Oxidation of gaseous elemental mercury to gaseous divalent mercury during 2003 polar sunrise at Ny-Alesund

The springtime phenomenon, termed as the mercury depletion event (MDE), during which elemental gaseous mercury (Hg0) may be converted to a reactive form that accumulates in polar ecosystems, first noted in the Arctic, has now been observed at both poles and results in an important removal pathway for atmospheric mercury. An intensive international springtime mercury experiment was performed at Ny-Alesund, Spitsbergen, from 19 April to 13 May 2003 to study the atmospheric mercury chemistry in the Arctic environment and, in particular, the MDEs which occurred in the arctic boundary layer after polar sunrise. Automated ambient measurements of Hg0, divalent reactive gaseous mercury (RGM) and fine particulate mercury (<2.5 microm) (Hg(p)) were made at the Zeppelin Mountain Station (ZMS). During the experiment mercury concentrations in the lower atmosphere varied in synchrony with ozone levels throughout the Spring. Hg0 concentrations ranged from background levels (approximately 1.6 ng m(-3)) to undetectable values (<0.1 ng m(-3)) during the first and major MDE, while RGM data showed an opposite trend during the sampling period with concentrations increasing dramatically to a peak of 230 pg m(-3), synchronous with the depletion of Hg0. The results of a meteorological transport analysis indicate the MDEs observed at ZMS were primarily due to air masses being transported in from open water areas in the Arctic Ocean that were already depleted of Hg0 when they arrived and not due to in-situ oxidation mechanisms.     

Sources of speciated atmospheric mercury at a residential neighborhood impacted by industrial sources

Speciated measurements of atmospheric mercury plumes were obtained at an industrially impacted residential area of East St. Louis, IL. These plumes were found to result in extremely high mercury concentrations at ground level that were composed of a wide distribution of mercury species. Ground level concentrations as high as 235 ng m(-3) for elemental mercury (Hg0) and 38 300 pg m(-3) for reactive mercury species (reactive gaseous (RGM) plus particulate (PHg) mercury) were measured. The highest mercury concentrations observed during the study were associated with plumes that contained high concentrations of all mercury species (Hg0, RGM, and PHg) and originated from a source located southwest of the sampling site. Variations in proportions of Hg0/RGM/PHg among plumes, with Hg0 dominating some plumes and RGM and/or PHg dominating others, were attributed to differences in emissions from different sources. Correlations between mercury plumes and elevated NO(x) were not observed; however, a correlation between elevated SO2 and mercury plumes was observed during some but not all plume events. Despite the presence of six coal-fired power plants within 60 km of the study site, wind direction data along with Hg/SO2 and Hg/NO(x) ratios suggest that high-concentration mercury plumes impacting the St. Louis-Midwest Particle Matter Supersite are attributable to local point sources within 5 km of the site.     

Atmospheric mercury (Hg) in the Adirondacks: concentrations and sources

Hourly averaged gaseous elemental Hg (GEM) concentrations and hourly integrated reactive gaseous Hg (RGM), and particulate Hg (Hg(p)) concentrations in the ambient air were measured at Huntington Forest in the Adirondacks, New York from June 2006 to May 2007. The average concentrations of GEM, RGM, and Hg(p) were 1.4 +/- 0.4 ng m(-3), 1.8 +/- 2.2 pg m(-3), and 3.2 +/- 3.7 pg m(-3), respectively. RGM represents < 3.5% of total atmospheric Hg or total gaseous Hg (TGM: GEM + RGM) and Hg(p) represents < 3.0% of the total atmospheric Hg. The highest mean concentrations of GEM, RGM, and Hg(p) were measured during winter and summer whereas the lowest mean concentrations were measured during spring and fall. Significant diurnal patterns were apparent in warm seasons for all species whereas diurnal patterns were weak in cold seasons. RGM was better correlated with ozone concentration and temperature in both warm (rho (RGM - ozone) = 0.57, p < 0.001; rho (RGM - temperature) = 0.62, p < 0.001) and cold seasons (rho (RGM - ozone) = 0.48, p = 0.002; rho (RGM - temperature) = 0.54, p = 0.011) than the other species. Potential source contribution function (PSCF) analysis was applied to identify possible Hg sources. This method identified areas in Pennsylvania, West Virginia, Ohio, Kentucky, Texas, Indiana, and Missouri, which coincided well with sources reported in a 2002 U.S. mercury emissions inventory.     

