J Environ Sci (China). 2026 May;163:48-58. doi: 10.1016/j.jes.2025.10.051. Epub 2025 Oct 30.
ABSTRACT
Volatile organic compounds (VOCs) regulate secondary pollutant formation by controlling both atmospheric oxidation capacity (AOC) intensity and ROx cycling efficiency. However, their dynamic mechanisms under varying seasonal and pollution conditions remain poorly understood. In this study, the seasonal variations in AOC and radical chemistry under contrasting pollution scenarios were quantified based on the synchronized measurements of VOCs and other trace gases in Jinan, China. Severe ozone pollution was identified in summer with 8 h average ozone (O3) levels exceeding the Chinese national ambient air quality on 22 days (or 73.3 % in frequency). Winter haze episodes (38.7 % in frequency) exhibited significant PM2.5 accumulation alongside pronounced VOCs enhancement. VOCs exhibited marked seasonal divergence: summer pollution depleted alkanes (-23 %) but enriched oxygenated VOCs (OVOCs, +28 %) through photochemical processing, whereas winter conditions amplified primary VOCs emissions. AOC confirmed summer dominance, with an average value of 1.6 × 107 molecules/(cm3·s), exceeding winter AOC values by 7-8 folds. OH reactivity analysis further distinguished seasonal drivers, with OVOCs accounting for 34 % of summer OH depletion versus NO2/CO-dominated consumption (61.2 %) in winter. HCHO/OVOCs photolysis contributed 65 %-89 % to HO2/RO2 production in summer (54 %-56 % in winter), whilst OH generation primarily originated from HONO photolysis (38 %-44 % in winter) and O3 dissociation (59 %-74 % in summer). Summer pollution episodes intensified radical cycling, as evidenced via accelerated summer OH production rates during pollution days.
PMID:41887866 | DOI:10.1016/j.jes.2025.10.051
