Changing Responses of PM 2.5 and Ozone to Source Emissions in the Yangtze River Delta Using the Adjoint Model.

China's industrial restructuring and pollution controls have altered the contributions of individual sources to varying air quality over the past decade. We used the GEOS-Chem adjoint model and investigated the changing sensitivities of PM 2.5 and ozone (O 3 ) to multiple species and sources from 2010 to 2020 in the central Yangtze River Delta (YRDC), the largest economic region in China. Controlling primary particles and SO 2 from industrial and residential sectors dominated PM 2.5 decline, and reducing CO from multiple sources and ≥C 3 alkenes from vehicles restrained O 3 . The chemical regime of O 3 formation became less VOC-limited, attributable to continuous NO X abatement for specific sources, including power plants, industrial combustion, cement production, and off-road traffic. Regional transport was found to be increasingly influential on PM 2.5 . To further improve air quality, management of agricultural activities to reduce NH 3 is essential for alleviating PM 2.5 pollution, while controlling aromatics, alkenes, and alkanes from industry and gasoline vehicles is effective for O 3 . Reducing the level of NO X from nearby industrial combustion and transportation is helpful for both species. Our findings reveal the complexity of coordinating control of PM 2.5 and O 3 pollution in a fast-developing region and support science-based policymaking for other regions with similar air pollution problems.