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

Ozone
(O3) isopleths describe the nonlinear responses
of O3 concentrations to changes in nitrogen oxides (NOX) and volatile organic compounds (VOCs) and
thus are pivotal to the determination of O3 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
O3 pollution of China in 2017 and derive O3 isopleths
for individual cities. Our simulation covering the entire China Mainland
suggests severe O3 pollution as 97% of the residents experienced
at least 1 day, in 2017, in excess of Chinese Level-II Ambient Air
Quality Standards for O3 as 160 μg·m–3 (81.5 ppbV equally). The O3 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 NOX-saturated
regimes, where a small amount of NOX reduction
increases O3. Ambient O3 pollution in the eastern
region generally is limited by VOCs, while in the west by NOX. The city-specific O3 isopleths
generated in this study are instrumental in forming hybrid and differentiated
strategies for O3 abatement in China.