Tropospheric ozone climatology over Beijing: analysis of aircraft data from the MOZAIC program

Abstract

Abstract. Ozone (O3) profiles recorded over Beijing from 1995 to 2005 by the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) program were analyzed to provide a first climatology of tropospheric O3 over Beijing and the North China Plains (NCPs), one of the most populated and polluted regions in China. A pooled method was adopted in the data analysis to reduce the influence of irregular sampling frequency. The tropospheric O3 over Beijing shows a seasonal and vertical distribution typical of mid-latitude locations in the Northern Hemisphere, but has higher daytime concentrations in the lower troposphere, when compared to New York City, Tokyo, and Paris at similar latitude. The tropospheric O3 over Beijing exhibits a common summer maximum and a winter minimum, with a broad summer maximum in the middle troposphere and a narrower early summer (June) peak in the lower troposphere. Examination of meteorological and satellite data suggests that the lower tropospheric O3 maximum in June is a result of strong photochemical production, transport of regional pollution, and possibly also more intense burnings of biomass in Central-Eastern China. Trajectory analysis indicates that in summer the regional pollution sources from the NCPs, maybe mixed with urban plumes from Beijing, played important roles on the high O3 concentrations in the boundary layer, but had limited impact on the O3 concentrations in the middle troposphere. A comparison of the data recorded before and after 2000 reveals that O3 in the lower troposphere over Beijing had a strong positive trend (approximately 2% per year from 1995 to 2005) in contrast to a flat or a decreasing trend over Tokyo, New York City, and Paris, indicating worsening photochemical pollution in Beijing and the NCPs.