G4A (II) Atmospheric Mercury: Transport and deposition

Atmospheric transport and deposition of mercury can have deleterious effects on remote ecosystems, including the Adirondack Park in upstate New York, USA. Several studies have focused on the contamination of aquatic ecosystems within the park, but very few studies have examined the cycling of mercury through forests. One source of mercury inputs into forests is direct atmospheric uptake by leaves and needles and the subsequent addition of that mercury into the forest floor as leaves senesce. In this study we examine spatial patterns in the accumulation of mercury in foliage and soil across the Adirondack Park. Fifty plots that represent a range of elevation, species composition, and precipitation quantity were selected as study sites. Canopy foliage was collected from dominant species at all 50 sites within a two week period in August 2009. In addition, species relative basal area was measured and soil samples were collected from organic horizons at each plot. In the lab, all samples were analyzed for total mercury, percent carbon, percent nitrogen and leaf mass per area (LMA). Results show species-specific differences in foliar uptake of mercury with the lowest concentrations found in first-year growth conifer needles (white pine, Pinus strobus) and the highest concentrations found in black cherry (Prunus serotina). In this presentation we explore relationships between mercury and percent carbon, percent nitrogen, LMA and geographic variables such as latitude, longitude, and elevation. Using spatial analysis we developed maps of estimated foliar deposition of mercury for the Adirondack Park, and these data are combined with spatial models of wet deposition, dry deposition, and litterfall mass to produce a high-resolution model of total mercury deposition within the Adirondack Park. The relationship between total mercury deposition and soil mercury concentrations will be discussed.

Atmospheric deposition is a major source of loading of mercury (Hg) to terrestrial and aquatic ecosystems in several parts of the United States including Florida. While Hg deposition in Florida is influenced by local, regional and global emissions, it is of interest to examine, in particular, historical Florida deposition data in the context of changes in Florida Hg emissions over the past two decades to help inform the ongoing multi-stakeholder Florida statewide Hg Total Maximum Daily Load (TMDL) effort. To that end, this paper presents an analysis of temporal trends in anthropogenic Hg emissions and wet deposition in Florida to explore the presence and extent of statistically significant trends in these data. Various datasets compiled from state, regional and federal monitoring programs and other estimates during the 1995-2010 time period are analyzed to investigate whether trends in wet deposition follow trends in Florida emissions.

Historically, Hg has been emitted from a variety of anthropogenic sources in Florida including coal-fired electric generating units (EGUs), municipal and medical waste incinerators and industrial processes such as cement, steel, and pulp and paper. In this study, annual Hg emissions for Florida coal-fired EGUs in the 1990s and 2000s are estimated where possible using statistical correlations relating Hg removal and speciation to heat input measured by continuous emissions monitoring systems, coal mercury and chlorine content, and control technology. Hg emissions for some coal-fired EGUs in Florida are also obtained from stack measurements conducted in response to EPA’s 2009/2010 Information Collection Request (ICR). Historical Hg emissions for non-EGU source categories in Florida are obtained from a variety of sources including the National Emissions Inventories (NEI) for 1999 and 2005, the 2001 Clean Air Mercury Rule (CAMR), Florida DEP inventories and other emissions inventories compiled by various stakeholder groups. Historical Hg wet deposition data evaluated in the statistical analysis include measurements from the Southeastern Aerosol Research and Characterization Study (SEARCH) and the Mercury Deposition Network (MDN), measurements made during the Florida TMDL effort and other regional Hg monitoring studies in Florida.

Analyses of individual precipitation events show that mercury concentrations correlate with : 1) Storm type (higher in convective events than stratiform); 2)Rainfall depth; 3) Preciptation phase (rain vs. snow) and; 4) Season. Holmes et al. (2010) quantified the thunderstorm enhancement and dilution in large precipitation events; they also found that mercury concentration in rainwater correlated with radar reflectivity—a measure of precipitation intensity—but not cloud top height. These results suggest that rain and thunderstorm morphology affects mercury wet deposition, but the dynamical and microphysical causes are not yet known.

We examine the impact of thunderstorm dynamics and microphysics on mercury concentration and deposition using a cloud-resolving, non-hydrostatic model that includes detailed mechanistic treatments of cloud microphysics and scavenging. Simulations are initialized with model-derived vertical profiles of scavengable gaseous oxidized mercury that have been evaluated against aircraft and mountaintop observations. The simulations cover a range of atmospheric stability, shear, precipitable water, and cloud base height, which control thunderstorm morphology and reflect regional differences in storms across the US. We find intense convective storms expose their condensed water to higher GOM concentrations in the upper troposphere, compared to weaker storms. We evaluate the simulations against regional US differences in environment, storm morphology, and wet deposition.

With the development of industry in Chongqing, one important industrial city in southwest of China, more and more human activities increased the mercury emissions to atmosphere. What’s more, the special terrain of mountain and weather of no wind or breeze in chongqing lead mercury difficult to spread. The local atmospheric mercury pollution became more serious. Wet deposition has removal effects on the atmospheric mercury. To assess the importance of the atmospheric deposition, this paper measured methylmercury (MeHg) and total mercury (THg) concentrations collected in Nanan district (NA, city center), Beibei district (BB, suburb), Jinyun mountain (JY, exurb) in Chongqing between July, 2010 and February, 2011. Detectable MeHg concentrations were measured in all the precipitation samples at three sites and varied from 0.023 to 1.01ng/l. The lowest MeHg concentrations were observed in samples collected at JY where concentrations never exceeded 0.346ng/l, and the highest were observed at BB. Average MeHg concentrations in samples collected at August were highest and the lowest appeared at January. There were no statistically significant differences between concentrations in samples collected at three sites. THg concentrations in precipitation were generally between 8 to 60ng/l, most exceeding 60ng/l sampled in December and January when the temperatures were low. Generally, the range of MeHg proportion of THg was 0.04%-2.59%, with the exception of in three events at BB and two events at NA which the maximum reached 5.75%.

