Total Gaseous Mercury Emissions Research Articles

Isotopic Characterization of Gaseous Mercury and Particulate Water-Soluble Organic Carbon Emitted from Open Grass Field Burning in Aso, Japan

Biomass burning is one of the major emitters of airborne particulate matter (PM) and gaseous mercury. In order to apply the isotopic fingerprinting method to process identification and source apportionment studies, isotopic characterizations of targeted substances at emission are indispensable. Here, we report the stable isotopic composition of total gaseous mercury (TGM) and the stable and radiocarbon isotopic composition of low-volatile water-soluble nitrogen (LV-WSN) and organic carbon (LV-WSOC) in PM emitted from open grass field burning in the Aso region of Japan. The measurement results showed that TGM concentrations in the air increased during the open field burning events, indicating the presence of TGM emissions. The results of LV-WSN analysis showed very low concentrations; therefore, the stable nitrogen isotope ratios could not be measured. The stable mercury isotope ratios exhibited lighter composition than those observed during non-biomass-burning days. The analysis of LV-WSOC revealed heavy stable carbon isotope ratios (average ± SD, −18 ± 2‰), suggesting a substantial contribution from C4 plant carbon. The 14C analysis showed that more than 98% of the LV-WSOC was modern carbon, indicating the contribution of plant carbon to PM emitted from biomass burning. The findings here provide reference isotope compositions of TGM and particulate LV-WSOC from biomass burning in this region.

Soil–atmosphere exchange flux of total gaseous mercury (TGM) at subtropical and temperate forest catchments

Abstract. Evasion from soil is the largest source of mercury (Hg) to the atmosphere from terrestrial ecosystems. To improve our understanding of controls and in estimates of forest soil–atmosphere fluxes of total gaseous Hg (TGM), measurements were made using dynamic flux chambers (DFCs) over 130 and 96 d for each of five plots at a subtropical forest and a temperate forest, respectively. At the subtropical forest, the highest net soil Hg emissions were observed for an open field (24 ± 33 ng m−2 h−1), followed by two coniferous forest plots (2.8 ± 3.9 and 3.5 ± 4.2 ng m−2 h−1), a broad-leaved forest plot (0.18 ± 4.3 ng m−2 h−1) and the remaining wetland site showing net deposition (−0.80 ± 5.1 ng m−2 h−1). At the temperate forest, the highest fluxes and net soil Hg emissions were observed for a wetland (3.81 ± 0.52 ng m−2 h−1) and an open field (1.82 ± 0.79 ng m−2 h−1), with lesser emission rates in the deciduous broad-leaved forest (0.68 ± 1.01 ng m−2 h−1) and deciduous needle-leaved forest (0.32 ± 0.96 ng m−2 h−1) plots, and net deposition at an evergreen pine forest (−0.04 ± 0.81 ng m−2 h−1). High solar radiation and temperature during summer resulted in the high Hg emissions in the subtropical forest and the open field and evergreen pine forest at the temperate forest. At the temperate deciduous plots, the highest Hg emission occurred in spring during the leaf-off period due to direct solar radiation exposure to soils. Fluxes showed strong positive relationships with solar radiation and soil temperature and negative correlations with ambient air TGM concentration in both the subtropical and temperate forests, with area-weighted compensation points of 6.82 and 3.42 ng m−3, respectively. The values of the compensation points suggest that the atmospheric TGM concentration can play a critical role in limiting TGM emissions from the forest floor. Climate change and land use disturbance may increase the compensation points in both temperate and subtropical forests. Future research should focus on the role of legacy soil Hg in reemissions to the atmosphere as decreases in primary emissions drive decreases in TGM concentrations and disturbances of climate change and land use.

