4c: Anthropogenic emissions: Monitoring and analysis to support mitigation

An assessment of current and future emissions of mercury worldwide is presented on the basis of results obtained during the duration of the EU GMOS (Global Mercury Observation System) project. Emission estimates for mercury were prepared with the main goal of applying them in models to assess recent (2013) and future (2035) air concentrations, and atmospheric deposition trends of this contaminant. In this way, the project contributed to monitoring the implementation of international agreements on mercury emission reductions and its impacts on environmental and human health.

The combustion of fossil fuels (mainly coal) for energy and heat production in power plants and in industrial and residential boilers, as well as artisanal and small-scale gold mining, are the major anthropogenic sources of mercury emissions to the atmosphere at present. These sources account for between 37% and 25% of total anthropogenic mercury emissions globally, estimated to be about 2000 t. Emissions in Asian countries, particularly in China and India, dominate the total emissions. The current estimates of mercury emissions from natural processes (primary mercury emissions and re-emissions), including mercury depletion events, were estimated to be 5207 t annually, which represents nearly 70% of the global mercury emission budget. Oceans are the most important source (36 %), followed by biomass burning (9 %). A comparison of the 2035 anthropogenic emissions estimated for three different scenarios with current anthropogenic emissions indicates a reduction of these emissions in 2035 of up to 85% for the best-case scenario.

Two global chemical transport models have been used within the GMOS project for the evaluation of future mercury pollution levels considering future emission scenarios. Projections of future changes in mercury deposition on a global scale simulated by these models for three anthropogenic emissions scenarios of 2035 indicate a deposition decrease of up to 50% in the Northern Hemisphere, and up to 35% in Southern Hemisphere for the best-case scenario.

A discussion on mitigation measures that need to be employed in order to achieve the 2035 emission reduction targets is also presented

We have presented atmospheric Hg emissions in China for the year 2020 and 2030 in this study. We find that atmospheric Hg emissions are projected to be similar as the emissions in 2010 (approximately 539 t) under business as usual scenario. This indicates that the Hg removal by the progressive end-of-pipe pollution control measures will be offset by the Hg input from increased energy consumption and products production. By using the stringent control technologies, atmospheric Hg emissions can be reduced by up to 76.9% in 2030 at the accelerated pollution control technology scenario. Future emission scenarios imply different mitigation options for the convention-regulated sectors. Current legislations and progressive pollution control (eg., dust collection, desulfurization and denitration measures) will be the primary mitigation options for controlling emissions from coal-fired power plants, coal-fired industrial boilers, and nonferrous metal smelting, which will reduce 87%, 55% and 74% of current emissions (compare to 2010), respectively. Large-scale deployment of dedicated Hg removal technologies (eg., activated carbon injection and Boliden-Norzink technology) will aid to additional 2%, 35% and 15% of Hg reductions in these three sectors, respectively. For cement production, unless the stringent control measures (eg., dust shuttling) are fully applied, Hg emissions will increase by up to 22% in 2030 under the business as usual scenario. For municipal solid wastes incineration sectors, due to the sharp increase of incinerated solid wastes, Hg emissions will increase to 5.7-11.7 t in 2030, all larger than the emissions of 0.7 t in 2010. Thus, stringent control measures should be used in this sector.

Due to rapid industrialization and urbanization in East Asia, the frequent occurrence of haze or smog is a growing concern. Particulate matter (PM), and especially, PM2.5, a transboundary atmospheric pollutant, is of particular interest as it has negative impacts on human health. Deciphering its origins and contributing sources is therefore vital for establishing effective reduction policies. We collected weekly PM2.5 samples from an urban (Seoul) and a rural (Baengnyeong Island) area in Korea from January 2014 to July 2016 and analyzed the isotopic compositions of PM2.5, including 13C, 15N, 34S- SO42-, 15N-NO3-, 18O-NO3-, and 15N-NH4+, as well as particle-bound mercury (PBM). The mean concentrations of PBM were 36 ± 34 pg m−3 at the Seoul site and 12 ± 11 pg m−3 on Baengnyeong Island. Obvious seasonal PBM variations were observed at both sites, as concentrations were higher in winter than in summer. At Baengnyeong, PBM concentrations showed good positive correlations with OC, EC, and Pb concentrations, as well as the isotopic compositions of 13C, 34S- SO42-, and 15N-NO3-, whereas 15N-NH4+ showed negative correlations with PBM. The stable isotopic compositions are expected to be more enriched with 13C, 34S-SO42-, and 15N-NO3- and depleted of 15N-NH4+ when PM2.5 arises from coal combustion rather than from vehicle and biogenic emissions. Thus, the positive correlations of 13C, 34S-SO42-, and 15N-NO3- with PBM and the negative correlations of 15N-NH4+ with PBM imply that the major PBM source during winter in Baengnyeong is coal combustion.

Measurement of ambient mercury concentrations has been undertaken over an extended period at a site in the Hunter Valley north of Sydney proximate to both coal fired power generation and mining activities. Mercury measurement at the site has been supplemented by measurements of SO2, particulates and meteorology. Results for more than 24 months of sampling have confirmed that mean annual ambient mercury levels are generally low by international comparison and in the range 0.8 -1.0 ng/m3. However, on occasion, higher level peaks of up to 2.5 ng/m3 and mercury depletion events have been observed. Some examples of these events and their possible causes are discussed. As the coal fired power stations are the only significant source of SO2 in the region, the contribution of this source to mercury concentrations can be determined by examining the relationship between SO2 and total gaseous mercury (TGM). However there is a poor correlation between high SO2 and TGM during the period suggesting that the power stations are not the source of the peak values of TGM. In fact SO2 rises sharply and falls rapidly again with elevated levels seldom extending beyond several hours, and mostly occurring from late morning to mid-afternoon under convective conditions when the plume from the stations reaches the ground. By contrast the high mercury concentrations appear to be associated with drainage flows following nocturnal inversion events; where low levels of atmospheric mixing enhanced by low wind speeds create stable conditions minimising dispersion and leading to the build up of higher levels of TGM trapped below the boundary layer height. The source of mercury emission for these events is the subject of on-going research.

