ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-12241-2011 Measurements of ozone and its precursors in Beijing during summertime: impact of urban plumes on ozone pollution in downwind rural areas Xu J. 1 2 3 Ma J. Z. 1 Zhang X. L. 3 Xu X. B. 1 Xu X. F. 3 Lin W. L. 1 Wang Y. 1 Meng W. 3 Ma Z. Q. 3 Chinese Academy of Meteorological Sciences, Beijing 100081, China Graduate University of Chinese Academy of Sciences, Beijing 100049, China Institute of Urban Meteorology, China Meteorological Administration, Beijing 100089, China 07 12 2011 11 23 12241 12252 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/12241/2011/acp-11-12241-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/12241/2011/acp-11-12241-2011.pdf

Sea-land and mount-valley circulations are the dominant mesoscale synoptic systems affecting the Beijing area during summertime. Under the influence of these two circulations, the prevailing wind is southwesterly from afternoon to midnight, and then changes to northeasterly till forenoon. In this study, surface ozone (O<sub>3</sub>), carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO<sub>2</sub>), nitrogen oxide (NO<sub>x</sub>) and non-methane hydrocarbons (NMHCs) were measured at four sites located along the route of prevailing wind, including two upwind urban sites (Fengtai "FT" and Baolian "BL"), an upwind suburban site (Shunyi "SY") and a downwind rural site (Shangdianzi "SDZ") during 20 June–16 September 2007. The purpose is to improve our understanding of ozone photochemistry in urban and rural areas of Beijing and the influence of urban plumes on ozone pollution in downwind rural areas. It is found that ozone pollution was synchronism in the urban and rural areas of Beijing, coinciding with the regional-scale synoptic processes. Due to the high traffic density and local emissions, the average levels of reactive gases NO<sub>x</sub> and NMHCs at the non-rural sites were much higher than those at SDZ. The level of long-lived gas CO at SDZ was comparable to, though slightly lower than, at the urban sites. We estimate the photochemical reactivity (<i>L</i><sub>OH</sub> and the ozone formation potential (OFP) in the urban (BL) and rural (SDZ) areas using measured CO and NMHCs. The OH loss rate coefficient (<i>L</i><sub>OH</sub> by total NMHCs at the BL and SDZ sites are estimated to be 50.7 s<sup>-1</sup> and 15.8 s<sup>-1</sup>, respectively. While alkenes make a major contribution to the <i>L</i><sub>OH</sub>, aromatics dominate OFP at both urban and rural sites. With respect to the individual species, CO has the largest ozone formation potential at the rural site, and at the urban site aromatic species are the leading contributors. While the O<sub>3</sub> diurnal variations at the four sites are typical for polluted areas, the ozone peak values are found to lag behind one site after another along the route of prevailing wind from SW to NE. Intersection analyses of trace gases reveal that polluted air masses arriving at SDZ were more aged with both higher O<sub>3</sub> and O<sub>x</sub> concentrations than those at BL. The results indicate that urban plume can transport not only O<sub>3</sub> but its precursors, the latter leading more photochemical O<sub>3</sub> production when being mixed with background atmosphere in the downwind rural area.

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