Shifts of Formation Regimes and Increases of Atmospheric Oxidation Led to Ozone Increase in North China Plain and Yangtze River Delta From 2016 to 2019

Abstract China is confronting severe ozone (O 3 ) pollution although particulate matter reduced significantly, causing damages to public health and ecological systems. Here we utilized the comprehensive methods of ground‐level observations, satellite data, and source‐oriented chemical transport model to interpret O 3 variations throughout China from 2016 to 2019. A remarkably worsened trend of O 3 levels has been found both by observation and simulation in these years. Our results showed that the remarkable O 3 elevation was found in the North China Plain (NCP) and Yangtze River Delta (YRD) (maximum daily 8 hr average O 3 ∼60 ppb) with an annual increasing rate of 10%. In addition, O 3 formation regimes also changed in the NCP, where 4.9% grids shifted from VOC‐limited to transition regimes and 9.6% grids shifted from transition to NO x ‐limited regimes. The elevation of MDA8 O 3 was mainly attributed to the enhanced atmospheric oxidation capacity (AOC) in above regions. Particularly, the increasing rates of OH and HO 2 radicals (major oxidants) in NCP and YRD reached ∼15% and ∼5%, respectively. The comprehensive study of long‐term O 3 changes, formation regimes, and AOC based on a multimethod approach should be considered when designing O 3 control policies.