Abstract
Abstract. In this study, the Community Multiscale Air Quality (CMAQ) modeling system is used to simulate the ozone (O3) episodes during the Program of Regional Integrated Experiments of Air Quality over the Pearl River Delta, China, in October 2004 (PRIDE-PRD2004). The simulation suggests that O3 pollution is a regional phenomenon in the Pearl River Delta (PRD). Elevated O3 levels often occurred in the southwestern inland PRD, Pearl River estuary (PRE), and southern coastal areas during the 1-month field campaign. Three evolution patterns of simulated surface O3 are summarized based on different near-ground flow conditions. More than 75% of days featured interactions between weak synoptic forcing and local sea-land circulation. Integrated process rate (IPR) analysis shows that photochemical production is a dominant contributor to O3 enhancement from 09:00 to 15:00 local standard time in the atmospheric boundary layer over most areas with elevated O3 occurrence in the mid-afternoon. The simulated ozone production efficiency is 2–8 O3 molecules per NOx molecule oxidized in areas with high O3 chemical production. Precursors of O3 originating from different source regions in the central PRD are mixed during the course of transport to downwind rural areas during nighttime and early morning, where they then contribute to the daytime O3 photochemical production. The sea-land circulation plays an important role on the regional O3 formation and distribution over PRD. Sensitivity studies suggest that O3 formation is volatile-organic-compound-limited in the central inland PRD, PRE, and surrounding coastal areas with less chemical aging (NOx/NOy>0.6), but is NOx-limited in the rural southwestern PRD with aged air (NOx/NOy<0.3).
Highlights
Tropospheric ozone (O3) is a secondary pollutant produced through a series of photochemical reactions involving mainly nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight
Model performance was assessed by comparing simulated O3, NOx, and non-methane hydrocarbons (NMHCs) concentrations with measurements from two super sites (GDEMC and Xinken) of the campaign and from Pearl River Delta (PRD) regional air quality monitoring networks
Elevated O3 levels were usually observed in the southwestern inland PRD, Pearl River estuary (PRE), and southern coastal areas, resulting from the intensive precursor emissions in the central PRD and the dominant northerly or easterly winds during October
Summary
Tropospheric ozone (O3) is a secondary pollutant produced through a series of photochemical reactions involving mainly nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. The O3 pollution in megacities and regional areas has been investigated recently by many studies (Evtyugina et al, 2006; Goncalves et al, 2009; Lei et al, 2007; Kimura et al, 2008; Yu et al, 2009; Chang, 2008; Ran et al, 2009; Wang et al, 2009), in which the topics addressed include O3 photochemical production, chemical sensitivity to precursors, roles of Published by Copernicus Publications on behalf of the European Geosciences Union. The Pearl River Delta (PRD) is one of the most urbanized and industrialized regions in southern China This area contains three megacities (Guangzhou, Shenzhen, and Hong Kong) and numerous medium and small cities, houses 4% of the total population of China, and produces about 19% of China’s gross domestic product each year. Photochemical smog has been one of the most severe air quality issues in the PRD, where surface O3 levels exceeding the national hourly standard of 200 μg/m3 (∼0.093 ppm) are frequently observed by air quality monitoring networks, especially in fall when northerly winds and clear sky conditions prevail (Wang et al, 2001, 2003; Zhang et al, 2007, 2008a)
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