Peat cores have been used successfully as an environmental archive of an atmospheric deposition of elements of interest. However, most of these studies are predominantly focused on the peat cores from Europe and America. Here, a peat core from the Hongyuan peat in the eastern Tibetan Plateau, China is being used to reconstruct the atmospheric deposition of mercury (Hg) and other elements such as Ti, Pb, Cu, Zn, etc. The age dating of the ca. 500 cm long peat core showed the Hg accumulation for the past ca. 12,000 Cal. Years BP. The ash content calculated on the peat core showed that the peat is predominantly minerotrophic. However, other similar studies has shown that the minerotrophic peat could also be successfully used for the reconstruction of past atmospheric deposition of Hg. The initial measurement of Hg on obtained peat samples showed that the Hg concentration varies between few ng/g (e.g. ~ 20 ng/g) to several hundred (e.g. ~ 950 ng/g) indicating either the changes in sources or the changes in the deposition rates of Hg in the peat core. Therefore, further analysis of other elements such as Ti and Br which are indictor of soil dust and marine spray, respectively, would help to identify the enrichment of Hg either from natural sources such as marine spray, soil dust or anthropogenic input. Therefore, it is expected that the detailed analysis of Hg and its isotopes including other elements in the collected peat core would provide the Hg deposition rates in the South East Asia both from natural input and anthropogenic input for the entire Holocene.

Waste incineration, cement production, and productions of non-ferrous metals and steels are considered to be major anthropogenic sources of atmospheric mercury in Japan, although its trans-boundary transport from East Asian continent cannot be also negligible ^{1, 2)}. To evaluate spatial and temporal variations and contributions of emission sources for atmospheric mercury in Japan, we analyzed the nationwide survey data on total gaseous mercury (TGM) reported by Ministry of the Environment of Japan (referred to as “Environmental GIS” ³⁾) from 2001 to 2008. The annual mean TGM concentrations and their 98 percentile values were 2.1 ~ 2.3 ng m^-3 and 5.4 ~ 4.4 ng m^-3, respectively, and were both almost stable throughout the monitoring period. These values were higher than those observed in some rural and remote sites in East Asia (1.5 ~ 1.6 ng m^-3), suggesting enrichment by domestic and East Asian emissions ⁴⁾. Higher TGM concentrations tended to be detected in the monitoring stations located in large cities (Tokyo, Osaka and Fukuoka). The monitoring data are categorized based on area attributes: general environment (“G”), near emission sources (“E”) and roadside (“R”) ³⁾. The annual mean TGM concentrations for “E” were generally higher than those for “G”, although the standard deviations for “E” were also larger. The contribution of nearby emission sources was evaluated by analyzing the monitoring data of several stations categorized as “E” in relation to wind direction. The TGM concentrations tended to be higher at some sites when becoming downwind of emission sources, although the significantinfluences of emission sources could not be generally recognized. The contribution of trans-boundary transport from East Asia was assessed by analyzing the monitoring data for “G” in relation to Dust and Sand Storm (DSS) events. In 2002, 2006 and 2007, when the number of TGM data measured at the same time as observation of DSS at the neighboring sites was relatively large, the mean TGM concentration for these data was higher than that for the other data of “G”, suggesting trans-boundary transport of mercury from East Asian continent. We will further simulate the transport and behavior of atmospheric mercury in East Asia using atmospheric chemical transport models.

References: 1) Kida and Takahashi (2008), Global Environ., 13, 167-180 (in Japanese); 2) Jaffe et al. (2005), Atmos. Environ., 39, 3029-3038; 3) National Institute for Environmental Studies, http://www-gis.nies.go.jp/air/yuugaimonitoring/ (in Japanese); 4) Lin et al. (2010), Atmos. Chem. Phys., 10, 1853-1864.

The Asian continent is regarded as one of the most significant source regions in the world with regard to anthropogenic emissions to the atmosphere. Hence, there have been increased environmental concerns associated with the long-range transport of air pollutants caused by the marked increases in economic and population growth rates in China and other eastern Asian countries. Research over the last few decades has shown that various gaseous and particulate pollutants, including nonsea salt sulfate, nitrate, O₃, heavy metals, polycyclic aromatic hydrocarbons and black carbon, are transported from the Asian continent to Japan during winter and spring when airflows from the Asian continent are dominant. In this study, we examined the sources of mercury in aerosols at a site (Matsuura City, Nagasaki) on the Asian-continent side of southwestern Japan, which were inferred from the concentrations of related elements (Al, As, B, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sb, V and Zn) and the boron isotope ratio (d¹¹B). d¹¹B may be useful as a tracer of coal-burning plumes from the Asian continent. Aerosols were collected on quartz fiber filters using a high-volume air sampler in the second half (~2 weeks) of each month from April 2004 to March 2006. The Hg concentration in the aerosols generally showed a seasonal variation, namely, a decrease during summer and then an increase during winter. Factor analysis was applied to a data set of concentrations. Totally, 78.5% of the variance was explained by three factors, one of which had a high loading (0.73) of Hg along with those of As, B, Cd, Pb, Sb and Zn. Moreover, the d¹¹B of the aerosols decreased significantly during winter, and the estimated d¹¹B of B originating from nonsea salts showed negative values (approximately -17 – -27‰) during this season. Coal accounts for a major portion of the total primary energy supply in China. Coal enriches boron and generally represents negative d¹¹B values. These suggest that the emission of particulate Hg from industries, primarily from coal burning, in China is the most likely source.