Strong ozone production in urban plumes from Beijing, China

We report recent measurements of ozone (O 3 ) 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 O 3 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 O 3 (and other trace gases) were mainly due to emissions from the Beijing urban area. O 3 was strongly correlated with NO y with O 3 ‐NO y regression slopes of 3–6 ppbv/ppbv in the six episodes examined. In contrast to some observations from North America, the positive O 3 ‐NO y correlation in the Beijing plumes extended to NO y mixing ratios up to 55 ppbv, suggesting an important role of NO x in the formation of O 3 in Beijing. The very high concentrations of O 3 revealed in our study imply significant negative effects on vegetation and regional air quality.