Atmospheric mercury concentration and chemical speciation at a rural site in Beijing, China: implications of mercury emission sources

摘要

Continuous measurements of atmospheric mercury concentration and speciationplay a key role in identifying mercury sources and its behavior in theatmosphere. In this study, speciated atmospheric mercury including gaseouselemental mercury (GEM), reactive gaseous mercury (RGM) and particle-boundmercury (PBM) were continuously measured at Miyun, a rural site in Beijing,China, from December 2008 to November 2009. The average GEM, RGM and PBMconcentrations were found to be 3.22 ± 1.74, 10.1 ± 18.8 and98.2 ± 112.7 pg m?3, respectively, about 2–20 times higher thanthe background concentration of the Northern Hemisphere. The resultsindicated that atmospheric mercury concentrations in northern China werehighly affected by anthropogenic emissions. The atmospheric mercury showedobvious seasonal variations, with the highest seasonal average GEMconcentration in summer (3.48 ng m−3) and the lowest value in winter(2.66 ng m−3). In autumn and winter a diurnal variation of GEM wasobserved, with peak levels in the late afternoon till midnight. Most of thehigh RGM concentration values occurred in the afternoon of all seasons due tothe higher oxidation. The PBM concentration was higher in early morning of allseasons because of the the temperature inversion that increases in depth as thenight proceeds. The ratio of GEM to CO indicates thatresidential boilers play an important role in the elevation of GEM in winter.The ratio of RGM to O₃ could be an indicator of the contribution oflocal primary sources. The ratio of PBM to PM_2.5 reveals that the airmass from the east and southwest of the site in spring and summer carriesmore atmospheric mercury. The HYSPLIT back-trajectory analysis indicated thatthe monitoring site is affected by local, regional and interregional sourcessimultaneously during heavy pollution episodes. The results from thepotential source contribution function (PSCF) model indicate that theatmospheric transport predominantly from the northwest contributes to theelevated atmospheric mercury in winter and autumn, while the North ChinaPlain (NCP) region and the northern part of the Yangtze River Delta (YRD)region are the major source areas for mercury pollution in spring and summer.