Variability of PM2.5 and O3 concentrations and their driving forces over Chinese megacities during 2018-2020

Recently, air pollution especially fine particulate matters (PM_2.5) and ozone (O₃) has become a severe issue in China. In this study, we first characterized the temporal trends of PM_2.5 and O₃ for Beijing, Guangzhou, Shanghai, and Wuhan respectively during 2018-2020. The annual mean PM_2.5 has decreased by 7.82%-33.92%, while O₃ concentration showed insignificant variations by -6.77%-4.65% during 2018-2020. The generalized additive models (GAMs) were implemented to quantify the contribution of individual meteorological factors and their gas precursors on PM_2.5 and O₃. On a short-term perspective, GAMs modeling shows that the daily variability of PM_2.5 concentration is largely related to the variation of precursor gases (R = 0.67-0.90), while meteorological conditions mainly affect the daily variability of O₃ concentration (R = 0.65-0.80) during 2018-2020. The impact of COVID-19 lockdown on PM_2.5 and O₃ concentrations were also quantified by using GAMs. During the 2020 lockdown, PM_2.5 decreased significantly for these megacities, yet the ozone concentration showed an increasing trend compared to 2019. The GAMs analysis indicated that the contribution of precursor gases to PM_2.5 and O₃ changes is 3-8 times higher than that of meteorological factors. In general, GAMs modeling on air quality is helpful to the understanding and control of PM_2.5 and O₃ pollution in China.