Nonlinear Formation of Secondary Organic Aerosol from Biogenic VOC Mixtures

Secondary organic aerosol (SOA) plays a significant role in air quality, climate, and human health. SOA produced from the oxidation of biogenic volatile organic compounds (VOCs) in the presence of reactive nitrogen species constitutes a major fraction of ambient organic aerosol. This study investigates the nonlinear effects of mixed biogenic VOC systems, including monoterpenes and sesquiterpenes, on the yield, chemical composition, and volatility of SOA. Smog chamber experiments show that SOA yields for mixtures are reduced compared to single-component systems, likely due to interactions among C10 and C15 RO₂ radicals. High-resolution mass spectrometry identifies unique chemical species specific to the mixed-component system, while volatility analysis reveals that sesquiterpene-derived compounds and monoterpene-sesquiterpene cross-reaction products dominate. Model simulations using the Master Chemical Mechanism reveal substantial discrepancies between predicted and experimentally observed SOA yields and volatility. These findings highlight the complexity of SOA formation from VOC mixtures, emphasizing the need to incorporate nonlinear precursor interactions into atmospheric chemistry and air quality models.