G3 (I) Sources and emissions

Global atmospheric emissions of mercury from human activities in 2005 were estimated to be approximately 1920 tonnes. Burning of fossil fuels (primarily coal) is the largest single source of emissions from human sources, accounting for about 45% of the total anthropogenic emissions. Artisanal/small-scale gold mining was responsible for about 18%, with industrial gold production accounting for an additional 5–6% of global emissions from human activities. Other mining and metal production activities are responsible for about 10% of global anthropogenic releases to the atmosphere. Cement production releases a similar amount. Emissions from waste incineration and product-use sources are more difficult to estimate. These emissions could be considerably higher than the generally conservative estimates of 150 tonnes included in the 1920 tonnes global estimate. Power plants are the largest single source in most countries with high mercury emissions, although in Brazil, Indonesia, Columbia, and some other countries (in South America, Asia and Africa in particular) artisanal/small-scale gold mining is the largest single source. Geographically, about two-thirds of global anthropogenic releases of mercury to the atmosphere appear to come from Asian sources, with China as the largest contributor worldwide. The United States of America and India are the second and third largest emitters, but their combined total emissions are only about one third of China’s.

Several measures are available for reducing mercury emissions; however, these measures differ with regard to emission control efficiency, cost, and environmental benefits obtained through their implementation. Measures that include the application of technology, such as technology to remove mercury from flue gases in electric power plants, waste incinerators, and smelters, are rather expensive compared with non-technological measures. In general, dedicated mercury removal is considerably more expensive than a co-benefit strategy, using air pollution control equipment originally designed to limit emissions of criterion pollutants, such as particulate matter, sulfur dioxide, or oxides of nitrogen. Substantial benefits can be achieved globally by introducing mercury emission reduction measures because they reduce human and wildlife exposure to methyl mercury. Although the reduction potential is greatest with the technological measures, technological and non-technological solutions for mercury emissions and exposure reductions can be carried out in parallel.

The United Nations Environment Programme (UNEP) has begun a process of developing a legally binding instrument to manage emissions of mercury from anthropogenic sources. The UNEP Governing Council has concluded that there is sufficient evidence of significant global adverse impacts from mercury to warrant further international action; and that national, regional and global actions should be initiated as soon as possible to identify populations at risk and to reduce human generated releases. This paper describes the development of, and presents results from, an inventory of anthropogenic mercury emissions in Australia which is now included in the UNEP database. Results indicate that: (1) The best estimate of total anthropogenic emissions of mercury to the atmosphere in 2006 was around 15 tonnes, compared with the most recent global emission estimate reports of about 34 tonnes/year; (2) Three sectors contribute substantially to Australian anthropogenic emissions: gold smelting (~50%), coal combustion in power plants (~15%) and alumina production from bauxite (~12%); (3) A diverse range of other sectors contribute smaller proportions of the emitted mercury. These include industrial sources (mining, smelting, and cement production) and the use of products containing mercury. It is difficult to determine historical trends in mercury emissions given the large uncertainties in the data. However, it is clear that use of products containing mercury is declining.

Emissions of mercury (broken down into elemental gaseous, reactive gaseous and particulate mercury) from natural sources such as vegetation, soils, water and fires, and from anthropogenic sources including large industial complexes, commercial–domestic sources and motor vehicles have been included in the inventory and spatial and temporal variations are accounted for.

This study shows the major results from the UNEP Project “Reducing mercury emissions from coal combustion in the energy sector” in China. We conducted literature review on the mercury and chlorine content of coal in China, analyzed the fate of mercury in coal-fired power plants, evaluated the mercury removal efficiencies of PM, SO₂ and NO_x control devices and developed the mercury emission inventory for coal-fired power plants in China in 2005. Based on the analyses of 177 coal samples, the average mercury content of raw coal samples is 0.17 mg/kg, ranging from 0.01 mg/kg to 2.25 mg/kg. The average chlorine content of raw coal samples is 269 mg/kg, ranging from 30 mg/kg to 3289 mg/kg.

The test results from 124 coal-fired power plants were collected from literature to analyze the mercury emission characteristics and the mercury removal efficiencies of air pollution control devices. For PC boilers, the mercury removal efficiencies of the PC+ESP, PC+ESP+WFGD, and PC+FF were 26%, 63%, and 76%, respectively.

Calculated by the probabilistic emission factor model, the best estimate for total mercury emissions from coal-fired power plants in China was 108.6 t in 2005. Preliminary analysis indicated that the SO₂ emission control policies taken during 2005~2010, including phasing-out of small units and installation of FGDs, had significant co-benefit of mercury reductions. Two pollution control scenarios, baseline scenario and policy scenario, were developed to forecast the future trend of mercury emissions.

The uncertainties of electricity demand, dependence on coal power, mercury content of coal as burned, and implementation of air pollution control policies would respectively result in high uncertainty in the mercury emission estimate. The trend of coal mining, coal transportation among provinces, and coal washing would also significantly affect the mercury emissions.

Stationary combustion sources are the major sources of mercury emission into the atmosphere. Mercury in combustion flue gas is speciated into three forms: elemental, oxidized, and particle-bound, the behavior of which differs with control devices and process configuration. In this study mercury speciation and emission concentration were measured and the mass balance in non-ferrous metals (zinc and lead) manufacturing facilities were carried out. With measured mercury concentration and flow rates at each ingoing and outgoing streams, mercury mass distributions were estimated. With several tests at the identical condition, the average mercury input, output rate and the mass distribution within the system were estimated. The tested facility was the combined zinc and lead manufacturing. Averaged mercury emission concentration at stack of zinc and lead manufacturing facilities were 0.9 µg Sm^-3 and 3.5 µg Sm^-3, respectively. In zinc manufacturing facility mercury was mainly speciated into elemental (59.6%), oxidized (16.0%), and particulate (24.4%) form. In lead manufacturing facility mercury speciations in elemental, oxidized and particulate form were 45.9%, 42.8%, 11.3% respectively. In an average, mercury recovery rate in the facility ranged 67 to 102%. The distributions of mercury in different streams were as: waste water sludge (53.1 to 62.4%), mercury recovery (7.1 to 29.7%), waste water (7.1 to 9.4%), zinc product (0.03%), cadmium product (0.01 %), released into the atmosphere (0.01%). Since major portion of mercury entered into the facility was distributed into waste water and sludge, proper attention is required for their treatment and disposal. Further, more comprehensive data are required to have more reliable distribution data and controlling mercury release into different media.

