Changes in Atmospheric Gaseous Elemental Mercury Concentrations and Isotopic Compositions at Mt. Changbai During 2015–2021 and Mt. Ailao During 2017–2021 in China
Xian Wu, Xuewu Fu, Hui Zhang, Kaihui Tang, Xun Wang, Hui Zhang, Qianwen Deng, Leiming Zhang, Kaiyun Liu, Qingru Wu, Shuxiao Wang, Xinbin Feng
Abstract
Abstract China is the largest contributor to the global total anthropogenic mercury (Hg) emissions. However, the trend in anthropogenic Hg emissions in recent years in China has not been effectively evaluated due to the lack of long‐term atmospheric Hg observations. This study documents the changes in atmospheric gaseous elemental mercury (GEM) concentrations and isotopic compositions at Mt. Changbai (MCB) in northeastern China during 2015–2021 and Mt. Ailao (MAL) in southwestern China during 2017–2021, and explores the potential factors controlling these changes. GEM concentrations showed continuous declines from 2015 to 2021 (−2.1 ± 0.6% yr −1 ) at MCB and from 2017 to 2021 (−4.0 ± 1.4% yr −1 ) at MAL. Accompanied with these GEM declines are positive shifts in δ 202 Hg (medians: from 0.42 to 0.46‰ at MCB and from 0.17 to 0.57‰ at MAL), and negative shifts in Δ 199 Hg (medians: from −0.17‰ to −0.21‰ at MCB and from −0.10‰ to −0.17‰ at MAL) and Δ 200 Hg values (medians: from −0.07‰ to −0.08‰ at MCB and from −0.03‰ to −0.05‰ at MAL) (at significant levels for Δ 199 Hg at MCB and δ 202 Hg and Δ 199 Hg at MAL). These changes were mainly caused by the decreases in regional anthropogenic emissions in the study areas. Based on a ternary mixing model with Δ 199 Hg and Δ 200 Hg as input, we estimate decline rates of 5.8 ± 2.8 and 4.8 ± 3.0% yr −1 for the regional anthropogenic GEM emissions in northeastern and southwestern China, respectively.