Measurements of ozone and its precursors in Beijing during summertime: impact of urban plumes on ozone pollution in downwind rural areas

Abstract

Abstract. 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 3 ), carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO 2 ), nitrogen oxide (NO x ) 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 x 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 (L OH ) and the ozone formation potential (OFP) in the urban (BL) and rural (SDZ) areas using measured CO and NMHCs. The OH loss rate coefficient (L OH ) by total NMHCs at the BL and SDZ sites are estimated to be 50.7 s −1Correspondence to: J. Z. Ma (mjz@cams.cma.gov.cn) and 15.8 s −1 , respectively. While alkenes make a major contribution to the L OH , 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 3 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 3 and O x concentrations than those at BL. The results indicate that urban plume can transport not only O 3 but its precursors, the latter leading more photochemical O 3 production when being mixed with background atmosphere in the downwind rural area.

Reforms for a Cleaner, Healthier Environment in China

“…The results suggest that wide-ranging environmental pressures are not confined to cities, with a sizeable proportion of the villages surveyed failing to meet air and soil standards (Xiaoqing, 2012). This is consistent with studies showing significant pollution spillovers from cities into surrounding areas as well as high levels of pollution coming from rural areas themselves (Cao et al, 2006;Suthawaree et al, 2012;Xu et al, 2011;Yang et al, 2012). Likewise, rivers can transport pollution over large distances such that populations living in areas without high concentrations of heavily polluting industries may be exposed to upstream activities as well as environmental accidents which continue to pose a serious threat (He et al, 2012;Zhang and Zheng, 2012).…”

Ozone production in summer in the megacities of Tianjin and Shanghai, China: a comparative study

“…In the NCP region, most observations and analysis were performed at regional background sites or in the megacity of Beijing (e.g. Gao et al, 2005;Lin et al, 2008Lin et al, , 2009Lin et al, , 2011Tang et al, 2010;Lu et al, 2010;Xu et al, 2011a). In preparation for the 2008 Olympics, the relocation of old industrial facilities away from Beijing and other stringent emission restrictions were implemented to mitigate local air pollution.…”

Tropospheric NO<sub>2</sub> vertical column densities over Beijing: results of the first three years of ground-based MAX-DOAS measurements (2008–2011) and satellite validation

“…In order to investigate the photochemical pollution status as well as its formation mechanism and control policy, the concentrations of NO 2 near the ground, together with other chemical species and environmental parameters, were measured in Beijing during intensive field experiments over the past years, mostly using the chemiluminescence method (e.g. Tang et al, 2009;Lu et al, 2010;Wang et al, 2010b;Chou et al, 2011;Xu et al, 2011). Average NO 2 concentrations were estimated to be 30-40 ppbv for different seasons at the urban sites, with the hourly maximum reaching to 114 ppbv (Tang et al, 2009;.…”