Gaseous elemental mercury concentration in atmosphere at urban and remote sites in China

An investigation of gaseous elemental mercury concentration in atmosphere was conducted at Beijing and Guangzhou urban, Yangtze Delta regional sites and China Global Atmosphere Watch Baseline Observatory (CGAWBO) in Mt. Waliguan of remote continental area of China. High temporal resolved data were obtained using automated mercury analyzer RA-915+. Results showed that the overall hourly mean Hg0 concentrations in Mt. Waliguan were 1.7+/-1.1 ng/m3 in summer and 0.6+/-0.08 ng/m3 in winter. The concentration in Yangtze Delta regional site was 5.4+/-4.1 ng/m3, which was much higher than those in Waliguan continental background area and also higher than that found in North America and Europe rural areas. In Beijing urban area the overall hourly mean Hg0 concentrations were 8.3+/-3.6 ng/m3 in winter, 6.5+/-5.2 ng/m3 in spring, 4.9+/-3.3 ng/m3 in summer, and 6.7+/-3.5 ng/m3 in autumn, respectively, and the concentration was 13.5+/-7.1 ng/m3 in Guangzhou site. The mean concentration reached the lowest value at 14:00 and the highest at 02:00 or 20:00 in all monitoring campaigns in Beijing and Guangzhou urban areas, which contrasted with the results measured in Yangtze Delta regional site and Mt. Waliguan. The features of concentration and diurnal variation of Hg0 in Beijing and Guangzhou implied the importance of local anthropogenic sources in contributing to the high Hg0 concentration in urban areas of China. Contrary seasonal variation patterns of Hg0 concentration were found between urban and remote sites. In Beijing the highest Hg0 concentration was in winter and the lowest in summer, while in Mt. Waliguan the Hg0 concentration in summer was higher than that in winter. These indicated that different processes and factors controlled Hg0 concentration in urban, regional and remote areas.