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The gaseous or particulate forms of divalent mercury (Hg II ) significantly impact the spatial distribution of atmospheric mercury concentration and deposition flux (FLX). In the new nested-grid GEOS-Chem model, we try to modify the Hg II gas-particle partitioning relationship with synchronous and hourly observations at four sites in China. Observations of gaseous oxidized Hg (GOM), particulate-bound Hg (PBM), and PM 2.5 were used to derive an empirical gas-particle partitioning coefficient as a function of temperature (T) and organic aerosol (OA) concentrations under different relative humidity (RH). Results showed that with increasing RH, the dominant process of Hg II gas-particle partitioning changed from physical adsorption to chemical desorption. And the dominant factor of Hg II gas-particle partitioning changed from T to OA concentrations. We thus improved the simulated OA concentration field by introducing intermediate-volatility and semi-volatile organic compounds (I/SVOCs) emission inventory into the model framework and refining the volatile distributions of I/SVOCs according to new filed tests in the recent literatures. Finally, normalized mean biases (NMBs) of monthly gaseous element mercury (GEM), GOM, PBM, WFLX were reduced from -33%-29%, 95%-300%, 64%-261%, 117%-122% to -13%-0%, -20%-80%, -31%-50%, -17%-23%. The improved model explains 69%-98% of the observed atmospheric Hg decrease during 2013-2020 and can serve as a useful tool to evaluate the effectiveness of the Minamata Convention on Mercury., (Copyright © 2022. Published by Elsevier B.V.)

This study developed an up-to-date and point-source-based inventory of mercury (Hg) releases to water in China by applying probabilistic release factors that combined industry removal efficiencies, reuse of reclaimed water, and receiving water types. In 2017, the national mercury release to water was estimated to be 50 (35-66) tons, in which 47%, 8%, 7%, and 25% were from nonferrous metal smelting, vinyl chloride monomer (VCM) production, coal-fired boilers, and domestic sewage, respectively. Approximately 95% of mercury was released to inland rivers, and the rest was discharged to lakes or coastal water. The significant sources were identified based on their mercury releases to water. The control of mercury release to water in China shall focus on zinc smelting plants, municipal sewage treatment plants, and the VCM production process. For zinc smelting plants, China can tighten the limit of mercury concentration in discharged wastewater and combine Hg-catcher device in traditional integrated treatment. For municipal sewage treatment plants and the VCM production process, promoting processes of Hg-free production can reduce mercury inputs at the source. Our study provides insights for other parties to identify the relevant sources of mercury release to water and to conduct control measures, so as to promote the global convention implementation.

Coal preparation is effective in controlling primary mercury emissions in coal combustion systems; however, the combustion of coal preparation byproducts may cause secondary emissions. The inconsistent coal preparation statistics, unclear mercury distribution characteristics during coal preparation, and limited information regarding the byproduct utilization pathways lead to great uncertainty in the evaluation of the effect of coal preparation in China. This study elucidated the mercury distribution in coal preparation based on the activity levels of 2886 coal preparation plants, coal mercury content database, tested mercury distribution factors of typical plants, and then traced the mercury flows and emissions in the downstream sectors using a cross-industry mercury flow model. We found that coal preparation altered the mercury flows by reducing 68 tonnes of mercury to sectors such as coking and increasing the flows to byproduct utilization sectors. Combusting cleaned coal rather than raw coal reduced the mercury emissions by 47 tonnes; however, this was offset by secondary mercury emissions. Coal gangue spontaneous combustion and the cement kiln coprocessing process were dominant secondary emitters. Our results highlight the necessity of whole-process emission control of atmospheric mercury based on flow maps. Future comprehensive utilization of wastes in China should fully evaluate the potential secondary mercury emissions.

China took aggressive air pollution control measures from 2013 to 2017, leading to the mitigation of atmospheric mercury pollution as a cobenefit. This study is the first to systematically evaluate the effect of five major air pollution control measures in reducing mercury emissions, the total gaseous mercury (TGM) concentration and mercury deposition flux (FLX) for unit emissions reduction. From 2013 to 2017, China's mercury emissions decreased from 571 to 444 tons, resulting in a 0.29 ng m -3 decrease in the TGM concentration, on average, and in a 17 μg m -2 yr -1 decrease in FLX. Ultralow emission renovations of coal-fired power plants are identified as the most effective emission abatement measure. As a result of this successful measure, coal-fired power plants are no longer the main mercury emitters. In 2017, the cement clinker sector became the largest emitter due to the use of less effective mercury removal measures. However, in terms of the mitigated TGM concentration and FLX levels per unit emission abatement, newly built wet flue gas desulfurization (WFGD) systems in coal-fired industrial boilers have become particularly effective in decreasing FLX levels. Therefore, to effectively reduce atmospheric mercury pollution in China, prioritizing mercury emissions control of cement clinkers and coal-fired industrial boilers is recommended.

• Ultra-low emission (ULE) retrofit significantly improves the overall Hg removal efficiency of devices. • The improvement of overall Hg removal after ULE retrofit mainly comes from the effect of dust removal devices. • Hg contents of both fly ash and gypsum are significantly lower than 25 mg/kg. • Large amount of Hg embodied in fly ash and gypsum calls for policies to guide the disposal of these wastes. China has applied the ultra-low emission technology in coal-fired power plants to control traditional air pollutants and to reduce Hg emissions synergically. In this study, we applied field experiment, model calculation, and literature review to evaluate the Hg control effect of ultra-low emission technology and the potential cross-media effect comprehensively. The dominant ultra-low emission technology significantly improves the atmospheric Hg removal efficiency from 75% to 87%. Such improvement mainly comes from the effect of dust removal devices. Based on the calculated distribution characteristic of Hg content of wastes, we find out that the improvement of Hg control effect of air pollution control devices significantly increase the Hg content of fly ash, which rises from 0.16 mg/kg to 0.33 mg/kg. However, the Hg content of gypsum decreases from 0.75 mg/kg to 0.51 mg/kg. Whether or not to carry out ultra-low emission retrofits, Hg contents of wastes from coal-fired power plants are overall lower than the limit of 25 mg/kg which is intended to be set as the limit for Hg-containing wastes. However, the embodied more than two hundreds of tons Hg in these wastes still require policies to guide the disposal of these wastes. [ABSTRACT FROM AUTHOR]