Assessing contributions of natural surface and anthropogenic emissions to atmospheric mercury in a fast-developing region of eastern China from 2015 to 2018

Mercury (Hg) is a global toxic pollutant that can be released into the atmosphere through anthropogenic and natural sources. The uncertainties in the estimated emission amounts are much larger from natural than anthropogenic sources. A method was developed in the present study to quantify the contributions of natural surface mercury emissions to ambient gaseous elemental mercury (GEM) concentrations through application of positive matrix factorization (PMF) analysis with temperature and NH3 as indicators of GEM emissions from natural surfaces. GEM concentrations were continuously monitored at a 2-hourly resolution at a regional background site in the Yangtze River Delta in eastern China during 2015–2018. Annual average GEM concentrations were in the range of 2.03–3.01 ng m−3, with a strong decreasing trend at a rate of -0.32±0.07 ng m−3 yr−1 from 2015 to 2018, which was mostly caused by reduced anthropogenic emissions since 2013. The estimated contributions from natural surface emissions of mercury to the ambient GEM concentrations were in the range of 1.00–1.13 ng m−3 on annual average, with insignificant interannual changes, but the relative contribution increased significantly from 41 % in 2015 to 57 % in 2018, gradually surpassing those from anthropogenic sources.