[Characteristics，Sources，and Ozone-sensitive Species of VOCs in Four Seasons in Yuncheng]

Based on the one-year observational data of volatile organic compounds （VOCs） in an urban area of Yuncheng in 2021， the concentration， composition， sources， and ozone-sensitive species of VOCs in four seasons were analyzed. The results showed that the average annual concentration of VOCs was （32.1 ±24.2）×10^-9， i.e.， at the national middle level. The seasonal concentrations of VOCs were in the order of： winter （46.3×10^-9）> autumn （35.5×10^-9）> spring （25.6×10^-9）> summer （21.2×10^-9）. Alkanes and OVOCs were the most dominant VOCs compounds， accounting for 69.0%-80.4% of TVOCs in Yuncheng. Affected by changes in source emissions， the proportion of OVOCs was higher in spring and summer （41%-43%）， whereas the proportion of alkanes was higher in autumn and winter （42%-43%）. Vehicle exhaust， LPG/NG， industrial production， and combustion sources were identified as the main sources of VOCs in Yuncheng. The largest contributors in the four seasons were vehicle exhaust （28.5% in spring）， secondary + combustion sources （29.0% in summer）， LPG/NG sources （30.4% in autumn）， and coal combustion （27.3% in winter）. The ozone formation was located in the transitional regime in summer and in the VOC-limited regime in other seasons. Ozone production was more sensitive to alkenes （isoprene， ethylene， and propene）， OVOCs （acetaldehyde and propanal）， and aromatics （xylene， toluene， and benzene）. Winter was more sensitive to ethylene， and the other seasons were more sensitive to isoprene. The primary emission sources related to these sensitive species should be reduced to achieve the goal of air quality improvement.