Sources of volatile organic compounds and policy implications for regional ozone pollution control in an urban location of Nanjing, East China

Abstract

Understanding the composition, temporal variability and source apportionment of volatile organic compounds (VOCs) is necessary for determining effective control measures to minimize VOCs and their related photochemical pollution. To provide a comprehensive analysis of VOC sources and their contributions to ozone (O3) formation in the Yangtze River Delta (YRD) – a region experiencing the highest rates of industrial and economic development in China – we conducted a 1-year sampling exercise using a thermal desorption GC (gas chromatography) system for the first time at an urban site in Nanjing (JAES site). Alkanes were the dominant group at the JAES site, contributing ∼53 % to the observed total VOCs, followed by aromatics (∼17 %), acetylene (∼17 %) and alkenes (∼13 %). We identified seasonal variability in total VOCs (TVOCs) with maximum and minimum concentrations in winter and summer, respectively. Morning and evening peaks and a daytime trough were identified in the diurnal VOC patterns. We identified VOC sources using positive matrix factorization (PMF) and assessed their contributions to photochemical O3 formation by calculating the O3 formation potential (OFP) based on the mass concentrations and maximum incremental reactivities of VOCs. The PMF model identified five dominant VOC sources, with highest contributions from diesel vehicular exhaust (34±5 %), followed by gasoline vehicular exhaust (27±3 %), industrial emissions (19±2 %), fuel evaporation (15±2 %) and biogenic emissions (4±1 %). The results of the OFP calculation inferred that VOCs from industrial and vehicular emissions were found to be the dominant precursors for OFP, particularly the VOC species of xylenes, toluene and propene, and top priority should be given to these for the alleviation of photochemical smog. Our results therefore highlight that priority should be given to limited VOC sources and species for effective control of O3 formation in Nanjing.