Abstract
Abstract. A comprehensive measurement study of mercury wet deposition and size-fractionated particulate mercury (HgP) concurrent with meteorological variables was conducted from June 2011 to February 2012 to evaluate the characteristics of mercury deposition and particulate mercury in urban Nanjing, China. The volume-weighted mean (VWM) concentration of mercury in rainwater was 52.9 ng L−1 with a range of 46.3–63.6 ng L−1. The wet deposition per unit area was averaged 56.5 μg m−2 over 9 months, which was lower than that in most Chinese cities, but much higher than annual deposition in urban North America and Japan. The wet deposition flux exhibited obvious seasonal variation strongly linked with the amount of precipitation. Wet deposition in summer contributed more than 80% to the total amount. A part of contribution to wet deposition of mercury from anthropogenic sources was evidenced by the association between wet deposition and sulfates, as well as nitrates in rainwater. The ions correlated most significantly with mercury were formate, calcium, and potassium, which suggested that natural sources including vegetation and resuspended soil should be considered as an important factor to affect the wet deposition of mercury in Nanjing. The average HgP concentration was 1.10 ± 0.57 ng m−3. A distinct seasonal distribution of HgP concentrations was found to be higher in winter as a result of an increase in the PM10 concentration. Overall, more than half of the HgP existed in the particle size range less than 2.1 μm. The highest concentration of HgP in coarse particles was observed in summer, while HgP in fine particles dominated in fall and winter. The size distribution of averaged mercury content in particulates was bimodal, with two peaks in the bins of < 0.7 μm and 4.7–5.8 μm. Dry deposition per unit area of HgP was estimated to be 47.2 μg m−2 using meteorological conditions and a size-resolved particle dry deposition model. This was 16.5% less than mercury wet deposition. Compared to HgP in fine particles, HgP in coarse particles contributed more to the total dry deposition due to higher deposition velocities. Negative correlation between precipitation and the HgP concentration reflected the effect of scavenging of HgP by precipitation.
Highlights
Mercury (Hg) is a toxic global pollutant that can have serious negative effects on human health and the ecosystem via bioaccumulation and biomagnification of methylated mercury through the food chain in aquatic systems (Lindqvist, 1991; Schroeder and Munthe, 1998)
The mercury wet deposition calculated as the product of the concentration and amount of precipitation was 56.5 μg m−2 over 9 months
The large precipitation amount as well as mercury wet deposition and the lowest HgP dry deposition in summer possibly reflected the effect of scavenging by precipitation, indicated by every precipitation event followed by decreased HgP concentration at our site (Fig. 5)
Summary
Mercury (Hg) is a toxic global pollutant that can have serious negative effects on human health and the ecosystem via bioaccumulation and biomagnification of methylated mercury through the food chain in aquatic systems (Lindqvist, 1991; Schroeder and Munthe, 1998). Particulate mercury (HgP) is one of the major forms of mercury lost via wet and dry deposition (Sakata and Marumoto, 2002). Some measurements of HgP were conducted to estimate the dry deposition of mercury onto the particle surface (Fang et al, 2011b, 2011c; Wan et al, 2009b; Keeler et al, 1995; Chand et al, 2008). The size distribution of HgP changes due to physical and chemical processes including adsorption, nucleation, and other gas–particle partitioning mechanisms, ambient particle concentrations, and meteorological conditions (Kim et al, 2012). The mercury content in precipitation and atmospheric particles in nine size fractions from < 0.4 to 10 μm were monitored from June 2011 to February 2012 in urban Nanjing. To the best of our knowledge, this is the first comprehensive study of atmospheric mercury deposition and HgP in the YRD urban region
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