Measurements of mercury in dew: atmospheric removal of mercury species to a wetted surface

The importance of dew in the mercury cycle was investigated during three sampling periods in the Great Lakes region and one in the Florida Everglades. Mercury concentrations ranged from 1.0 to 22.6 ng/L in dew. Deposition per dew event was, on average, lowest at a remote site on Lake Superior (0.31 ng/m2) and highest in the Florida Everglades (1.4 ng/m2). The estimated mercury deposition to the canopy associated with dew approximately equaled that of precipitation during the wintertime Everglades study. Relative to other trace elements (Mg, Ti, V, Mn, Ni, Cu, As, Sr, Cd, Sb, La, Ce, Pb), mercury was found to be more enriched in rain than dew, suggesting the importance of gas scavenging for precipitation. The fraction of mercury in dew from particulate deposition was estimated to average 40%, with the remaining contribution from reactive gaseous Hg (RGM). RGM, for which little reliable data exists, was measured in the Everglades and was significantly reduced at the start of a dew event, indicating pronounced removal of this soluble mercury species to wetted surfaces. The first estimates of RGM deposition velocities based on mercury flux measurements are reported here and range up to 1.6 cm/s.     

Concentration and dry deposition of mercury species in arid south central New Mexico (2001-2002)

This research was initiated to characterize atmospheric deposition of reactive gaseous mercury (RGM), particulate mercury (HgP; <2.5 microm), and gaseous elemental mercury (Hg0) in the arid lands of south central New Mexico. Two methods were field-tested to estimate dry deposition of three mercury species. A manual speciation sampling train consisting of a KCl-coated denuder, 2.5 microm quartz fiber filters, and gold-coated quartz traps and an ion-exchange membrane (as a passive surrogate surface) were deployed concurrently over 24-h intervals for an entire year. The mean 24-h atmospheric concentration for RGM was 6.8 pg m(-3) with an estimated deposition of 0.10 ng m(-2) h(-1). The estimated deposition of mercury to the passive surrogate surface was much greater (4.0 ng m(-2) h(-1)) but demonstrated a diurnal pattern with elevated deposition from late afternoon to late evening (1400-2200; 8.0 ng m(-2) h(-1)) and lowest deposition during the night just prior to sunrise (2200-0600; 1.7 ng m(-2) h(-1)). The mean 24-h atmospheric concentrations for HgP and Hg0 were 1.52 pg m(-3) and 1.59 ng m(-3), respectively. Diurnal patterns were observed for RGM with atmospheric levels lowest during the night prior to sunrise (3.8 pg m(-3)) and greater during the afternoon and early evening (8.9 pg m(-3)). Discernible diurnal patterns were not observed for either HgP or Hg0. The total dry deposition of Hg was 5.9 microg m-2 year-' with the contribution from the three species as follows: RGM (0.88 microg m(-2) year(-1)), HgP (0.025 microg m(-2) year(-1)), and Hg0 (5.0 microg m(-2) year(-1)). The annual wet deposition for total mercury throughout the same collection duration was 4.2 microg m(-2) year (-1), resulting in an estimated total deposition of 10.1 microg m(-2) year(-1) for Hg. On one sampling date, enhanced HgP (12 pg m(-3)) was observed due to emissions from a wildfire approximately 250 km to the east.     

Automated speciated mercury measurements in Michigan

Automated speciated mercury measurements were made at a rural (Dexter, MI) and an urban (Detroit, MI) site in Michigan during selected times from 1999 to 2002 to assess the concentrations of elemental (Hg0), reactive gaseous (RGM), and particulate mercury (Hgp) in these environments. Here we present the first-ever reported values for RGM in Michigan. Median RGM concentrations were 2.21-2.93 pg m(-3) at Dexter and were 3-11 times higher in Detroit at 6.41-22.0 pg m(-3). Maximum RGM concentrations of 38.7 pg m(-3) and 270 pg m(-3) were observed in Dexter and Detroit, respectively. Measured RGM/Hg0 ratios were in the range of 0.04-11.60% indicating that at times RGM comprises greater than the currently held view of 5% of total gaseous mercury in the air. Well-pronounced diurnal patterns of RGM were observed at the rural site, whereas the urban site exhibited patterns that were influenced by nighttime emissions and regional transport. An analysis of RGM/Hgp ratios at the urban site when combined with trajectory analysis suggests that the site receives mercury inputs from both local and regional sources. Episodes of elevated ozone concentrations which were accompanied by increases in RGM concentrations were observed to occur in the late afternoon and overnight. These may be evidence of advection of ozone and RGM over long distances to the site.     

