Assessment of background ozone concentrations in China and implications for using region-specific volatile organic compounds emission abatement to mitigate air pollution

Mitigation of ambient ozone (O-3) pollution is a great challenge because it depends heavily on the background O-3 which has been poorly evaluated in many regions, including in China. By establishing the relationship between O-3 and air temperature near the surface, the mean background O-3 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 O-3 in the polluted season (BOP) compared to the background O-3 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 O-3 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 O-3 to the observed total O-3 concentration in the design of anthropogenic precursor emission control strategies for the attainment of O-3 standards.

Automated summary

Mitigation of ambient ozone pollution is challenging, and the background ozone in China has been evaluated. The average background ozone mixing ratios during clean and polluted seasons were determined. Biogenic volatile organic compounds emissions were found to be the primary contributor to the increase in background ozone in the polluted season compared to the clean season. The background ozone continuously increased during the study period, while non-background ozone stopped increasing after a certain point. Reductions in anthropogenic VOC emissions are needed to reverse the current ozone levels.