China’s SO <sub>2</sub> emission reductions enhance atmospheric ozone–driven sulfate aerosol production in East Asia
Yu‐Chi Lin, Yan Zhao, Yan-Lin Zhang, Yihang Hong, Shohei Hattori, Syuichi Itahashi, Mei‐Yi Fan, Feng Xie, Zhu‐Yu Zhao, Mingyuan Yu, Fang Cao, Rongshuang Xu, Jianghanyang Li, Kimitaka Kawamura, M. H. Thiemens
Abstract
Reduction of China’s SO 2 emissions has been found to nonlinearly decrease the atmospheric sulfate (SO 4 2− ) aerosol concentrations in East Asia. Compared to Europe and North America, the lower effectiveness of SO 4 2− reduction in East Asia suggested much effects of “acidity-sensitive” feedback mechanisms in this high anthropogenic emission region, which have not been yet examined. In this work, we investigated these feedback mechanisms in East Asia through long-term measurements of the mass-independent oxygen-17 anomaly (Δ 17 O) in sulfate aerosols, machine learning and Community Multiscale Air Quality (CMAQ) model. As China’s emissions reduced, the atmospheric acidity decreased, enhancing the ozone-driven oxidation of S(IV) and production efficiency of sulfate formation. This explained the weaker declining SO 4 2− concentrations than SO 2 emissions. By the evidence from observed Δ 17 O in non-sea-salt sulfate (Δ 17 O-nss-SO 4 2− ) and CMAQ simulations, the highly enhanced contributions of S(IV)+O 3 to sulfate driven by reduced SO 2 emissions explained the low effectiveness of SO 4 2− reduction in East Asia. Additionally, the decreases of acidity by substantial NH 3 emissions are projected to continue until 2050, limiting SO 4 2− reduction effectiveness. Thus, we highlighted that global control of both SO 2 and NH 3 emissions are needed to efficiently mitigate the sulfate-related climate and pollution, especially in high NH 3 emission region, such as East Asia.