Multimedia fate simulation of mercury in a coastal urban area based on the fugacity/aquivalence method

Due to intensive industrial production and living activities, urban areas are the main anthropogenic mercury (Hg) emission sources. After entering the environment through exhaust gases, wastewater or waste residues, Hg can migrate and transform among different environmental compartments in various species, such as elemental mercury (Hg0), divalent mercury (Hg2+) and methylmercury (MeHg). Studies have yet to report on the multimedia behaviors of Hg in urban areas due to the complexity of the processes involved. In this study, the atmospheric Hg emission in Dalian, a coastal city in Northeast China, was estimated by an anthropogenic emission inventory, and a Level III multimedia model was constructed based on the fugacity/aquivalence method to simulate the fate of Hg in air, water, soil, sediment, vegetation and film. The total annual atmospheric emission was 9.91 t, of which coal combustion and non-coal sources accounted for 70.1 % and 29.9 %, respectively. Atmospheric emission and advection were dominated by Hg0, and aquatic emission and advection were dominated by Hg2+. The migration of air-vegetation, vegetation-soil and soil-air were three important pathways of Hg in urban areas. The model was validated by collecting local soil and vegetation samples and regional air, seawater and sediment monitoring data. The scenario simulation indicated that the local load would decrease to different extents with a 21.0 % reduction in atmospheric Hg emission by implementing the "coal-to-gas" measures. Our developed model can characterize the fate of Hg in coastal urban areas and provide a reference for control strategies.

Determining an optimal control strategy for anthropogenic VOC emissions in China based on source emissions and reactivity

An evidence-based control strategy for emission reduction of VOC sources can effectively solve the regional PM2.5 and O3 compound pollution in China. We estimated the anthropogenic VOC emission inventory in China in 2018 and established a source profile database containing 129 sources based on localized detection and the latest research results. Then, the distribution of the ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAFP) for emission sources was analyzed. Moreover, priority control routes for VOC emission sources were proposed for different periods. Anthropogenic VOC emissions in China reached 27,211.8 Gg in 2018, and small passenger cars, industrial protective coatings, biomass burning, heavy trucks, printing, asphalt paving, oil storage and transportation, coking, and oil refining were the main contributors. Industrial protective coatings, small passenger cars, and biomass burning all contributed significantly to OFP and SOAFP. Priority in emission reduction control should be given to industrial protective coatings, small passenger cars, heavy trucks, coking, printing, asphalt paving, chemical fibers, and basic organic chemical sources over the medium and long term in China. In addition, the priority control route for VOC emission sources should be adjusted according to the variations in VOC emission characteristics and regional differences, so as to obtain the maximum environmental benefits.

Mapping anthropogenic emissions in China at 1 km spatial resolution and its application in air quality modeling

New challenges are emerging in fine-scale air quality modeling in China due to a lack of high-resolution emission maps. Currently, only a few emission sources have accurate geographic locations (point sources), while a large part of sources, including industrial plants, are estimated as provincial totals (area sources) and spatially disaggregated onto grid cells based on proxies; this approach is reasonable to some extent but is highly questionable at fine spatial resolutions. Here, we compile a new comprehensive point source database that includes nearly 100,000 industrial facilities in China. We couple it with the frame of Multi-resolution Emission Inventory for China (MEIC), estimate point source emissions, combine point and area sources, and finally map China's anthropogenic emissions of 2013 at the spatial resolution of 30″×30″ (~1 km). Consequently, the percentages of point source emissions in the total emissions increase from less than 30% in the MEIC up to a maximum of 84% for SO₂ in 2013. The new point source-based emission maps show the uncoupled distribution of emissions and populations in space at fine spatial scales, however, such a pattern cannot be reproduced by any spatial proxy used in the conventional emissions mapping. This new accurate high-resolution emission mapping approach reduces the modeled biases of air pollutant concentrations in the densely populated areas compared to the raw MEIC inventory, thus improving the assessment of population exposure.