Ambient volatile organic compounds at a receptor site in the Pearl River Delta region: Variations, source apportionment and effects on ozone formation

We present the continuously measurements of volatile organic compounds (VOCs) at a re-ceptor site (Wan Qing Sha,WQS) in the Pearl River Delta (PRD) region from September to November of 2017.The average mixing ratios of total VOCs (TVOCs) was 36.34± 27.9 ppbv with the dominant contribution from alkanes (55.5％),followed by aromatics (33.3％).The diurnal variation of TVOCs showed a strong photochemical consumption during daytime,resulting in the formation of ozone (O3).Five VOC sources were resolved by the positive ma-trix factorization (PMF) model,including solvent usage (28.6％),liquid petroleum gas (LPG)usage (24.4％),vehicle exhaust (21.0％),industrial emissions (13.2％) and gasoline evapora-tion (12.9％).The regional transport air masses from the upwind cities of south China can result in the elevated concentrations of TVOCs.Low ratios of TVOCs/NOx (1.534-0.88) sug-gested that the Os formation regime at WQS site was VOC-limited,which also confirmed by a photochemical box model with the master chemical mechanism (PBM-MCM).Further-more,the observation on high-Os episode days revealed that frequent O3 outbreaks at WQS were mainly caused by the regional transport of anthropogenic VOCs especially for aromat-ics and the subsequent photochemical reactions.This study provides valuable information for policymakers to propose the effective control strategies on photochemical pollution in a regional perspective.