Radical budget and ozone chemistry during autumn in the atmosphere of an urban site in central China

Abstract

Abstract The RO x (=OH + HO 2 + RO 2 ) budget and O 3 production at an urban site in central China (Wuhan) during autumn were simulated and analyzed for the first time using a UW Chemical Model 0‐D box model constrained by in situ observational data. The daytime average OH, HO 2 , and RO 2 concentrations were 2.2 × 10 6 , 1.0 × 10 8 , and 5.2 × 10 7 molecules cm −3 , respectively. The average daytime O 3 production rate was 8.8 ppbv h −1 , and alkenes were the most important VOC species for O 3 formation (contributing 45%) at this site. Our sensitivity test indicated that the atmospheric environment in Wuhan during autumn belongs to the VOC‐limited regime. The daily average HONO concentration at this site during the study period reached 1.1 ppbv and played an important role in the oxidative capacity of the atmosphere. Without the source of excess HONO, the average daytime OH, HO 2 , RO 2 , and O 3 production rates decreased by 36%, 26%, 27%, and 31% respectively. A correlation between the HONO to NO 2 heterogeneous conversion efficiency and PM 2.5 × SWR was found at this site; based on this relationship, if the PM 2.5 concentration met the World Health Organization air quality standard (25 µg m −3 ), the O 3 production rate in this city would decrease by 19% during late autumn. The burning of agricultural biomass severely affected the air quality in Wuhan during summer and autumn. Agricultural burning was found to account for 18% of the O 3 formation during the study period. Our results suggest that VOC control and a ban on agricultural biomass burning should be considered as high‐priority measures for improving the air quality in this region.