Observation and estimation of mercury exchange fluxes from soil under different crop cultivars and planting densities in North China Plain

The emission of mercury (Hg) from cropland soil greatly affects the global Hg cycle. Combinations of different crop cultivars and planting densities will result in different light transmittance under canopies, which directly affects the solar and heat radiation flux received by the soil surface below crops. In turn, this might lead to differences in the soil–air total gaseous mercury (TGM) exchange under different cropping patterns. However, soil–air TGM exchange fluxes in croplands under differing canopies have been poorly investigated. Here, a one-year observation of TGM exchange flux was conducted for cropland soils covering five different crop cultivars and three planting densities in North China Plain using the dynamic flux chamber method. The results showed that light transmittance under the canopies was the key control on soil–air TGM exchange fluxes. High light transmittance can enhance soil TGM emission rates and increase the magnitude of diurnal variations in soil–air TGM exchange fluxes. Furthermore, we found that there were piecewise–function relationships (Peak function–constant equation) between light transmittance under the different canopies and the numbers of days after crop sowing. The soil–air TGM exchange fluxes showed a parabolic response to changes in light transmittance under the different canopies. A second-order model was established for the response relationship between soil–air TGM exchange flux and soil Hg concentration, total solar radiation above the canopy, and numbers of days after sowing. The estimated annual average soil–air TGM exchange flux was 5.46 ± 21.69 ng m−2 h−1 at corn–wheat rotation cropland with 30 cm row spacing using this second-order model. Our results might a data reference and a promising foundation for future model development of soil–air TGM exchange in croplands under different crop cultivars and planting densities.

The soil displacement measurement of mercury emission flux of the sewage irrigation farmlands in Northern China

ABSTRACT Mercury fate of sewage irrigation in farmlands deserves attention with increasing scarcity of freshwater resources for agriculture in the worldwide. Soil-air total gaseous mercury (TGM) fluxes from four-sewage and one-fresh water irrigated farmlands were determined simultaneously. During maize-wheat rotation, soil-air TGM fluxes showed patterns of both emission and deposition during different growth stages. It enhanced one-order of magnitude emission with increased Hg contamination from historical sewage irrigation. A linear response relationship of TGM fluxes with soil Hg concentration was found, which showed greater TGM emission potential comparing with those from forest and urban soils. However, the ratio of soil-air TGM flux in daytime to nighttime were 3.94 in maize-season and 3.41 in wheat-season, respectively, which were little related to the change in soil Hg concentration. Furthermore, soil temperature and moisture, ambient-air TGM concentration all effected TGM evasion from sewage-irrigated soils. The data presented here suggest that evasion of TGM from historical sewage irrigation farmlands with high Hg concentrations may be potential hotspots for Hg emission in atmosphere, and it was likely to underestimate Hg emissions from farmlands in existing emissions inventory. Additional regional-investigations and process-level researches are needed to better understand role of sewage irrigation farmlands in local-global Hg-biogeochemical-cycles.

Sources and Dynamic Processes Controlling Background and Peak Concentrations of TGM in Nanjing, China

Total gaseous mercury (TGM) data from urban Nanjing, at the western edge of the Yangtze River Delta (YRD) region in China, over nine months, were analyzed for peak and background mercury concentrations. The background concentration of TGM was found to be 2.2 ng∙m−3. In examining episodic influences of free tropospheric air masses on the surface TGM concentrations in Nanjing, we hypothesize heterogeneity in the global distribution of TGM concentrations in the free troposphere. The nine-month averaged diurnal cycles of TGM indicate a strong co-emission with SO2 and an underestimation of greater than 80% TGM emissions in current inventories. Regular peak concentrations of mercury were investigated and the major causes were YRD emissions, transport from rural areas, and monsoonal transport. Transport of rural emissions is hypothesized to be from illegal artisanal small-scale gold mining that are currently missing in the emission inventories. Enhancement of TGM associated with summer monsoon contributed to a maximum TGM concentration in mid-May–early June, an inverse seasonality in comparison to most other observations in China, North America, and Europe.

