Abstract
Abstract. Ozone (O3) concentrations in the lower troposphere (LT) over Beijing have significantly increased over the past 2 decades as a result of rapid industrialization in China, with important implications for regional air quality and the photochemistry of the background troposphere. We characterize the vertical distribution of lower-tropospheric (0–6 km) O3 over Beijing using observations from 16 ozonesonde soundings during a field campaign in April–May 2005 and MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft) over 13 days in the same period. We focus on the origin of LT O3 enhancements observed over Beijing, particularly in May. We use a global 3-D chemistry and transport model (GEOS-Chem CTM; GEOS – Goddard Earth Observing System) driven by assimilated meteorological fields to examine the transport pathways for O3 pollution and to quantify the sources contributing to O3 and its enhancements in the springtime LT over Beijing. Output from the Global Modeling Initiative (GMI) CTM is also used. High O3 concentrations (up to 94.7 ppbv) were frequently observed at the altitude of ~ 1.5–2 km. The CTMs captured the timing of the occurrences but significantly underestimated their magnitude. GEOS-Chem simulations and a case study showed that O3 produced in the Asian troposphere (especially from Asian anthropogenic pollution) made major contributions to the observed O3 enhancements. Contributions from anthropogenic pollution in the European and North American troposphere were reduced during these events, in contrast with days without O3 enhancements when contributions from Europe and North America were substantial. The O3 enhancements typically occurred under southerly wind and warmer conditions. It is suggested that an earlier onset of the Asian summer monsoon would cause more O3 enhancement events in the LT over the North China Plain in late spring and early summer.
Highlights
Tropospheric ozone (O3) is an effective greenhouse gas, especially in the upper troposphere (UT) (Lacis et al, 1990)
By tagging O3 originating in different source regions and conducting sensitivity simulations, we show that these O3 enhancements were mainly due to Asian anthropogenic pollution, while the impact of the European and North American emissions were significantly smaller
We evaluate the Global Modeling Initiative (GMI) chemistry and transport model (CTM) simulations with observations and show that current global models significantly underestimated the magnitude of these O3 enhancements
Summary
Tropospheric ozone (O3) is an effective greenhouse gas, especially in the upper troposphere (UT) (Lacis et al, 1990). Dufour et al (2010) reported that the lowertropospheric partial (0–6 km) column O3 in Beijing shows a sharp increase in late spring, with a maximum in May. High ground-level O3 in Beijing is caused by local anthropogenic emissions and by regional and longrange transport. To characterize the distribution and variability and quantify the sources of springtime lower-tropospheric O3 in Beijing, we analyze O3 vertical profiles measured during an ozonesonde sounding campaign, as well as aircraft measurements made by the MOZAIC program. Characteristics of the distribution and variability of springtime lower-tropospheric O3 in Beijing from ozonesonde observations and MOZAIC aircraft measurements in Sect.
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