Development and characterization of an annular denuder methodology for the measurement of divalent inorganic reactive gaseous mercury in ambient air

Atmospheric mercury is predominantly present in the gaseous elemental form (Hg0). However, anthropogenic emissions (e.g., incineration, fossil fuel combustion) emit and natural processes create particulate-phase mercury(Hg(p)) and divalent reactive gas-phase mercury (RGM). RGM species (e.g., HgCl2, HgBr2) are water-soluble and have much shorter residence times in the atmosphere than Hg0 due to their higher removal rates through wet and dry deposition mechanisms. Manual and automated annular denuder methodologies, to provide high-resolution (1-2 h) ambient RGM measurements, were developed and evaluated. Following collection of RGM onto KCl-coated quartz annular denuders, RGM was thermally decomposed and quantified as Hg0. Laboratory and field evaluations of the denuders found the RGM collection efficiency to be >94% and mean collocated precision to be <15%. Method detection limits for sampling durations ranging from 1 to 12 h were 6.2-0.5 pg m(-3), respectively. As part of this research, the authors observed that methods to measure Hg(p) had a significant positive artifact when RGM coexists with Hg(p). This artifact was eliminated if a KCl-coated annular denuder preceded the filter. This new atmospheric mercury speciation methodology has dramatically enhanced our ability to investigate the mechanisms of transformation and deposition of mercury in the atmosphere.     

Assessing the potential for re-emission of mercury deposited in precipitation from arid soils using a stable isotope

A solution containing 198Hg in the form of HgCl2 was added to a 4 m2 area of desert soils in Nevada, and soil Hg fluxes were measured using three dynamic flux chambers. There was an immediate release of 198Hg after it was applied, and then emissions decreased exponentially. Within the first 6 h after the isotope was added to the soil, approximately 12 ng m(-2) of 198Hg was emitted to the atmosphere, followed by a relatively steady flux of the isotope at 0.2 +/- 0.2 ng m(-2) h(-1) for the remainder of the experiment (62 days). Over this time, approximately 200 ng m(-2) or 2% of the 198Hg isotope was emitted from the soil, and we estimate that approximately 6% of the isotope would be re-emitted in a year's time. During the experiment, dry deposition of elemental Hg from the atmosphere was measured with an average deposition rate of 0.2 +/- 0.1 ng m(-2) h(-1). Emission of ambient Hg from the soil was observed after soil wetting with the isotope solution and after a storm event. However, the added moisture from the storm event did not affect 198Hg flux. Results suggest that in this desert environment, where there is limited precipitation, Hg deposited by wet processes is not readily re-emitted and that dry deposition of elemental Hg may be an important process.     

Global source-receptor relationships for mercury deposition under present-day and 2050 emissions scenarios

Global policies regulating anthropogenic mercury require an understanding of the relationship between emitted and deposited mercury on intercontinental scales. Here, we examine source-receptor relationships for present-day conditions and four 2050 IPCC scenarios encompassing a range of economic development and environmental regulation projections. We use the GEOS-Chem global model to track mercury from its point of emission through rapid cycling in surface ocean and land reservoirs to its accumulation in longer lived ocean and soil pools. Deposited mercury has a local component (emitted Hg(II), lifetime of 3.7 days against deposition) and a global component (emitted Hg(0), lifetime of 6 months against deposition). Fast recycling of deposited mercury through photoreduction of Hg(II) and re-emission of Hg(0) from surface reservoirs (ice, land, surface ocean) increases the effective lifetime of anthropogenic mercury to 9 months against loss to legacy reservoirs (soil pools and the subsurface ocean). This lifetime is still sufficiently short that source-receptor relationships have a strong hemispheric signature. Asian emissions are the largest source of anthropogenic deposition to all ocean basins, though there is also regional source influence from upwind continents. Current anthropogenic emissions account for only about one-third of mercury deposition to the global ocean with the remainder from natural and legacy sources. However, controls on anthropogenic emissions would have the added benefit of reducing the legacy mercury re-emitted to the atmosphere. Better understanding is needed of the time scales for transfer of mercury from active pools to stable geochemical reservoirs.     