Many natural Hg pathways include a recycled component of anthropogenic material. Volcanoes are a primary emission source and historical archives such as ice-cores suggest large eruptions can release quantities of Hg similar to the present anthropogenic burden [1]. In order to better understand the role of volcanoes in the global mercury budget a number of field campaigns were carried out to evaluate the Hg/S ratios in volcanic gases. As observed in studies of background air Hg, gaseous elemental mercury (GEM) was the dominant form in the volcanic gases at the crater edge. While reactive gaseous mercury (RGM) and particulate mercury (Hg_(p)­) represent only a few % of the Hg present, concentrations of these species in volcanic air was several orders of magnitude higher than levels observed in background and industrial air studies. Recent modelling suggests that the large amount of reactive gases such as halogens released in volcanic plumes may lead to generation of RGM as the plume ages. This would have important implications in the fate of volcanic mercury. This process was investigated at Masaya Volcano, Nicaragua. This open vent basaltic volcano releases an estimated 7 tonnes of Hg to the atmosphere each year. Measurements were made to determine the RGM, GEM and Hg_(p) in the atmosphere at a number of distances from the crater edge under the volcanic plume. In addition the removal of mercury from the atmosphere was investigated via collection of vegetation samples and wet and dry deposition.

Hg/S ratios were determined and used in conjunction with the SO₂ volcanic flux to estimate Hg fluxes. Hg/S ratios in open vent emissions at Masaya and Etna were between 10^-6 and 10^-5. If representative of other volcanoes, these results suggest degassing of basaltic magma plays an important part of the global atmospheric Hg budget.

[1] Schuster, P.F. et al. Environmental Science & Technology, 36(11): 2303-2310 (2002).

High-altitude mountain glaciers are well suited as paleoarchives of natural and anthropogenic Hg emissions reflected both short-time events (volcanic eruptions, earthquakes) and prolongated impact of Hg contamination (natural emissions from ocean and soil, industrial and mining activities).Belukha glacier is especially interesting region for Hg study due to combination of natural and anthropogenic factors both on regional and global scales.

The aim of this study was to reconstruct past contributions of natural and industrial sources of atmospheric Hg contamination in the Siberian Altai during the last two centuries. Analysis was performed by atomic fluorescence spectrometry (“Mercur”, Analytik Jena, Germany) using US EPA 1631 method. Contamination-free methodology and optimization of instrumental parameters gives detection limit of Hg determination in ice and snow samples - 0.025 ng L^-1.

They are the first reliable data on Hg levels in snow and ice ever obtained for the Hg in Altai region. Hg concentrations in ice core range from 0,14 to 6,13 ng/l, excluded some peaks values attributed to volcanic eruption and, possibly, the earthquake in the Altai region. In pre-industrial times (before 1830) Hg concentrations are extremely low, average concentration is 0,65 ng/l. This level is comparable with values reported for remote areas such as Antarctica and Greenland. In the industrial time increased Hg concentrations are observed especially after 1940, with maximum concentrations from 1950 to 1980, when industrial activities in the Former Soviet Union were considerable. In industrial time concentration range and average Hg concentration are comparable with values reported for Mont Blanc glacier, whereas Hg concentrations in ice core of Upper Fremont glacier are much higher for all time intervals. Results of Hg determination in ice core from Belukha glacier comparing with Hg concentration in glacier ice from other locations are discussed in detail.

We propose approximate, but simple method of estimation regional constituent contribution using data from Greenland as background, and calculation of contribution from natural and industrial sources to atmospheric Hg contamination in the Siberian Altai using Belukha glacier’s paleoarchive data. Thus, the regional contribution on general Hg atmospheric contamination of Central Asia region is ~3,5 times more than global background one, the anthropogenic constituent of this contamination is 2 times grater than its natural component.

Currently, gaps still exist in the modeling of the overall mass-balance of snow Hg⁰ inputs and emissions in northern, temperate climates. To address this need, this study is quantifying and modeling the cumulative emission flux as a result of snow surface-to-air exchange of Hg⁰. Snow emissions of gaseous elemental mercury (GEM) (Hg⁰) are being measured using a modified Teflon fluorinated ethylene propylene (FEP) dynamic flux chamber (DFC) in an open field site in Potsdam, NY during the 2010-2011 winter season. The inlet and outlet of the DFC is paired with a Tekran® Model 2537A mercury vapor analyzer using a Tekran® Model 1110 two port synchronized sampler. Preliminary results indicate snow Hg⁰ emissions range from -13.5 ng m^-2 hr^-1 to 6.6 ng m^-2 hr^-1. The range of fluxes is greatest during sampling periods directly after snow deposition events that are followed by higher temperatures and solar radiation. Snow Hg⁰ emissions are strongly correlated with both temperature and solar radiation with Pearson product-moment correlation coefficients (PMCCs) ranging from 0.494 to 0.893 and from 0.289 to 0.723 respectively. Bi-weekly bulk precipitation and event surface-snow samples are also being collected in an effort to better characterize both long-term and immediate emissions.