Characteristics, source apportionment, and secondary transformation of volatile organic compounds during different seasons at an urban site in southeast China.

Volatile organic compounds (VOCs) are key precursors to secondary organic aerosol (SOA) and ozone (O3) formation. In this study, 114 VOCs were continuously online measured in Wuxi, from March 2022 to February 2023. Annual data revealed clear seasonal variation in VOCs concentrations, the lowest in autumn (29.78 ± 12.21 ppbv) and the highest in winter (37.63 ± 15.85 ppbv). Alkanes (36.40 %) and oxygenated VOCs (OVOCs, 32.94 %) dominated annually. Diurnal variation in VOCs species (e.g., alkanes, alkenes, aromatics, and halohydrocarbons) was similar to total VOCs (TVOCs) and presented bimodal patterns. OVOCs contributed the most to ozone formation potential (OFP, 42.2 %-51.7 %) and OH loss rate (LOH, 43.97 %-51.14 %). Aromatics accounted for 95.9 %-96.9 % of SOA formation potential (SOAFP), with toluene, m/p-xylene, and benzene being the dominant species. Positive matrix factorization (PMF) revealed vehicular exhaust (20 %) and fuel combustion (28 %) were the major VOCs sources. Seasonally, fuel combustion contributions peaked in winter (35 %) due to heating activities, while biogenic emissions (10 %) were prominent in summer. Potential source contribution function (PSCF) results emphasized winter VOCs mainly from local emissions (short-distance transport within the province, 40.49 %), contrasting with minor regional contributions (< 15 %). From empirical kinetics modelling approach (EKMA), the O3 formation is more dominated by VOCs control while it featured the transitional regime in the summer. According to the relative incremental reactivity (RIR), limiting anthropogenic VOCs emissions was an effective way to mitigate O3 pollution, while blindly reducing NOx may aggravate O3 pollution. The results provide an important scientific basis for Wuxi to formulate corresponding O3 pollution control strategies.