2025/03/06 by Jiayun Zhao, Sahir Gagan, Molly Frauenheim +7 · 1 voice
Earth and Planetary Sciences · Environmental Science · Materials Science · #Air Quality Monitoring and Forecasting #Atmospheric chemistry and aerosols #Catalytic Processes in Materials Science
paper · doi:10.1021/acsestair.4c00367
openalex publication_date 2025/03/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/14
Isoprene, the most abundant nonmethane volatile organic compound in the atmosphere, undergoes photochemical reactions with hydroxyl radical ( • OH), a major sink for isoprene, leading to the formation of secondary organic aerosol (SOA). Using a Vocus Chemical Ionization Mass Spectrometer with ammonium-adduct ions (Vocus NH 4 + CIMS), this study used the positive ion mode to quantify the yields and time-dependent reactive uptake of oxidized volatile organic compounds (OVOCs) produced from • OH-initiated oxidation of isoprene under dry conditions. Molar gas-phase yields of key oxidation products were constrained using sensitivities derived from a voltage scan of the front and back end of the Vocus ion–molecule reactor region. Carefully designed chamber experiments measured uptake coefficients ( γ ) for key isoprene-derived oxidation products onto acidic sulfate particles. The γ values for both C 5 H 10 O 3 isomers (IEPOX/ISOPOOH) and C 5 H 8 O 4, another epoxy species from isoprene photo-oxidation, rapidly decreased as the SOA coating thickness increased, demonstrating a self-limiting effect. Despite ISOPOOH/IEPOX contributing around 80% to total reactive uptake, other oxidation products from isoprene photooxidation were estimated to contribute 20% of the total SOA formation. These findings highlight the importance for future models to consider the self-limiting effects of ISOPOOH/IEPOX and SOA formation through non-IEPOX pathways.