Declines of gaseous element mercury concentrations at an urban site in eastern China caused by reductions of anthropogenic emission

Abstract

Long-term observations (June 2014 to June 2022) of atmospheric mercury (Hg) mass concentrations were conducted at an urban site in Nanjing, eastern China, together with other air pollutants. Throughout the sampling period, gaseous elemental mercury (GEM) exhibited a substantial decline from 5.41 ± 1.49 ng m−3 in 2014 to 2.17 ± 1.26 ng m−3 in 2022. The monthly mean concentrations of GEM displayed a significant downward trend, with a rate of 0.36 ng m−3 yr−1 (−7% yr−1). To identify the potential sources contributing to the observed GEM levels, positive matrix factorization (PMF) analysis was employed in conjunction with other relevant pollutants. The results revealed that the natural and anthropogenic emissions played comparable roles in shaping the measured GEM concentrations, with the reduction of coal combustion emissions being the primary driver behind the observed declines at this site. Furthermore, GEOS-Chem simulations suggested a substantial reduction of anthropogenic emissions in eastern China in recent years. This study highlights the decreasing trend of GEM concentrations in eastern China over the past decade, which is attributed to the combined efforts in air pollutant controls, resulting in the synergistic mitigation of Hg from the atmosphere.