China Played a Greater Role in Reducing the Deposition of Japan and Korea Than Themselves

China has been identified as a major contributor to transboundary air pollution in East Asia with a great impact on downwind countries (e.g., Japan and the Republic of Korea) through transboundary transport of air pollutants. While aggressive pollution controls have been conducted for the past decade, their benefit on Japan and Korea was insufficiently evaluated or recognized, particularly for atmospheric deposition with a direct effect on ecosystem health. Here, by combining available emission data, a chemical transport model, and a machine learning technique to estimate deposition patterns, we evaluate the impact of China's emission controls during 2010-2020 on the transboundary transport of oxidized nitrogen (OXN) and sulfur (S) and their deposition in Japan and the Republic of Korea. We find that the deposition in Japan and the Republic of Korea was declining faster than the local emissions of the corresponding precursor and that China has played a more important role in deposition reduction for the two countries than themselves. Transboundary flux of OXN and S from China to downwind areas declined swiftly at the initial stage of pollution controls, but would slow down afterward. Our analyses highlight the increasing importance of China in global environment improvement and the necessity of further strengthened controls of local emissions for downwind countries.