Mercury emissions from flooded soils and sediments in Germany are an underestimated problem: challenges for reliable risk assessments and management strategies

Environmental pollution by mercury is a world-wide problem. Particularly floodplain ecosystems are frequently affected. One example is the Elbe River in Germany and its catchment areas; large amounts of Hg from a range of anthropogenic and geogenic sources have been accumulated in the soils of these floodplains. They serve as sink for Hg originating from the surface water of adjacent river. Today, the vastly elevated Hg contents of the floodplain soils at the Elbe River often exceed even the action values of the German Soil Conservation Law. This is especially important as Hg polluted areas at the Elbe River achieve several hundred square kilometres. Thus, authorities are coerced by law to conduct an appropriate risk assessment and to implement practical actions to eliminate or reduce environmental problems. A reliable risk assessment particularly with view to organisms (vegetation as green fodder and hay production, grazing and wild animals) to avoid the transfer of Hg into the human food chain, requires an authentic determination of Hg fluxes and their dynamics since gaseous emissions from soil to atmosphere are an important pathway of Hg. However, reliable estimates of Hg fluxes from the highly polluted floodplain soils at the Elbe River and its tributaries, and its influencing factors are scarce. For this purpose, we have developed a new method to determine mercury emissions from soils at various sites. Our objectives were i) to quantify seasonal variations of total gaseous mercury (TGM) fluxes for floodplain soils at the Elbe River, ii) to provide insights into physico-chemical processes regulating these TGM fluxes, and iii) to quantify the impacts of the controlling factors soil temperature and soil water content on Hg volatilization from a typical contaminated floodplain soil within soil microcosm experiments under various controlled temperature and moisture conditions. Our study provides insight into TGM emissions from highly Hg-polluted floodplain soils in Germany and that those emissions are an underestimated problem. Current needs for reliable risk assessments, the induced implications for authorities, and future challenges will be discussed. The presented data will contribute to a better understanding of seasonal dynamics of Hg fluxes and its controlling factors. This presentation should be of large interest for a wide international audience, such as environmental scientists and managers, applied ecologists, and authorities.

Atmospheric Mercury Fluxes in a Southern Boreal Forest and Wetland

Total gaseous mercury (TGM) fluxes from the forest floor and a boreal wetland were measured by a flux chamber technique coupled with an automatic mercury vapour analyser. The fluxes were measured at three sampling sites in southern Finland, 61°14′ N, 25°04′ E in summer 2007, with additionally in situ TGM concentrations in the air at one of the sites and mercury bulk deposition at another. Most of the flux data were collected during the daytime. At one of the sites, diurnal flux behaviour was studied, and a clear cycle with an afternoon maximum and a night minimum was observed. The highest emissions (up to 3.5 ng m−2 h−1) were observed at the forest floor site having a moss and grass cover. At the wetland and litter-rich forest floor sites, the emissions were below 1 ng m−2 h−1 and sometimes negative (down to −1.0 ng m−2 h−1), indicating mercury uptake. The measured average fluxes in August were 0.9 ± 1.1 and 0.2 ± 0.3 ng m−2 h−1 for the forest floor sites and wetland sites, respectively. The flux data were compared with the mercury bulk deposition, which proved to be of the same magnitude, but opposite in sign. At the mossy forest floor site, the extrapolated TGM emissions were 130% of the Hg deposition in August 2007. Comparison with other studies showed that the fluxes in background areas are relatively uniform, regardless of measurement site location and method used. Airborne TGM remained at the background level during the study, with an average value of 1.3 ± 0.2 ng m−3; it frequently showed a diurnal cycle pattern.

Potential impact of rainfall on the air-surface exchange of total gaseous mercury from two common urban ground surfaces

Abstract The impact of rainfall on total gaseous mercury (TGM) flux from pavement and street dirt surfaces was investigated in an effort to determine the influence of wet weather events on mercury transport in urban watersheds. Street dirt and pavement are common urban ground surfaces that concentrate many substances (eroded soil, leaf and vegetation litter, automobile debris, industrial atmospheric fallout) which can contain elevated mercury concentrations. In this study, the primary analyses included (i) observing the time series flux of TGM from pavement and street dirt following surface wetting and (ii) determining if wet deposition provides a fresh source of mercury that is available for release (emission) when applied to these surfaces. Application of de-ionized water (DI) and rainwater both induced an immediate 65% increase in TGM emission from pavement (from 0.5 to 1.4 ng m−2 h−1 [based on averages]). For street dirt, an immediate 70% increase in emission was induced following DI water application (from 3.0 to 9.0 ng m−2 h−1 [based on averages]) and an immediate 30% increase in emission following rainwater application (from 4.5 to 6.5 ng m−2 h−1 [based on averages]). Both surfaces showed continuous elevated release of TGM following the initial water application stage. There was a decrease in emission as the pavement surface dried. Despite the difference in immediate TGM emission from street dirt using both solutions, statistical evaluation indicated there was no prolonged difference. This suggests that mercury in rainwater was not available for re-emission when applied to these surfaces, at least for the time frame studied (2 h after water application). Therefore, it is likely that the elevated TGM emission following water application resulted primarily from pre-existing mercury. Removal of pre-existing mercury by water application followed a zero order process for both surfaces; however, removal rates were much different for each surface (k = 0.26 ng m−2 min−1 for street dirt; k = 0.03 ng m−2 min−1 for pavement). Results from laboratory surface washing experiments revealed only 0.1% of all available surface-bound mercury on pavement was removed by surface emission 90 min after a simulated light rainfall event (0.13 cm of rainfall).

