Novel Method for Ozone Isopleth Construction and Diagnosis for the Ozone Control Strategy of Chinese Cities.

Ozone (O) isopleths describe the nonlinear responses of O concentrations to changes in nitrogen oxides (NO) and volatile organic compounds (VOCs) and thus are pivotal to the determination of O control requirements. In this study, we innovatively use the Community Multiscale Air Quality model with the high-order decoupled direct method (CMAQ-HDDM) to simulate O pollution of China in 2017 and derive O isopleths for individual cities. Our simulation covering the entire China Mainland suggests severe O pollution as 97% of the residents experienced at least 1 day, in 2017, in excess of Chinese Level-II Ambient Air Quality Standards for O as 160 μg·m (81.5 ppbV equally). The O responses to emissions of precursors vary widely across individual cities. Densely populated metropolitan areas such as Jing-Jin-Ji, Yangtze River Delta, and Pearl River Delta are following NO-saturated regimes, where a small amount of NO reduction increases O. Ambient O pollution in the eastern region generally is limited by VOCs, while in the west by NO. The city-specific O isopleths generated in this study are instrumental in forming hybrid and differentiated strategies for O abatement in China.