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Abstract. The spatial and temporal distribution patterns of mercury (Hg) in precipitation were investigated in the core urban areas of Chongqing, China. During the period from July 2010 to June 2011, total mercury (THg) and methyl mercury (MeHg) concentrations in precipitation were analysed from three sampling sites. Our results suggested that the volume-weight mean THg and MeHg concentrations in precipitation were 30.67 ng l −1 and 0.31 ng l −1 , respectively. The proportion of MeHg in THg ranged from 0.1 % to 7.6 % with a mean value of 1.3 %. THg and MeHg concentrations showed seasonal variations, while the highest THg value was measured in winter. Contrarily, the highest MeHg concentration was observed in autumn. Additionally, a geographically gradual decline of THg concentration in precipitation was observed from the downtown to the suburb, then to the controlled site in the city. 5 mm rainfall might be a threshold for the full wash-out capability. Rainfall above 5 mm may have a diluting effect for the concentrations of THg. Moreover, the current research implies that the coal combustion and motor vehicles could be the dominant sources for Hg in the precipitation.

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In order to explore the contributions of wet deposition and runoff formed by rainfall events to the water body mercury burden in Three Gorges Reservoir (TGR), we conducted a 1-year successive study on the deposition fluxes and runoff output characteristics of total mercury (THg) and methylmercury (TMeHg) in a typical small agricultural watershed in TGR areas. The results showed that the annual volume-weighted concentration (VWC) of THg and TMeHg was 18 and 0.23 ng L(-1), respectively. Particulate form was the main form of both THg and TMeHg, accounting for 61 % of THg and 59 % of TMeHg. The annual deposition fluxes of THg and TMeHg in rainfall were 13 ± 2.4 μg m(-2) year(-1) and 174 ± 52 ng m(-2) year(-1), respectively. The VWCs of THg and TMeHg in runoff were 10 ± 6.5 and 0.15 ± 0.15 ng L(-1). The annual output fluxes of THg and TMeHg to TGR from study area were 1.2 ± 0.73 μg m(-2) year(-1) and 17 ± 16 ng m(-2) year(-1), respectively.

The exchange of mercury (Hg) across the air-water interface is an important part of Hg biogeochemical cycle. Mercury fluxes across the air-water interface in paddy fields were measured by a Dynamic Flux Chamber (DFC) coupled with a Lumex ® multifunctional mercury analyzer RA-915 + at two sites (Chengjiang (CJ) and Caoshang (CS)) in Beibei, Chongqing, China in 2008. The results showed that mercury emission followed a power-law relationship with solar radiation and air temperature, and it increased exponentially with water temperature at both sites. Mercury emission was mainly influenced by the solubility of gaseous elemental Hg, photo-thermal effect, electron activity (Eh) and air Hg concentrations. Solar radiation made the greatest direct contribution to mercury emission during the daytime (0.80), with an 83.60% contribution, whereas at nighttime the water temperature (0.72) contributed to 71.65% of emissions. The temperature gradient between water and air might also influenced mercury emission across the air/water interface at nighttime. These findings suggest that paddy fields could act as a significant source of atmospheric mercury, and it can contribute significantly to the atmospheric mercury in a local region.