Estimation of mercury vapor flux from natural substrate in Nevada

The contribution of mercury to the atmosphere from natural sources is not well-quantified, particularly at the regional scale. This modeling study employed a Geographic Information Systems (GIS) approach to estimate mercury flux from substrate in Nevada, which lies within one of the global belts of geologic Hg enrichment. In situ mercury flux measurements were taken from a variety of substrate types with a wide range of mercury concentrations. This empirical data forms the basis of equations applied to a database of over 71,000 rock and soil samples used in scaling mercury flux for Nevada. The GIS was employed to spatially model estimated flux values according to sample type, geology, presence/absence of hydrothermal alteration, and meteorological conditions. The area average flux calculated for Nevada adjusted for meteorological conditions is 4.2 +/- 1.4 ng m-2 h-1, which corresponds to a approximately 29 kg daily emission of mercury. Areas of hydrothermal alteration emit 12.9 +/- 3.6 ng m-2 h-1, accounts for 22% of net mercury emissions yet represents only 7% of the area of Nevada. Unaltered geologic units have low fluxes (3.5 +/- 1.2 ng m-2 h-1) but, because of their large area, emit 78% of the total mercury.     

Methylated mercury species in Canadian high Arctic marine surface waters and snowpacks

We sampled seawater and snowpacks in the Canadian high Arctic for methylated species of mercury (Hg). We discovered that, although seawater sampled under the sea ice had very low concentrations of total Hg (THg, all forms of Hg in a sample; on average 0.14-0.24 ng L(-1)), 30-45% of the THg was in the monomethyl Hg (MMHg) form (on average 0.057-0.095 ng L(-1)), making seawater itself a direct source of MMHg for biomagnification through marine food webs. Seawater under the ice also contained high concentrations of gaseous elemental Hg (GEM; 129 +/- 36 pg L(-1)), suggesting that open water regions such as polynyas and ice leads were a net source of approximately 130 +/- 30 ng Hg m(-2) day(-1) to the atmosphere. We also found 11.1 +/- 4.1 pg L(-1) of dimethyl Hg (DMHg) in seawater and calculated that there could be a significant flux of DMHg to the atmosphere from open water regions. This flux could then resultin MMHg deposition into nearby snowpacks via oxidation of DMHg to MMHg in the atmosphere. In fact, we found high concentrations of MMHg in a few snowpacks near regions of open water. Interestingly, we discovered a significant log-log relationship between Cl- concentrations in snowpacks and concentrations of THg. We hypothesize that as Cl- concentrations in snowpacks increase, inorganic Hg(II) occurs principally as less reducible chloro complexes and, hence, remains in an oxidized state. As a result, snowpacks that receive both marine aerosol deposition of Cl- and deposition of Hg(II) via springtime atmospheric Hg depletion events, for example, may contain significant loads of Hg(II). Overall, though, the median wet/dry loads of Hg in the snowpacks we sampled in the high Arctic (5.2 mg THg ha(-1) and 0.03 mg MMHg ha(-1)) were far below wet-only annual THg loadings throughout southern Canada and most of the U.S. (22-200 mg ha(-1)). Therefore, most Arctic snowpacks contribute     

Enhanced deposition and bioaccumulation of mercury in Antarctic terrestrial ecosystems facing a coastal polynya

Mercury emitted by anthropogenic and natural sources occurs in the atmosphere mostly in the gaseous elemental form, which has a long lifetime in tropical and temperate regions. Once deposited in terrestrial and aquatic ecosystems the metal is partly re-emitted into the air, thus assuming the characteristics of global pollutants such as persistent volatile chemicals. In polar regions, during and after the sunrise, the photochemically driven oxidation of gaseous Hg by reactive halogens may result in areas of greatly enhanced Hg deposition. Mercury concentrations in soils, lichens, and mosses collected in a stretch between 74 degrees 30' S and 76 degrees 00' S, in ice-free coastal areas of Victoria Land facing the Terra Nova Bay coastal polynya, were higher than typical Antarctic baselines. The finding of enhanced Hg bioaccumulation in Antarctic terrestrial ecosystems facing a coastal polynya strongly supports recent speculations on the role of ice crystals ("frost flowers") growing in polynyas as a dominant source of sea salt aerosols and bromine compounds, which are involved in springtime mercury depletion events (MDEs). These results raise concern aboutthe possible environmental effects of changes in regional climate and sea ice coverage, and on the possible role of Antarctica as a sink in the mercury cycle.     

