To investigate the seasonal variations in the concentrations of atmospheric volatile organic compounds (VOCs) in the urban area of Chengdu, VOC species were monitored from December 2018 to November 2019, and the concentrations, chemical composition, chemical reactivity, and sources of VOCs were analyzed. Average volume fraction of VOCs in spring, summer, autumn, and winter are 32.29×10-9, 36.25×10-9, 40.92×10-9, and 49.48×10-9, respectively. The concentrations in winter are significantly higher than the winter concentrations measured in other areas. There is no significant difference between VOC concentrations in spring and summer, but component concentrations vary from season to season. In winter, alkanes account for the largest proportion of total VOCs owing to vehicle emissions. The proportion of oxygen (nitrogen)-containing volatile organic compounds in summer and autumn is much higher than that in spring and winter. Volatile emissions from primary sources and secondary conversions have a great contribution. The average concentration of key components of VOCs in different seasons did not change significantly. C2-C4 alkanes, ethylene, acetylene, and dichloromethane concentrations may be significantly affected by vehicle exhaust, oil and gas volatilization, solvent use, and LPG fuel use. ·OH consumption rate and OFP calculations show that key active species are mainly m/p-xylene, ethylene, propylene, 1-hexene, toluene, isopentane, and n-butane. Therefore, these species should be given priority in emissions control measures. Since the temperature in spring and summer is higher than in autumn and winter, and the UV rays are more intense, PMF analysis reveals the natural sources and the secondary emission sources as the major sources. The oil and gas volatilization source contributes to 9% of VOC concentrations in summer. The major VOC sources in autumn and winter are vehicle exhaust and combustion sources. Emissions from the combustion sources contribute to 25% and emissions from the catering sources in autumn and winter contribute to 9% of total VOC levels.
Keywords: Chengdu; chemical reactivity; seasonal characteristics; source apportionment; volatile organic compounds (VOCs).