NOx-driven chemical transformation of terpene mixtures: Linking highly oxygenated organic molecules to health effects in secondary organic aerosol.

Biogenic volatile organic compounds (BVOCs), particularly terpenes, represent the dominant global source of secondary organic aerosols (SOA). However, the crucial investigation in terpene mixture under various nitrogen oxides (NOx) conditions needs to be further explored. To comprehensively understand the mixed SOA composition and its associated health effects, we simulated the mixed oxidation of α-pinene and isoprene in a smog chamber under various NOx conditions to investigate SOA formation and its related health effects. We found that increasing NOx levels led to the formation of CHON compounds, suppressing functionalized products and oligomers. Results of the oxidative potential and total peroxides of SOA showed that mixed SOA had combined redox characteristics (isoprene SOA > mixed SOA > α-pinene SOA). The oxidative potential of isoprene SOA decreased as NOx increased, while α-pinene SOA was slightly affected. Results from iodometry combined with mass spectrometry indicated that hydrogen peroxides (ROOH) in highly oxygenated molecules played a crucial role in SOA health effects. NOx was found to influence the production of ROOH by interfering with the RO2 + HO2 and RO2 isomerization pathways. These results indicate that the reactive intermediate components in BVOC mixture under various NOx conditions are important factors influencing health effects of aerosol.