Variation characteristics and source differences of gaseous elemental mercury over four seasons in Qingdao: Influence of weather processes

Abstract

In the East Asian Monsoon Region, weather processes are important to the transport of pollutants in different seasons. The variation characteristics and sources of gaseous elemental mercury (GEM) and other pollutants were studied in typical air pollution processes throughout four seasons. The results showed that GEM concentrations in autumn, winter, spring and summer were 3.36 ± 3.61, 1.33 ± 0.62, 3.45 ± 2.31, and 2.20 ± 1.36 ng/m3, respectively. The concentrations of GEM in spring and autumn were higher than those in winter and summer. GEM daily variation was daytime-controlled throughout the four seasons. The concentration of GEM and pollutants was higher in polluted weather, which was controlled by the weather processes affected by the monsoon. The ratio of SO2/NO2 in winter and summer was 0.542 and 0.658, respectively, indicating that anthropogenic emissions such as coal-fired heating in winter and air-conditioning refrigeration in summer had a high contribution to GEM. In winter, high levels of pollutants, low GEM concentrations and the GEM/CO ratio were driven by the condensation of GEM under low temperature and the adsorption of GEM on more fine particles. The GEM concentration was higher during the daytime, and the temperature was significantly positively correlated with GEM throughout the four seasons (p < 0.01), indicating that mercury re-emissions from the Earth's surface were one of the main sources of GEM. Potential source contribution function analysis (PSCF) results showed that Shandong and Jiangsu provinces contributed more GEM than North China when autumn and winter pollution weather occurred. In spring, more southern regions such as Jiangxi, Zhejiang, Anhui, and Jiangsu contributed more GEM in polluted air. The adjacent southwestern region contributed more GEM in polluted weather in summer.