Two years measurement of speciated atmospheric mercury in a typical area of the north coast of China: Sources, temporal variations, and influence of regional and long-range transport

Abstract

Abstract Measurements of speciated atmospheric mercury (Hg) were conducted at the Changdao Island from October 2013 to July 2015 to characterize their seasonal and diurnal patterns, to identify the relationships between atmospheric Hg and meteorological parameters as well as trace gases, and furthermore to verify the potential sources of atmospheric Hg. There was a seasonal variation of gaseous elemental Hg (GEM) with the order of winter (2.87 ± 1.16 ng m−3), spring (2.58 ± 0.84 ng m−3), summer (2.25 ± 0.51 ng m−3), and fall (2.15 ± 0.39 ng m−3). The mean GEM value (2.52 ± 0.82 ng m−3) in the Changdao Island was about 1.7 times higher than that in the Northern Hemisphere, indicating that the Changdao and peripheral regions were polluted to some extent. Gaseous oxidized Hg (GOM) shows a clear seasonal variation with the highest value in summer (12.2 ± 9.4 pg m−3) and the lowest value in winter (4.6 ± 4.2 pg m−3). Moreover, the mean GOM concentration was significantly higher in daytime (11.9 ± 9.4 pg m−3) than in nighttime (6.3 ± 4.8 pg m−3) mainly due to the influence of solar radiation. In contrast, fine particulate Hg (HgP2.5) exhibited a distinct seasonal trend opposite to that of GOM. There was no significant difference between daytime HgP2.5 concentration (25.6 ± 23.9 pg m−3) and nighttime concentration (30.4 ± 31.2 pg m−3). The size distribution of HgP in PM10 was observed to be one-modal with the peak around the range of 1.1–2.1 μm in the winter, while it was bi-modal with a higher peak in the range of 1.1–2.1 μm and a lower peak in the range of 4.8–5.9 μm in other seasons. Generally, more than half of HgP was concentrated on fine particles (PM2.1). The temporal variation pattern of PM2.5/PM10 ratio was similar to those of HgP2.1/HgP10 or HgP3.3/HgP10. This further supports that HgP is mainly concentrated in fine particles. Correlation analysis shows that the GEM was positively correlated with SO2 and NO2. The average dry deposition flux of HgP10 was calculated to be 4.76 ng m−2 d−1 with a range of 0.86–13.46 ng m−2 d−1 based on all the size-fractionated HgP over the Changdao Island. This indicates that the dry deposition of HgP is an important part of atmospheric Hg deposition in coastal region because it happens all the time.