O3 photochemistry on O3 episode days and non-O3 episode days in Wuhan, Central China

Simultaneous field measurements of ozone (O3) and its precursors were conducted at an urban site (Zi Yang, ZY) and a suburban site (Huang Pi, HP) in August 2018 in Wuhan, China. The observation results revealed that the mean levels of nitric oxide (NO), nitrogen dioxide (NO2), carbon monoxide (CO) and non-methane hydrocarbons (NMHCs) were higher at ZY than those detected at HP, while the opposite trend was observed for O3 levels. Compared to non-O3 episode days, higher levels of O3 and its precursors (i.e. NMHCs, NO and CO) were observed on O3 episode days at both ZY and HP. A chemical box model was used to investigate the O3 photochemistry on O3 episode days and non-O3 episode days at ZY and HP, and the O3 production was found to be dominated by the reaction of HO2 + NO at the two sites. In terms of O3 destruction, OH + NO2 was the major contributor at ZY, while the highest contribution at HP was from the reaction of O(1D) + H2O. The net O3 production rates increased significantly from non-O3 episode days to O3 episode days at both ZY and HP, indicating increased O3 accumulation on O3 episode days. In addition, the model simulation indicated that O3 formation was controlled by volatile organic compounds (VOCs) at ZY, whereas O3 formation was cooperative controlled by VOCs and NO at HP. Overall, these findings can provide valuable information on formulating and implementing O3 control strategies in urban and suburban areas in China. •O3 photochemistry has been analyzed at an urban site (ZY) and a suburban site (HP) in Wuhan.•Regional atmospheric transport played an important role on the O3 concentrations at HP.•Higher photochemical reactivates were found on O3 episode days compared to those on non-O3 episode days in Wuhan.•O3 formation was AVOCs-limited at ZY while it was generally cooperatively controlled by AVOCs and NO at HP.