Ambient air total gaseous mercury concentrations in the vicinity of coal-fired power plants in Alberta, Canada

The Lake Wabamun area, in Alberta, is unique within Canada as there are four coal-fired power plants within a 500 km 2 area. Continuous monitoring of ambient total gaseous mercury (TGM) concentrations in the Lake Wabamun area was undertaken at two sites, Genesee and Meadows. The data were analyzed in order to characterise the effect of the coal-fired power plants on the regional TGM. Mean concentrations of 1.57 ng/m 3 for Genesee and 1.50 ng/m 3 for Meadows were comparable to other Canadian sites. Maximum concentrations of 9.50 ng/m 3 and 4.43 ng/m 3 were comparable to maxima recorded at Canadian sites influenced by anthropogenic sources. The Genesee site was directly affected by the coal-fired power plants with the occurrence of northwest winds, and this was evident by episodes of elevated TGM, NO x and SO 2 concentrations. NO x /TGM and SO 2/TGM ratios of 21.71 and 19.98 µg/ng, respectively, were characteristic of the episodic events from the northwest wind direction. AERMOD modeling predicted that coal-fired power plant TGM emissions under normal operating conditions can influence hourly ground-level concentrations by 0.46–1.19 ng/m 3 . The effect of changes in coal-fired power plant electricity production on the ambient TGM concentrations was also investigated, and was useful in describing some of the episodes.

Dynamics of mercury fluxes and their controlling factors in large Hg-polluted floodplain areas

Environmental pollution by mercury (Hg) is a considerable environmental problem world-wide. Due to the occurrence of Hg volatilization from their soils, floodplains can function as an important source of volatile Hg. Soil temperature and soil water content related to flood dynamics are considered as important factors affecting seasonal dynamics of total gaseous mercury (TGM) fluxes. We quantified seasonal variations of TGM fluxes and conducted a laboratory microcosm experiment to assess the effect of temperature and moisture on TGM fluxes in heavily polluted floodplain soils. Observed TGM emissions ranged from 10 to 850 ng m −2 h −1 and extremely exceeded the emissions of non-polluted sites. TGM emissions increased exponentially with raised air and soil temperatures in both field ( R 2: 0.49–0.70) and laboratory ( R 2: 0.99) experiments. Wet soil material showed higher TGM fluxes, whereas the role of soil water content was affected by sampling time during the microcosm experiments.

Mercury Volatilization from Three Floodplain Soils at the Central Elbe River, Germany

Wetlands at the riverside of the UNESCO Biosphere Reserve “Central Elbe” are highly contaminated by heavy metals, especially mercury (Hg). The Hg-polluted Elbe floodplain soils turn out to be a source of gaseous mercury via Hg volatilization from soil into the atmosphere. A modified field sampling method was used to measure total gaseous mercury (TGM) volatilization from three different sites at the Elbe River. The modified setup had a reduced chamber size and contained an internal gas circulation system. An in-ground stainless steel cylinder minimizes Hg volatilization from adjacent soil air. Cold vapor atomic absorption spectrometry (CV-AAS) was used to determine TGM amalgamated on gold traps. Sampled TGM amounts ranged between 0.02 and 0.63 ng (absolute), whereas the calculated Hg fluxes varied from 2.0 to 63.3 ng m−2 h−1. The modified system should allow measurements of Hg volatilization at various sites with a high spatial resolution, which should enable the study of interrelations between TGM emission and several key factors influencing Hg emission from floodplain soils at the Elbe River and other riverine ecosystems in the near future.

