Characteristics of particulate-bound mercury at typical sites situated on dust transport paths in China.

The concentrations and seasonal variations of PBM (particulate-bound mercury) were observed at four dust source sites (Duolun, Yulin, Hetian, and Tazhong), two megacities (Shanghai and Beijing), and an island site (Huaniao Island) to obtain the spatiotemporal characteristics of PBM in dust transport path from desert area in China to the East China Sea. The highest annual mean concentrations of PBM in TSP (PBMTSP) were observed at megacity sites, reaching 146.7 pg/m3 and 274.7 pg/m3 in Shanghai and Beijing attributed primarily to anthropogenic emissions, while 39.7 pg/m3, 67.3 pg/m3, 61.0 pg/m3, 23.5 pg/m3 and 43.6 pg/m3 over Duolun, Yulin, Hetian, Tazhong, and Huaniao Island, respectively. PBM concentrations were higher in winter and autumn, while lower in spring and summer due to the variation of meteorological conditions (especially temperature and wind speed) together with the emission sources. Enrichment factors (EFs) of PBMTSP and PBM2.5 reached 158 and 1452 in Beijing, showing the serious anthropogenic emissions impacted on PBM pollution in megacities, and the profound high level of EFs of mercury in sand dust source sites (17-64 for TSP and 38-252 for PM2.5), suggesting the obvious mixing effect of dust and anthropogenic aerosols in dust source areas. Human activities played a major role in the increase of PBM concentrations and the enrichment factors during the long-range transport of air mass in China. The significant anthropogenic mercury emissions in the dust source areas and their long-range transport driven by the East Asian Monsoon might impact on the ecological cycle of mercury and should be taken into the mercury inventories. Coal combustion and smelting contributed 52-94% to PBM over all three types of sampling sites, and mining operations were additional sources of PBM in Yulin. In the coastal area, sea salt is an important source of PBM, and shipping could also contribute a certain proportion to PBM pollution which shouldn't be ignored.