Processes influencing rainfall deposition of mercury in Florida

The primary goal of the Florida Atmospheric Mercury Study (FAMS) was to quantify the atmospheric deposition of Hg throughout Florida. Monthly integrated precipitation and weekly integrated particulate samples were collected at 10 sites in Florida for periods ranging from 2 to 5 yr. The monthly rainfall across the state and the concentrations of Hg in wet-only and bulk deposition increased by a factor of 2-3 during the summertime "wet season" (May-October). These parallel increases in rainfall amount and Hg concentration resulted in 5-8-fold increases in rainfall Hg deposition during the wet season. The annual volume-weighted Hg concentrations ranged from 14 +/- 2 to 16 +/- 2 ng/L across southern Florida, and the annual rainfall Hg fluxes ranged from 20 +/- 3 to 23 +/- 3 micrograms m-2 yr-1. The weekly integrated particulate Hg concentrations in southern Florida were low (4.9-9.3 pg/m3) and did not exhibit strong seasonal variability. Considering the pronounced seasonal pattern in rainfall Hg deposition, the relatively uniform summertime rainfall Hg concentrations, and the low concentrations of particulate Hg, we conclude that processes other than particulate Hg transport and scavenging govern rainfall Hg deposition in southern Florida. We hypothesize that long-range transport of reactive gaseous Hg (RGM) species coupled with strong convective thunderstorm activity during the summertime represents > 50% of the Hg deposition in southern Florida. Model calculations indicate that local anthropogenic particulate Hg and RGM emissions account for 30-46% of the summertime rainfall Hg deposition across the southern Florida peninsula.     

Deposition and emission of gaseous mercury to and from Lake Michigan during the Lake Michigan Mass Balance Study (July, 1994-October, 1995)

This paper presents measurements of dissolved gaseous mercury (DGM) concentrations in Lake Michigan and the application of a mechanistic approach to estimate deposition and emission fluxes of gaseous mercury (Hg2+ and Hg0) to and from Lake Michigan. Measurements of DGM concentrations made during May and July, 1994 and January, 1995 indicate that Lake Michigan was supersaturated with DGM suggesting that transfer of Hg0 occurs from the water to the atmosphere. Over-water concentrations of gaseous Hg2+ were estimated from total gaseous Hg (TGM) concentrations measured at five sites in the basin and used to model dry deposition fluxes of Hg2+. The modeling approach combines estimates of dry deposited Hg2+ with known photochemical and biotic reduction rates to form Hg0, which is available for re-emission. The model accounts for temporal and spatial variations in the deposition velocity of gaseous Hg2+ and the transfer velocity of Hg0 using high temporal and spatial resolution meteorological data. The modeled DGM concentrations agree well with the observed DGM concentrations in Lake Michigan. The modeled dry deposition fluxes of Hg2+ (286-797 kg yr(-1)) are very similar to the emission fluxes of Hg0 (320-959 kg yr(-1)), depending on the gaseous Hg2+ concentration used in the model.     

Rapid reduction and reemission of mercury deposited into snowpacks during atmospheric mercury depletion events at churchill, Manitoba, Canada

Mercury (Hg) in some Arctic marine mammals has increased to levels that may be toxic to Northern peoples consuming them as traditional food. It has been suggested that sunlight-induced atmospheric reactions called springtime atmospheric Hg depletion events (AMDEs) result in the loading of -150-300 tons of Hg to the Canadian Arctic archipelago each spring and that AMDEs are the ultimate source of Hg to Arctic foodwebs. AMDEs result from the oxidation of gaseous elemental Hg0 (GEM) in Arctic atmospheres to reactive gaseous Hg (RGM) and particulate Hg (pHg), both of which fall out of the atmosphere to snowpacks. We studied the springtime cycling of Hg between air and snowpacks near Churchill, Manitoba, for 2 years to determine the net input of Hg to Hudson Bay from AMDEs. In 2004, we monitored atmospheric concentrations of GEM, pHg, and RGM while simultaneously measuring concentrations of total Hg (THg) in surface snow collected over the sea ice on Hudson Bay. During numerous springtime AMDEs, concentrations of THg in surface snow increased, often to over 60 ng/L, demonstrating that AMDEs resulted in deposition of oxidized Hg (Hg(II)) to snowpacks. However, immediatelyfollowing AMDEs, average concentrations of THg in snow declined drastically from between 67.8+/-7.7 ng/L during AMDEs to only 4.25+/-1.85 ng/L four or more days following them. In 2003, we measured THg in surface snow collected daily over the sea ice and total gaseous Hg (TGM) concentrations in the interstitial airspaces of snowpacks. When concentrations of THg in the surface snow decreased, concentrations of TGM in interstitial airspaces of the snowpack increased sharply from between approximately 1.4-3.4 ng/m(3) to between approximately 20-150 ng/m(3), suggesting thatthere was a reduction of deposited Hg(II) to GEM, which then diffused out of snowpacks. At snowmelt in both 2003 and 2004, average concentrations of THg in meltwater collected over Hudson Bay were only 4.04+/-2.01 ng/L. Using concentrations of THg in meltwater and snow water equivalent, we estimated a net springtime loading of only 2.1+/-1.7 mg/ha of Hg to Hudson Bay from AMDEs, indicating that only a small portion of the Hg(II) deposited during AMDEs enters Hudosn Bay each spring.     

