Mitigation of ambient ozone (O3) pollution is a great challenge because it depends heavily on the background O3 which has been poorly evaluated in many regions, including in China. By establishing the relationship between O3 and air temperature near the surface, the mean background O3 mixing ratios in the clean and polluted seasons were determined to be 35-40 and 50-55 ppbv in China during 2013-2019, respectively. Simulations using the chemical transport model (i.e., the Weather Research and Forecasting coupled with Chemistry model, WRF/Chem) suggested that biogenic volatile organic compounds (VOC) emissions were the primary contributor to the increase in the background O3 in the polluted season (BOP) compared to the background O3 in the clean season (BOC), ranging from 8 ppbv to 16 ppbv. More importantly, the BOP continuously increased at a rate of 0.6-8.0 ppbv yr-1 during 2013-2019, while the non-BOP stopped increasing after 2017. Consequently, an additional 2%-16% reduction in anthropogenic VOC emissions is required to reverse the current O3 back to that measured in the period from 2013 to 2017. The results of this study emphasize the importance of the relative contribution of the background O3 to the observed total O3 concentration in the design of anthropogenic precursor emission control strategies for the attainment of O3 standards.
Keywords: Background ozone; Biogenic volatile organic compounds; Nighttime ozone; Ozone-temperature relationship; WRF/Chem-MEGAN.
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