Contributions of different anthropogenic volatile organic compound sources to ozone formation at a receptor site in the Pearl River Delta region and its policy implications
Abstract. Volatile organic compounds (VOCs) are key precursors of photochemical smog. Quantitatively evaluating the contributions of VOCs sources to ozone (O3) formation could provide valuable information for emissions control and photochemical pollution abatement. This study analysed the continuously measured VOCs during the photochemical season in 2014 at a receptor site (Heshan site, HS) in the Pearl River Delta (PRD) region, where photochemical pollution has been a long-standing issue. The averaged mixing ratio of measure VOCs was 34 ± 3 ppbv, with the largest contribution from alkanes (17 ± 2 ppbv, 49 %), followed by aromatics, alkenes, and acetylene. The positive matrix factorization (PMF) model was applied to resolve the anthropogenic sources of VOCs, coupled with a photochemical-aged-based parameterization that better considers the photochemical processing effects. Four anthropogenic emission sources were identified and quantified, with gasoline vehicular emission as the most significant contributor to the observed VOCs, followed by diesel vehicular emissions, biomass burning, and solvent usage. The O3 photochemical formation regime at HS was identified as VOCs-limited by a photochemical box model with the master chemical mechanism (PBM-MCM). The PBM-MCM model results also suggested that vehicular emission was the most important source to the O3 formation, followed by biomass burning and solvent usage. Sensitivity analysis indicated that in order to prevent the increment of O3 concentration, the abatement ratios of the individual VOC source vs. NOx should be higher than 3.8, 4.6, 4.6, and 3.3, respectively, for diesel vehicular emission, solvent usage, biomass burning, and gasoline vehicular emission, respectively. Based on the above results, a brief review on the policies on the controlling of vehicular emissions and biomass burning in the PRD region from a regional perspective were also provided in this study. It reveals that different policies have been/being implemented and formulated could help to alleviate the photochemical pollution in the PRD. Nevertheless, evaluation on the cost-benefit of each policy is still needed to improve the air quality.