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China is confronting severe ozone (O3) 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 O3 variations throughout China from 2016 to 2019. A remarkably worsened trend of O3 levels has been found both by observation and simulation in these years. Our results showed that the remarkable O3 elevation was found in the North China Plain (NCP) and Yangtze River Delta (YRD) (maximum daily 8 hr average O3 60 ppb) with an annual increasing rate of 10%. In addition, O3 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 NOx-limited regimes. The elevation of MDA8 O3 was mainly attributed to the enhanced atmospheric oxidation capacity (AOC) in above regions. Particularly, the increasing rates of OH and HO2 radicals (major oxidants) in NCP and YRD reached 15% and 5%, respectively. The comprehensive study of long-term O3 changes, formation regimes, and AOC based on a multimethod approach should be considered when designing O3 control policies.
Wang et al. (Fri,) studied this question.