Optimization of a simple field method to determine mercury volatilization from soils—Examples of 13 sites in floodplain ecosystems at the Elbe River (Germany)

Mercury fluxes between soil and atmosphere have often been determined by using dynamic flux chambers and micrometeorological methods to assess ecological risks. However, both systems are complex, stationary, and expensive impeding measurements of Hg emissions at various field sites. The mobile, easy to handle, and cost-effective field method to determine total gaseous mercury (TGM), according to [Böhme, F., Rinklebe, J., Stärk, H.-J., Wennrich, R., Mothes, S., Neue, H.-U., 2005. A simple field method to determine mercury volatilisation from soils. Environ. Sci. Pollut. Res. (ESPR), 12: 133–135] creates a drop in air pressure that enhance the Hg emission. We optimized the sampling set-up using an air circulation system resulting in a continuous air flow over the soil surface. Thus, a drop in air pressure can be avoided and the detected TGM emissions are closer to reality. Additional benefits are an in-ground cylinder which inhibits lateral flow of gaseous mercury and the reduced size of the glass socket facilitating handling. To test the suitability of the optimized method, TGM emissions have been quantified on a set of Hg-contaminated riverine soils. Compared with non-polluted soils, mean Hg fluxes were strongly increased (between 138 and 711 ng m −2 h −1) and showed high spatial heterogeneity. Due to impacts of multiple environmental conditions that affect TGM emissions, no significant correlations have been found between Hg stocks in bulk soils and Hg fluxes.

Emissions of gaseous mercury from biomass burning in South America in 2005 observed during CARIBIC flights

Plumes of biomass burning effluents were observed during CARIBIC flights between São Paulo and Santiago de Chile on August 31 and October 5, 2005, as well as during the last part of the flight from Frankfurt to São Paulo on October 4, 2005. Total gaseous mercury (TGM) correlated with CO on August 31 and October 4 yielding a TGM/CO emission ratio of (1.2 ± 0.2) × 10−7 and (2.4 ± 1.0) × 10−7 mol/mol, respectively. No significant TGM/CO correlation was observed on October 5 probably because of variable background concentrations of both gases. The TGM/CO emission ratios observed here over South America fall within the rather narrow range of (0.67–2.4) × 10−7 mol/mol reported hitherto for sites geographically as different as South Africa, Canada, and the U.S.A. A total average emission of 437 Tg CO/yr from biomass burning over the years 1996–2000 implies an average TGM emission of 210–750 t/yr from biomass burning, representing 3–11% of all mercury emissions. TGM emissions from biomass burning are likely to be larger than anthropogenic emissions in the southern hemisphere during the burning season in August–October.

Total gaseous mercury emissions from mercury-enriched soil in Guizhou, China

Total gaseous mercury emissions from mercury-enriched soil in Guizhou, China

Total gaseous mercury emissions from soil in Guiyang, Guizhou, China

Guiyang is located in the Circum‐Pacific Global Mercuriferous Belt, and mercury concentrations in soil in this area are enriched. In situ total gaseous mercury (TGM) exchange fluxes between air and soil surface were intensively measured at four sampling sites in Guiyang from 21 May to 16 June 2003. Overall, net emissions were obtained from all sampling sites. Soil mercury concentration and solar radiation are proved to be the two most important parameters to control mercury emissions from soil. Meanwhile, a rain event can enhance mercury emission rate significantly. A simple model based on the linear correlation between mercury flux and solar radiation was applied to scale up mercury emissions from soil zones with different mercury concentration ranges. It is observed that mercury emission fluxes from soil in Guiyang are one order of magnitude higher than the value used in early models to represent emissions from global mercuriferous belts which is 1.1 ng m−2 h−1. The annual mercury emission from soil in Guiyang is calculated to be 408 kg, which highlights that natural emissions from soil contribute significantly to the elevated TGM concentrations in the ambient air in Guiyang.

