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We performed incubation experiments using seawaters from representative marine environments of the eastern Asian seas to determine the mercury (Hg) available for photoreduction (Hgr(II)), to investigate the Hg redox reaction kinetics, and to explore the effect of environmental factors and water chemistry on the Hg redox chemistry. Results show that Hgr(II) accounted for a considerable fraction of total Hg (THg) (%Hgr(II)/THg: 24.90 ± 10.55%, n = 27) and positively correlated with THg. Filtration decreased the Hgr(II) pool of waters with high suspended particulate matter (SPM). The positive linear relationships were found between pseudo-first order rate constants of gross Hg(II) photoreduction (kr) and gross Hg(0) photo-oxidation (ko) with photosynthetically active radiation (PAR). Under the condition of PAR of 1 m mol m-2 s-1, the kr were significantly (p < 0.05) lower than ko (kr/ko: 0.86 ± 0.22). The Hg(0) dark oxidation were significantly higher than the Hg(II) dark reduction. The Hg(II) dark reduction was positively correlated to THg, and the anaerobic condition favored the Hg(II) dark reduction. Filtration significantly influenced the Hg photoredox chemistry of waters with high SPM. UVB radiation was important for both Hg(II) photoreduction and Hg(0) photo-oxidation, and the role of other wavebands in photoinduced transformations of Hg varied with the water chemistry. [ABSTRACT FROM AUTHOR]

Airborne particulate pollution is a critical environmental problem affecting human health and sustainable development. Understanding of the sources of aerosol particles is of extreme importance for regional air pollution control. Here we show that natural Si isotopic signature can be used as a new tool to elucidate the sources of fine particulate matter (PM2.5). Through the analysis of Si isotopic composition (δ30Si) of PM2.5 and its primary sources collected in a typical pollution region – Beijing, we recognized the direct source tracing ability of Si isotopes for PM2.5. The different primary sources of PM2.5 had different Si isotopic signatures. The δ30Si value of PM2.5 ranged from −1.99‰ to −0.01‰ and showed a distinct seasonal trend (isotopically lighter in spring/winter and heavier in summer/autumn). The variations in δ30Si of PM2.5 revealed that Si-isotopically light sources were important sources for Beijing's severe haze pollution and that coal burning was a major cause for the aggregating haze weather in spring/winter in Beijing. We also analyzed several typical haze events by using Si isotopic signatures. As the first study on the natural Si isotopes in the atmospheric environment, this study may reveal an important tool to advance the particulate pollution research and control. [ABSTRACT FROM AUTHOR]