Abstract
Abstract. Guangzhou, one of China's megacities, is beset with frequent occurrence of high-concentration ozone events. In this study, online instruments were used to simultaneously monitor ozone, nitrogen oxides (NOx) and volatile organic compounds (VOCs) at GPACS (the Guangzhou Panyu Atmospheric Composition Station) of the China Meteorological Administration, from June 2011 to May 2012, in order to determine their characteristics, the effect of VOCs on ozone photochemical production and the relationship between VOC / NOx ratio and ozone formation. The results showed that during the observation period, the seasonal variation of ozone concentration was lower in spring and winter compared to summer and autumn, which is opposite that for VOCs and NOx. In terms of VOCs, aromatics had the largest ozone formation potential, among which toluene, xylenes, ethylbenzene, 1,2,4-trimethylbenzene and 1,3,5-trimethylbenzene were the most important species, with a total contribution of about 44%. As the VOC / NOx ratios were very high during high-concentration ozone events that occur all year round, we speculate ozone production was likely to be NOx-limited regime (12:00–16:00 LT) in Guangzhou. Further investigation based on numerical models is needed in the future to obtain more detailed and robust conclusions.
Highlights
Along with its rapid economic development and urbanization, the Pearl River Delta (PRD), whose major cities include but are not limited to Hong Kong, Guangzhou, Dongguan and Shenzhen, has become one of the most polluted areas in China (Chan and Yao, 2008)
This study aimed to explore the characteristics of volatile organic compounds (VOCs), nitrogen oxides (NOx) and ozone and to examine the possible seasonal and diurnal variations in ozone formation in the PRD based on 1 year of observational data for ozone and its precursors collected in Guangzhou, one of the PRD’s megacities
Seasonal variation in the concentration of ozone precursors was opposite to that of ozone concentration, with NOx concentrations being higher in spring and winter and VOC concentrations higher in winter compared to summer
Summary
Along with its rapid economic development and urbanization, the Pearl River Delta (PRD), whose major cities include but are not limited to Hong Kong, Guangzhou, Dongguan and Shenzhen, has become one of the most polluted areas in China (Chan and Yao, 2008). Unlike other regions in China, such as the region surrounding Beijing and the Yangtze River Delta region, where the main air pollutant is particulate matter (Zhao et al, 2011; Wang et al, 2012), high-concentration ozone events occur frequently in the PRD (Wang et al, 2009) due to its unique geographical location and climate, as well as a rapid increase in the emission of ozone precursors (volatile organic compounds (VOCs) and NOx) from industrial activities and motor vehicles. It has been found that VOCs and NOx have no linear relationship with ozone formation. Instead, their impact on ozone formation can be described by VOCor NOx-limited regimes (Zhang et al, 2004; Tie et al, 2007; Geng et al, 2008). Numerical simulations in polluted regions, such as Los Angeles in the 1980s, have shown ozone formation to be NOx-limited when the VOC / NOx ratio is greater than 8 : 1 for VOC expressed as the concentration of carbon atoms (Seinfeld, 1989), a finding which many re-
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