the troposphere. Recent global estimates of biogenic NO emissions from soils are cited in the literature, which are based on field measurements of NO emissions from various agricultural and non-agricultural fields. However, biogenic emissions of NO from soils amended with biosolids are lacking. Utilizing a state-of-the-art mobile laboratory and a dynamic flow-through chamber system, in-situ concentrations of nitric oxide (NO) were measured during the spring/summer of 1999 and winter/spring of 2000 from an agricultural soil which is routinely amended with municipal waste biosolids. The average NO flux for the late spring/summer time period (10 June 1999–5 August 1999) was 69.4±34.9 ng N m⁻² s⁻¹. Biosolids were applied during September 1999 and the field site was sampled again during winter/spring 2000 (28 February 2000–9 March 2000), during which the average flux was 3.6±1.7 ng N m⁻² s⁻¹. The same field site was sampled again in late spring (2–9 June 2000) and the average flux was 64.8±41.0 ng N m⁻² s⁻¹. An observationally based model, developed as part of this study, found that summer accounted for 60% of the yearly emission while fall, winter and spring accounted for 20%, 4% and 16% respectively. Field experiments were conducted which indicated that the application of biosolids increases the emissions of NO and that techniques to estimate biogenic NO emissions would, on a yearly average, underestimate the NO flux from this field by a factor of 26. Soil temperature and % water filled pore space (%WFPS) were observed to be significant variables for predicting NO emissions, however %WFPS was found to be most significant during high soil temperature conditions. In the range of pH values found at this site (5.8±0.3), pH was not observed to be a significant parameter in predicting NO emissions.     

Atmospheric mercury species in the European Arctic: Measurements and modelling

Concentrations of different species of mercury in arctic air and precipitation have been measured at Ny-Ålesund (Svalbard) and Pallas (Finland) during 1996–1997. Typical concentrations for vapour phase mercury measured at the two stations were in the range of 0.7–2 ng m⁻³ whereas particulate mercury concentrations were below 5 pg m⁻³. Total mercury in precipitation was in the range 3–30 ng l⁻¹. In order to evaluate the transport and deposition of mercury to the arctic from European anthropogenic sources, the Eulerian transport model HMET has been modified and extended to also include mercury species. A scheme for chemical conversion of elemental mercury to other species of mercury and deposition characteristics of different mercury species have been included in the model. European emission inventories for three different forms of Hg (Hg⁰, HgCl₂ and Hg_p) have been implemented in the numerical grid system for the HMET model.     

Analysis of particulate polycyclic aromatic hydrocarbons by on-line coupled supercritical fluid extraction–liquid chromatography–gas chromatography–mass spectrometry

An on-line supercritical fluid extraction–liquid chromatography–gas chromatography–mass spectrometry (SFE–LC–GC–MS) method was developed for the analysis of the particulate polycyclic aromatic hydrocarbons (PAHs). The limits of detection of the system for the quantification standards were in the range of 0.25–0.57 ng, while the limits of determinations for filter samples varied from 0.02 to 0.04 ng m⁻³ (24 h sampling). The linearity was excellent from 5 to 300 ng (R²>0.967). The analysis could be carried out in a closed system without tedious manual sample pretreatment and with no risk of errors by contamination or loss of the analytes. The results of the SFE–LC–GC–MS method were comparable with those for Soxhlet and shake-flask extractions with GC–MS. The new method was applied to the analysis of PAHs collected by high-volume filter in the Helsinki area to study the seasonal trend of the concentrations. The individual PAH concentrations varied from 0.015 to more than 1 ng m⁻³, while total PAH concentrations varied from 0.81 to 5.68 ng m⁻³. The concentrations were generally higher in winter than in summer. The mass percentage of the total PAHs in total suspended particulates ranged from 2.85×10⁻³% in July to 15.0×10⁻³% in December. Increased emissions in winter, meteorological conditions, and more serious artefacts during the sampling in summer season may explain the concentration profiles.     

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.     

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.