Strong ozone production in urban plumes from Beijing, China

Abstract

We report recent measurements of ozone (O₃) and related trace gases obtained in June–July 2005 in a mountainous area north of Beijing. Of the 39 days of observation, there were 13 days whose 1-hr O₃ mixing ratio exceeded 120 ppbv, with a maximum level of 286 ppbv, which is the highest reported value in open literature for China. Analysis of plume characteristics and air-mass back trajectories show the highest concentrations of O₃ (and other trace gases) were mainly due to emissions from the Beijing urban area. O₃ was strongly correlated with NO[sub y] with O₃-NO[sub y] regression slopes of 3–6 ppbv/ppbv in the six episodes examined. In contrast to some observations from North America, the positive O₃-NO[sub y] correlation in the Beijing plumes extended to NO[sub y] mixing ratios up to 55 ppbv, suggesting an important role of NO[sub x] in the formation of O₃ in Beijing. The very high concentrations of O₃ revealed in our study imply significant negative effects on vegetation and regional air quality. (See Article file for details of the abstract.)