Characteristics, source apportionment and contribution of VOCs to ozone formation in Wuhan, Central China

Abstract

Based on the detailed data of volatile organic compounds (VOCs) with 102 components measured continuously from September 2016 to August 2017 in Wuhan, the pollution characteristics, source apportionment, chemical reactivity and contribution to O3 formation were analysed. The results revealed that the annual average concentration of total VOCs (TVOCs) was 34.65 ppbv. Alkanes were the species with the largest concentration, which accounted for 45.88% of TVOCs, and propane, ethane and ethene were the most abundant components. Diagnostic ratios (toluene/benzene, typical VOC species/acetylene) showed that vehicle exhaust emissions had significant effects on VOCs. Eight major sources were identified by positive matrix factorization (PMF), which included vehicular exhaust (24.42%), industrial sources (16.43%), coal burning (14.18%), solvent usage in painting/coating (13.48%), liquefied petroleum gas (LPG) usage (12.57%), fuel evaporation (11.34%), biomass burning (5.11%) and biogenic sources (2.47%). In addition, industrial sources, vehicle exhaust and LPG usage were the main sources that significantly aggravated VOC pollution in Wuhan. Potential source contribution function (PSCF) results showed that local pollution sources were the main sources influencing VOC pollution in Wuhan. The results of Empirical Kinetic Modelling Approach (EKMA) showed that Wuhan belongs to a VOC limited area. Finally, the results of the OH radical loss rate (LOH) and ozone formation potential (OFP) showed that alkenes were the species with the largest amount of chemical activity, in which the highest OH radical loss rate was 42.56%. Simultaneously, alkenes contributed the most to O3 formation, which accounted for 48.34%. The results can provide references for local governments regarding control strategies of VOCs and O3 pollution.