Ozone pollution is still considered a severe environmental problem in China despite the fact that great efforts have been devoted to monitoring and alleviating its impact by the Chinese government including the establishment of numerous observational networks. One of the issues most relevant to the design of emission reduction policies is to distinguish the O3 chemical regime. Here a method of quantifying the fraction of the radical loss versus NOx chemistry was applied to identify the O3 chemical regime inferred from the weekly pattern of atmospheric O3, CO, NOx, and PM10, which were monitored by Ministry of Ecology and Environment of China (MEEC). During spring and autumn, O3 and the total odd oxygen (Ox, Ox = O3 + NO2) weekend afternoon concentrations are both higher than the weekday values during 2015-2019 except in 2016, while CO and NOx weekend morning concentrations were generally both smaller than weekday values except 2017. Results from the calculated values of fraction of the radical loss by NOx chemistry relative to total radical loss (Ln/Q) suggested a volatile organic compound (VOC)-limited regime at this site in the spring of 2015-2019, as expected from the decreasing trend in NOx concentration and essentially constant CO after 2017. With respect to autumn, a shift from a transition regime during 2015-2017 to a VOC-limited regime in 2018 was found, which rapidly took place to a NOx-limited regime in 2019. No significant differences were detected in the Ln/Q values under different assumptions on photolysis frequencies both in spring and autumn mostly from 2015 to 2019, giving the same conclusion of determining the O3 sensitivity regime. This study develops a new method in determining the O3 sensitivity regime in the typical season in China and provides insight into efficient O3 control strategies in different seasons.
Keywords: Nitrogen oxides; Ozone; Sensitivity regime; Yangtze River Delta.
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