Ratios of Volatile Organic Compounds in Ambient Air of Various Cities of China

Abstract

Volatile organic compounds (VOC) ratios in urban atmosphere could provide important information on VOC data quality, sources, and options for removal processes. Based on seven VOC measurement datasets, useful VOC ratios were calculated using four methods, including orthogonal distance(ODR), linear regression, geometric mean, mean, and frequency distribution. Ambient levels of m,p-xylene and o-xylene from the seven datasets showed good correlation with r ranging from 0.975 to 0.997, and their ratios (m,p-xylene/o-xylene) were close, with values of 2.78-3.05, indicating therefore that the ratio of m,p-xylene/o-xylene could be used to evaluate the quality of ambient measurement data in urban atmospheres. In addition, ratios of toluene versus benzene (T/B) and propane versus ethane (P/E) in different cities were compared, to investigate VOC sources in China. The highest T/B ratios were found in Shanghai and Guangzhou City, with values of 2.37 and 1.78, respectively, higher than the result from a tunnel study (1.52), suggesting the important influence of paint and solvent use. The T/B value for Beijing City during summer was close to that from the tunnel study, while the T/B ratios for Chengdu, Beijing during winter, and Chongqing were lower, with values ranging from 0.744 to 1.36, suggesting possible influences from biomass burning and coal combustion. The P/E value in Guangzhou was 1.27, significantly higher than the range of 0.270 to 0.645 found in other cities. The OH exposure in different cities were calculated based on o-xylene/ethylbenzene (X/E), with values ranging from 2.70×1010 to 4.45×1010 molecule·cm-3·s.