Rapid release of mercury from intertidal sediments exposed to solar radiation: a field experiment

There is increasing evidence of the primary importance of photochemical reactions and transfer of gaseous mercury to the atmosphere. Although mercury in aquatic sediments is efficiently retained, resuspension and bioturbation in intertidal sediments may expose temporarily anoxic sediments to solar radiation. Field experiments were performed to investigate these processes. Anoxic sediments from two areas in the Tagus estuary with different degrees of Hg contamination (experiments I and II) were homogenized and distributed into two sets of 36 uncovered Petri dishes. The samples were placed on the intertidal sediments and exposed to direct solar radiation and kept under dark (control) for 6-8 h. The decrease rates of acid volatile sulfides (abrupt in the first 3 h) and of pyrite (linear) were the same in sediments under solar radiation and dark. The total Hg concentrations were relatively constant in sediments kept in dark, but decreased from 17.6 to 7.65 and 3.45 to 1.35 nmol g(-1) in experiments I and II, respectively. In those exposed to solar radiation during the period of higher UV intensity. Similar evolutions were found in nonreactive Hg in pore waters (3.00-2.59 and 0.725-0.105 nM). On the contrary, reactive Hg was higher in pore waters of the sediments exposed to solar radiation and increased with time, from 424 to 845 pM and 53 to 193 pM. These results indicate that most mercury released in pore waters was photochemically reduced in a short period of time and escaped rapidly to the atmosphere. Episodes of bottom resuspension and bioturbation in the intertidal sediments enhance the transfer of gaseous mercury to the atmosphere.     

Mercury emissions from cement-stabilized dredged material

Upland placement of dredged materials from navigation channels in the New York/New Jersey Harbor is currently being used to manage sediments deemed inappropriate for open water disposal. Although upland placement sites are equipped with engineering controls (leachate collection and/or barrier walls), little is known of the potential impacts of this approach to air quality. The aim of this study was to estimate the flux of mercury to the atmosphere from New York/New Jersey Harbor stabilized dredged material (SDM) that was used for land reclamation at a site in northeastern New Jersey. Total gaseous mercury (TGM) was measured at a site receiving SDM in August and October 2001 and May and November 2002. TGM was also monitored at an urban reference site 3.5 km west of the SDM site in September 2001 and from February 2002 to July 2002 and from October 2002 to February 2003. The concentration of TGM at the urban reference site averaged 2.2 +/- 1.1 ng m(-3), indicating some local contribution to the Northern Hemisphere background. TGM concentrations exhibited seasonality with the highest values in summer (3.3 +/- 2.1 ng m(-3) in June 2002) and the lowest in winter (1.7 +/- 0.6 ng m(-3) in January 2003). TGM concentrations at the SDM placement site ranged from 2 to 7 ng m(-3) and were significantly higher (p < 0.001) than those at the urban reference site. Sediment-air fluxes of Hg at the SDM placement site estimated by the micrometeorological technique ranged from -13 to 1040 ng m(-2) h(-1) (sediment to air fluxes being positive) and were significantly correlated to solar radiation (r2 = 0.81). The estimated contribution of Hg emissions from land-applied SDM to local TGM concentrations was found to be negligible (<4%). However, the estimated annual volatilization rate of TGM atthe SDM site (130 kg y(-1))was comparable to those of other industrial sources in New Jersey (140-450 kg y(-1)).     

