Measurement report: High Contributions of Halohydrocarbon and Aromatic Compounds to Emissions and Chemistry of Atmospheric VOCs in Industrial Area

Abstract. Volatile organic compounds (VOCs) are key components for tropospheric chemistry and air quality. We investigated ambient VOCs in an industrial area in Nanjing, China from July 2018 to May 2020. The total VOCs (TVOCs) concentration was 59.8 ± 28.6 ppbv during the investigation period. About twice TVOCs concentrations were observed in autumn (83 ± 20 ppbv) and winter (77.5 ± 16.8 ppbv) seasons compared to those in spring (39.6 ± 13.1 ppbv) and summer (38.8 ± 10.2 ppbv). Unlike previous studies in Nanjing, oxygenated-VOCs (OVOCs) and halohydrocarbons were measured, the observed TVOCs was about 1.5 and 3-times higher than those previously reported in the same study area and a nonindustrial suburban area in Nanjing, respectively. Observed TVOCs concentrations were similar to those in metropolitan city Beijing and Shanghai, however, it was about 1.5–3 folds higher than those in Lanzhou, Wuhan, Tianjin, Ningbo, Chengdu, London, Los Angeles, and Tokyo. Due to the industrial influence, halohydrocarbons (14.3 ± 7.3 ppbv, 24 %) VOC-group was the second largest contributor to the TVOCs after alkanes (21 ± 7 ppbv, 35 %), which is in contrast with the previous studies in Nanjing and also in almost other regions in China. Relatively high proportions of helohydrocarbons and aromatics were observed in autumn (25.7 and 19.3 %, respectively) and winter (25.8 and 17.6 %, respectively) compared to those in summer (20.4 and 11.8 %, respectively) and spring (20.3 and 13.6 %, respectively). According to the potential source contribution function (PSCF), short-distance transports from the surrounding industrial areas and cities were the main reason for high VOC concentration in the study area. According to positive matrix factorization (PMF) model results, industry-related sources (23–47 %) followed by vehicle emissions (24–34 %) contributed the major portion to the ambient VOC concentrations. Whereas aromatics followed by alkenes were the top contributors to the loss rate of OH radicals (LOH) (37 and 32 %, respectively), alkenes followed by aromatics contributed most to the ozone formation potential (OFP) (39 and 28 %, respectively). Besides, the aromatics VOC-group was also the major contributor to the secondary organic aerosol potential (SOAP) (97 %). According to the empirical kinetic modelling approach (EKMA) and relative incremental reactivity (RIR) analysis in assistance with a photochemical box model, the study area was in the VOC-sensitive regime for ozone (O3) formation during all the measurements seasons. Therefore, mainly alkenes and aromatics emissions chiefly from industries and automobiles should be reduced to decrease the secondary air pollution formation in the study area.