Landfill is an important at-mospheric mercury emission source

Since municipal wastes contain refuses with high mercury contents, incineration of municipal wastes becomes the major anthropogenic atmospheric mercury emission source. In China, landfills are however the main way to dispose of municipal wastes. Total gaseous mercury (TGM) concentrations in landfill gas of Gaoyan sanitary landfill located in suburb of Guiyang City were monitored using a high temporal resolved automated mercury analyzer, and mono-methylmercury (MMHg) and dimethylmercury (DMHg) concentrations in landfill gas were also measured using GC coupled with the cold vapor atomic fluorescence (CVAFS) method. Meanwhile, the TGM exchange fluxes between exposed waste and air and the soil surface of the landfill and air, were measured using low Hg blank quartz flux chamber coupled with high temporal resolved automated mercury analyzer technique. TGM concentrations in landfill gas from half year filling area averaged out at 665.52 ±291.25 ng/m3, which is comparable with TGM concentrations from flue gas of a small coal combustion boiler in Guiyang. The average MMHg and DMHg concentrations averaged out at 2.06 ±1.82 ng/m3 and 9.50±5.18 ng/m3, respectively. It is proven that mercury emission is the predominant process at the surfaces of both exposed wastes and soil of landfill. Landfills are not only TGM emission source, but also methylmercury emission source to the ambient air. There are two ways to emit mercury to the air from landfills, one is with the landfill gas through landfill gas duct, and the other through soil/air exchange. The Hg emission processes from landfills are controlled by meteorological parameters.

Mercury emissions from the August 2001 wildfires in Washington State and an agricultural waste fire in Oregon and atmospheric mercury budget estimates

Smoke plumes from large wildfires burning in late August 2001 in the temperate forests along the eastern slopes of the Cascade Mountains in Washington State and from a wheat stubble fire on the northeastern plain of Oregon were sampled for mercury from the University of Washington's Convair 580 research aircraft. Total gaseous mercury (TGM) concentrations as high as 7.5 ng/m3, a six‐time enhancement over background, were measured. The TGM was linearly correlated with CO (R2 = 0.805, where R is a 95% confidence level regression coefficient). Mercury was speciated as elemental mercury (>95%) and as mercury contained in the particulate fraction of the smoke. Emission factors (EF) were calculated from TGM and CO emissions and from a combustion efficiency of 0.9, adjusted for mercury contained in particulates, to yield an EF for total mercury of (113 ± 59) μg Hg per kilogram consumed fuel. The amount of mercury released from temperate forests in North America was extrapolated from our EF measurements and from National Interagency Fire Center estimates of burn areas. The average release for the period 1997–2001 is estimated to be 3.7 t Hg/yr, which is small relative to anthropogenic emissions. More significant is the contribution from fires in boreal forests (∼22.1 t Hg/yr) because of their much larger burn area. A measurement in smoke from a wheat stubble fire in Oregon showed mercury emissions as well, although with a lower EF. However, since agricultural waste burning is large globally, mercury from this source is also important in the global atmospheric cycling of mercury.

Some local environmental effects on mercury emission and absorption at a soil surface

The purpose of this study was to quantify effects of some local environmental variables on the soil surface exchanges of total gaseous mercury (TGM), under controlled conditions. A dynamic flux chamber with a Tekran® mercury analyzer was used to quantify TGM emissions from, and absorption by, a clean, fine sandy loam soil with very low mercury content inside of a building and in a low TGM environment, outside. Simultaneous measurements of mercury flux, air and soil temperatures, ozone concentration, humidity, soil moisture and solar radiation were made. Controlled applications of water were made to change soil H 2O content and measure the response of mercury flux. Air–soil exchanges were highly dependent on soil temperature ( r 2=0.78) and the mercury concentration gradient between the TGM in the soil pores and the ambient TGM above the soil surface ( r 2=0.98 for absorption and r 2=0.408 for emissions). Correlations with air temperature and ozone levels are explained by the relationships of these variables with soil temperature. No detectable correlation was found with solar radiation or humidity. Wet soil maintained higher rates of soil TGM emission and decreased soil absorption. Emissions increased with increasing soil H 2O, peaked at approximately field capacity, and then decreased slightly until saturation.