A reclamation program in the abandoned Hg world-class mining district of Abbadia San Salvatore (Tuscany, central Italy), whose activity ceased in 1976, has started with a geochemical characterization of surface and ground waters, soil, air and mining structures. In 2008, the former owner (ENI Ltd. - AGIP Division) transferred properties and mining concessions to the Municipality of Abbadia San Salvatore that now is the responsible of the reclamation process. The mining activities ended up without any clean-up strategy. The metallurgical plants and tailings, with huge piles of calcines and roasting products where relevant amounts of metallic mercury are still present, were abandoned. Mine adits and shafts were closed, leaving flowing drainage tunnels and two unsealed chimneys to disperse a natural flow of CO2-rich gas discharge. This occurred without strict environmental regulations that became State laws in 1999. Recently, the mining areas were divided in 6 sub-areas (lots) in accordance with the local Environmental Protection Agency, on the basis of the type of operations to be performed for reclaiming the mining area. Lot 6 represents the most critical one, being the site where cinnabar was managed and roasted to produce liquid mercury after condensation processes. The other lots are characterized by workers and managers buildings and then, less affected by Hg contamination.

In this work, we present an update of the reclamation activities, providing new original data on the different geological and anthropogenic materials included in the former mining concession. Most these compartments are indeed affected by Hg concentrations that are well above the threshold concentration limits for mercury according to regulations issued by the Tuscany Region for recovering abandoned mining areas. Consequently, operational activities are presently going on to minimize the presence of mercury in the building materials and edifices (including the air), soils and terrains and surface and underground waters. Actions, criticalities and perspectives for the remediation process, which is focused on environmental restoration to achieve a historic museum and mining park, are highlighted.The results are useful to the workers who are going to operate in the mining areas during the operational activities of remediation.

Atmospheric mercury is a global concern because of its high toxicity, transboundary transport and its ability to biomagnify and bioaccumulate. It causes great harm to the human health, ecosystem and environment. It has been extensively studied in different parts of the world, but very few studies are available from India. Therefore, this study is an attempt to report mercury levels in Respirable Suspended Particulate Matter (PM10-Hg) and to identify its potential sources of contribution through backward trajectories at a rural site (Mahasar, Haryana) located ~130 km SW of New Delhi. In this study, we have also measured the seasonal variability of PM10-Hg. The study was carried out during December 2014 to June 2015. Mercury was determined using differential pulse anodic stripping voltammetry through standard addition methods. The mean (± standard deviation) concentrations of PM10-Hg during winter and summer seasons were 1.01 ± 0.3 ng/m3 and 0.32 ± 0.2 ng/m3 respectively. The higher concentrations of PM10-Hg were observed in winter, possibly due to increased emissions from the combustion sources, reduced mixing heights, transportation from other regions and less precipitation. At the study site, burning of biofuels such as wood and cow dung cake for cooking and heating purposes is increased many folds during winter as compared to summer. Lower concentrations of PM10-Hg during summer might be due to increased mixing heights as well as due to the scavenging effect as some light to heavy rain events were also observed during summer time sampling. In order to find out the contribution of mercury from other source regions and the transport pathways of air masses arriving at our observation site, five-days backward airmass trajectories at three heights (500m, 800m and 1000 m) above the ground level were calculated using HYSPLIT model of NOAA. The analysis of these trajectories revealed that during peak winters, air masses were coming from the south and south-east regions of India which have been reported as the hot spots of coal deposits and coal mining activities as well as burning of coal in industries and thermal power plants. Probably, due to this reason, PM10-Hg was higher during winters, apart from local source contributions. Backward trajectory analysis revealed that PM10-Hg concentrations were lower when the airmasses were arriving from western India, Arabian Sea and Middle-East regions. The interesting results of this study need further comprehensive monitoring of different forms of mercury too.

Atmospheric mercury species, including gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particulate bound mercury (PBM), trace pollutants (including ozone, SO2, CO, NO, NOY and black carbon), and meteorological parameters have been continuously monitored since 2007 at an Atmospheric Mercury Network (AMNet) site in Grand Bay, Mississippi. Average hourly mercury concentrations and standard deviations were 1.40±0.23 ng m-3 for GEM, 5.9±11.4 pg m-3 for GOM, and 5.0±10.8 pg m-3 for PBM. Diurnal variation of GEM shows a slight increase in GEM concentration during the morning, likely due to downward mixing of higher concentrations from the residual layer. Seasonal variation of GEM shows higher levels in winter and spring. Diurnal variations of both GOM and PBM show peaks in the afternoon likely due to photochemical oxidation of GEM. Seasonally, PBM measurements exhibit higher levels in winter and spring and low levels in summer, while GOM measurements show high levels in early summer and late fall and low levels in winter. These data were analyzed using HYSPLIT back trajectories in order to develop source-receptor relationships for mercury species in this coastal environment. Trajectory frequency analysis shows that high mercury concentrations were generally associated with air masses arriving from areas with high mervery emissions, while low mercury levels were largely associated with trajectories passing through relatively clean areas. This study indicates that the receptor site, which is located in a coastal environment on the Gulf of Mexico, experienced impacts from mercury sources that are both local and regional in nature.