Novel mercury control technology for solid waste incineration: sodium tetrasulfide (STS) as mercury capturing agent

Traditional pollution control technologies are able to capture oxidized forms of mercury to some extent; however, they show low efficiency for the control of elemental mercury emissions. This study developed a novel mercury removal technology: injection of sodium tetrasulfide (Na2S4) dissolved in the sodium hydroxide (NaOH) solution in the spray-dryer system. The effects of flue gas temperature and Na2S4 level in flue gas on the mercury removal efficiency were investigated. Na2S4 was decomposed into Na2S (S2-) and elemental S (S0), which reacted with HgCl2 and elemental Hg (Hg0), and HgS was then formed. Under the optimized operation parameters, this technology can simultaneously remove over 88% of HgCl2 and more than 90% of Hg0 from a flue gas stream containing about 400 microg m(-3) Hg0 and 1200 microg m(-3) HgCl2. The increased flue gas temperature (>170 degrees C) and the decreased Na2S4-to-Hg mass ratio (S-Hg-R) (<2.0) had negative effects on the reactions of gaseous mercury (HgCl2 + Hg0) with ionic sulfur (S2-) and S0. All the experiments were conducted in a full scale hospital-waste incinerator with a capability of 20 tons per day (TPD).     

Continuous analysis of dissolved gaseous mercury and mercury volatilization in the upper St. Lawrence River: exploring temporal relationships and UV attenuation

The formation and volatilization of dissolved gaseous mercury (DGM) is an important mechanism by which freshwaters may naturally reduce their mercury burden. Continuous analysis of surface water for diurnal trends in DGM concentration (ranging from 0 to 60.4 pg L(-1); n=613), mercury volatilization (ranging from 0.2 to 1.1 ng m(-2) h(-1); n=584), and a suite of physical and chemical measurements were performed during a 68 h period in the St. Lawrence River near Cornwall (Ontario, Canada) to examine the temporal relationships governing mercury volatilization. No lag-time was observed between net radiation and OGM concentrations (highest cross-correlation of 0.817), thus supporting previous research indicating faster photoreduction kinetics in rivers as compared to lakes. A significant lag-time (55-145 min; maximum correlation = 0.625) was observed between DGM formation and mercury volatilization, which is similar to surface water Eddy diffusion times of 42-132 min previously measured in the St. Lawrence River. A depth-integrated DGM model was developed using the diffuse integrated vertical attenuation coefficients for UVA and UVB (K(dI UVA) = 1.45 m(-1) K(dI UVB)= 3.20 m(-1)) Low attenuation of solar radiation was attributed to low concentrations of dissolved organic carbon (mean = 2.58 mg L(-1) and particulate organic carbon (mean = 0.58 mg L(-1) in the St. Lawrence River. The depth-integrated DGM model developed found that the top 0.3 m of the water column accounted for only 26% of the total depth-integrated DGM. A comparison with volatilization data indicated that a large portion (76% or 10.5 ng m(-2) of the maximum depth-integrated DGM (13.8 ng m(-2))is volatilized over a 24 h period. Therefore, at least 50% of all DGM volatilized was produced at depths below 0.3 m. These results highlight the importance of solar attenuation in regulating DGM formation with depth. The results also demonstrate both the fast formation of DGM in rivers and the importance of understanding DGM dynamics with depth as opposed to surface waters.     

Laboratory investigation of the potential for re-emission of atmospherically derived Hg from soils

This paper presents data from controlled laboratory experiments focused on investigating the effect of moisture and visible and ultraviolet light on the emission and re-emission of mercury (Hg) from two soils, one with low or background Hg concentrations (14 ng g(-1)) and a soil naturally enriched in Hg (4800 ng g(-1)). Water addition was found to increase emissions from dry soils by an amount greater than that occurring during exposure to PAR or UV-A radiation, whereas UV-B and UV-C exposures facilitated the greatest release. Over all exposures, only a small percentage of Hg(ll) added in a wet spike simulating a precipitation input was released immediately after addition (< 3%). The majority of the Hg being released during all exposures was indigenous and either an original component of the soil or derived from past wet and dry deposition. Under dark and light conditions, elemental Hg was deposited to the dry low Hg-containing soil. On the basis of experimental results, it is hypothesized that dry deposition of gaseous elemental Hg is an important input to low Hg soils and that light, water, and UV-A exposure promote desorption and re-emission of elemental Hg. UV-B exposure is hypothesized to promote indirect photoreduction of Hg(II) existing in the soil. The available pool and the form of Hg in the soil, as well as the chemistry of the soil, will determine the overall flux response to environmental stimulation of emissions.