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Origin of Springtime Ozone Enhancements in the Lower Troposphere Over Beijing: In Situ Measurements and Model Analysis

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Monday, December 2, 2013

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This is a past event.

Hongyu Liu

Ozone concentrations in the lower troposphere (LT) over Beijing have significantly increased over the past two decades as a result of rapid industrialization in China, affecting regional air quality and photochemistry of the background troposphere. We characterize the vertical distribution of lower-tropospheric (0-6km) ozone over Beijing using observations from 16 ozonesonde soundings made during a field campaign in April-May 2005 and MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft) aircraft measurements over 13 days in the same period. A particular focus is placed on the origin of the LT ozone enhancements. We use a global 3-D chemical transport model (GEOS-Chem CTM) to interpret those characteristics, examine the transport pathways for ozone pollution, and quantify the sources contributing to ozone and its enhancements in the springtime LT over Beijing. High ozone concentrations (up to 94.7 ppbv) were frequently observed at the altitude of ~1.5-2km. The model captured the occurrences but significantly underestimated the magnitude of these ozone enhancements. Model simulations and a case study show that ozone produced in the Asian troposphere (especially due to Asian anthropogenic pollution) made major contributions to the observed ozone enhancements. Contributions from European and North American troposphere and anthropogenic pollution thereof reduced during these events, compared to those days without ozone enhancements. These ozone enhancements typically occurred under southerly wind and warmer conditions, and their occurrence frequency in late spring appears to be related to the onset of Asian summer monsoon. The impact of Eurasian biomass burning on the LT ozone over Beijing during spring will also be discussed with the Global Modeling Initiative (GMI) CTM simulations. The results have important implications for predicting the air quality of the North China Plain as well as understanding the interannual variability of springtime tropospheric ozone in Northeast Asia.

Host: Shiliang Wu

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