Explicit modelling of seasonal isoprene chemical processing in Wuhan: formation of ozone and formaldehyde

Ozone(O₃) pollution has become an increasing air quality issue in China, with frequent high O₃ episodes in Wuhan, central China. Isoprene, a highly reactive volatile organic compound, plays an important role in urban O₃ formation. In this study, simultaneous measurements of volatile organic compounds (VOCs), O₃, and meteorological parameters were conducted at an urban site in Wuhan during June 2023 and February 2024. The concentration of isoprene in winter (0.025 ± 0.003 ppbv) was found to be significantly lower when compared to those in summer (0.31 ± 0.02 ppbv). Source apportionment by Positive Matrix Factorization (PMF) revealed biogenic emissions as the dominant source of isoprene (89% in summer, 63% in winter), followed by vehicle exhaust (6% summer, 19% winter) and solvent/VCP-dominated usage (3% summer, 17% winter). Model simulation results showed that reductions in both biogenic and anthropogenic isoprene emissions led to decreased radical concentration and suppressed daytime O₃ production, with stronger responses observed in summer. The simulated daily mean O₃ concentrations dropped by 3% under biogenic isoprene reduction and 0.7% under anthropogenic isoprene reduction. Correspondingly, the average net daytime production rate of O₃ decreased by 0.59 ppbv h⁻¹ and 0.13 ppbv h⁻¹, respectively. In addition, the daily average formaldehyde (HCHO) declined by 0.05 ppbv (∼20%) and 0.01 ppbv (∼5%). This study reveals the substantial impact of anthropogenic/biogenic isoprene chemistry on urban air quality and advances understanding of radical-driven mechanisms governing secondary pollutant (O₃, HCHO) formation in central China.