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 NOy with O-3- NOy regression slopes of 3 - 6 ppbv/ ppbv in the six episodes examined. In contrast to some observations from North America, the positive O-3- NOy correlation in the Beijing plumes extended to NOy mixing ratios up to 55 ppbv, suggesting an important role of NOx 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.