VOCs sources and roles in O3 formation in the central Yangtze River Delta region of China

Abstract

Surface ozone (O3) pollution has become a prominent air quality problem in the Yangtze River Delta (YRD) region of China in recent years. Since O3 is non-linearly related to its precursors (volatile organic compounds (VOCs), nitrogen oxides (NOx)), identifying the characteristics of VOCs is significant for the control of O3 pollution. In this study, online observation of ambient VOCs from August to October 2018 was conducted at 2 sites in Changzhou, an industrial city located in the central YRD region, to investigate the O3 pollution characteristics, sources of VOCs, and their roles in O3 formation. The average concentration of VOCs in Changzhou during the observational period was 39.52 ± 23.14 ppb. Alkanes, oxygenated VOCs (OVOCs), and halocarbons were the main contributors to the total VOCs concentration, with the average relative contributions of 39.4%, 23.1%, and 16.1%, respectively. An observation-based model (OBM) was used to investigate the sensitivity of O3 formation to VOCs and NOx. Results of relative incremental reactivity (RIR) of individual VOC and empirical kinetics modeling approach (EKMA) showed that the O3 formation in Changzhou was within the VOCs-limited regime. Anthropogenic VOCs with the largest RIR values were xylenes and propene, respectively. The positive matrix factorization (PMF) model was applied to quantitatively identify the sources of VOCs. Six factors were resolved, including vehicle exhaust, gasoline evaporation, paint and solvent usage, electronic manufacturing, petrochemical industry, and biogenic source & secondary formation. The average relative contribution of traffic-related emissions to the total VOCs mass concentration was about 49.5%, followed by electronic manufacturing (22.9%), paint and solvent usage (14.7%), and petrochemical industry (7.1%). The average relative contributions of individual sources for xylenes and propene were further compared. Xylenes were mainly emitted from paint and solvent usage (60%), electronic manufacturing (17%), and vehicle exhaust (16%). Petrochemical industry (67%) and vehicle exhaust (30%) were the major sources of propene. Therefore, VOCs from industrial emissions and traffic-related emissions should be given priority for the control of O3 pollution in the central YRD region.