Characteristics of Volatile Organic Compounds in Nanjing and Suzhou, Two Urban Sites in the Yangtze River Delta, China

A field measurement study of volatile organic compounds (VOCs) was performed in January 2015 in the urban areas of two of the most important cities of the Yangtze River Delta: Nanjing and Suzhou. The objectives of this study included comparing the characteristics of VOC concentrations, comparing the impacts of emissions on VOCs, using species ratios to assess air mass age, and evaluating ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAP) in air masses. The VOC concentrations in Nanjing (34.6 +/- 5.8 ppbv) were higher than those of Suzhou (28.1 +/- 5.6 ppbv). The most abundant VOC measured was ethane (6.6 ppbv in Nanjing and 3.6 ppbv in Suzhou). Relevant analysis shows that motor vehicle emissions in Suzhou were dominant, whereas industrial emissions in Nanjing also contributed to VOCs. During rush hour, the VOC concentrations in Nanjing were the highest (35.3 ppbv). The T/B ratio (0.92-1.79) for the two sites was observed to be relatively low in the other studied cities, indicating the source impact of traffic emissions in the two sites. Indicators X/B (0.26-0.39) and X/E (0.33-0.66) also confirmed an aging air mass was transported at the two sampling sites. According to principal component factor analysis results, vehicle emissions (44.8% in Nanjing and 30.6% in Suzhou) were the most important contribution to the two sites. Industrial sites were not only likely to experience industrial emissions but were affected by traffic emissions. Using the OFP method, both sites showed the largest percentage of alkenes (59.9% in Nanjing and 62.0% in Suzhou). When comparing SOAP, both sites showed an absolute majority of aromatics (97.6% in Nanjing and 98.3% in Suzhou). To control the formation of O-3 and SOA in the two sites, it is necessary to reduce the concentration of alkenes and aromatics, respectively. By CPF analysis, pollutants transported from the SE and NE have significant effects on the Nanjing site. In the Suzhou, roads and industrial parks in the SE and S of Suzhou have significant impacts on the site.