Characteristics of Volatile Organic Compounds in Megacity Shenzhen, China: Seasonal Variation, Temperature Dependence, and Source Apportionment

Volatile organic compounds (VOCs) are key precursors of secondary air pollutants. Elucidating the characteristics of ambient VOCs is important to make control strategies for secondary air pollution. In this study, continuous hourly measurements of 56 VOCs were made at both urban and rural sites in Shenzhen, China. The seasonal variation, temperature dependence, and source contributions of the VOCs were analyzed. Ambient VOC concentrations exhibited a winter maximum for anthropogenic species and a summer surge in biogenic species. Alkanes constituted the largest fraction of VOC concentrations at urban (52%) and rural (45%) sites, whereas alkenes and aromatics were predominant contributors to ozone formation. The concentrations of biogenic and anthropogenic VOCs all had strong dependences on changes in ambient temperature. The contribution of biogenic species to ozone formation increased with temperature and was much greater than that of anthropogenic species under high-temperature conditions. Four sources of VOCs, namely, vehicular exhausts, the petrochemical industry, regional transport, and volatile chemical products, were identified. Vehicular exhausts had the largest contribution (34%) at the urban site, while the petrochemical industry (41%) was the primary contributor at the rural site. The results underscore the necessity of region-specific mitigation measures targeting dominant VOC sources to alleviate secondary air pollution challenges in urban and rural environments.