Abstract
Abstract. Continuous measurements of atmospheric mercury concentration and speciation play a key role in identifying mercury sources and its behavior in the atmosphere. In this study, speciated atmospheric mercury including gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle-bound mercury (PBM) were continuously measured at Miyun, a rural site in Beijing, China, from December 2008 to November 2009. The average GEM, RGM and PBM concentrations were found to be 3.22 ± 1.74, 10.1 ± 18.8 and 98.2 ± 112.7 pg m−3, respectively, about 2–20 times higher than the background concentration of the Northern Hemisphere. The results indicated that atmospheric mercury concentrations in northern China were highly affected by anthropogenic emissions. The atmospheric mercury showed obvious seasonal variations, with the highest seasonal average GEM concentration 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 was observed, with peak levels in the late afternoon till midnight. Most of the high RGM concentration values occurred in the afternoon of all seasons due to the higher oxidation. The PBM concentration was higher in early morning of all seasons because of the the temperature inversion that increases in depth as the night proceeds. The ratio of GEM to CO indicates that residential 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 of local primary sources. The ratio of PBM to PM2.5 reveals that the air mass from the east and southwest of the site in spring and summer carries more atmospheric mercury. The HYSPLIT back-trajectory analysis indicated that the monitoring site is affected by local, regional and interregional sources simultaneously during heavy pollution episodes. The results from the potential source contribution function (PSCF) model indicate that the atmospheric transport predominantly from the northwest contributes to the elevated atmospheric mercury in winter and autumn, while the North China Plain (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.
Highlights
As it is a global pollutant, great attention has been paid to atmospheric mercury due to its long-range transport and toxicity
The three heavy pollution episodes indicate that the monitoring site is affected by local, regional and interregional sources simultaneously. Both the HYSPLIT results and the reactive gaseous mercury (RGM) / O3 ratios suggest that the mercury pollution in episode I is more impacted by the interregional sources in the Yangtze River Delta (YRD) region, in episode II it is more impacted by the regional sources in the North China Plain (NCP) region, and in episode III it is more impacted by the local sources
The 1 yr speciated mercury observation in Miyun from December 2008 to November 2009 indicated that the overall average gaseous elemental mercury (GEM), RGM and particle-bound mercury (PBM) concentrations are 3.22 ± 1.74, 10.1 ± 18.8 and 98.2 ± 112.7 pg m−3, respectively
Summary
As it is a global pollutant, great attention has been paid to atmospheric mercury due to its long-range transport and toxicity. Sheu et al (2002) conducted a 1 yr study in Stillpond, Maryland, and found the annual average GEM, RGM and PBM concentration to be 1.7 ± 0.5, 21 ± 22 and 42 ± 50 pg m−3, respectively. There is a lack of mercury monitoring data in rural areas with a regional background for typical heavily polluted regions in China such as the North China Plain (NCP) region. Most of these studies only measured atmospheric mercury, and did not simultaneously observe the concentrations of other air pollutants such as fine particles (PM2.5), carbon monoxide (CO) and ozone (O3), which could help to identify the emission sources and explain the atmospheric behavior of mercury. Based on the NOAA HYSPLIT model and the potential source contribution function (PSCF) model, the potential mercury sources and emission regions were analyzed, which helped to improve the understanding of atmospheric mercury outflow from China
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