New formation and fate of Isoprene SOA markers revealed by field data-constrained modeling

Abstract Particulate 2-methyltetrols (2-MT) and 2-methylglyceric acid (2-MG) are typically used to indicate the abundance of isoprene-derived secondary organic aerosols (SOA). However, their formation fate not fully understood. In this study, we showed that particulate 2-MT 2-MG collected at multiple monitoring sites under a wide range atmospheric emission conditions, with concentrations spanning six orders magnitudes, well reproduced an expanded isoprene-SOA scheme implemented into Community Multiscale Air Quality (CMAQ) model. The considers three-phase (gas-aqueous-organic phase) partitioning, from acid-driven multiphase reactions, degradation by OH radicals in gas aqueous phases. model results reveal non-aqueous pathway or direct biogenic is needed supplement commonly assumed reaction process explain observed concentrations. This missing contributes 20–40% areas aerosol pH<2 more than 70% less acidic conditions (pH~2–5), such as those encountered western US China. typical summertime gas-phase photochemical lifetimes estimated be 4–6 20–30 h, respectively, approximately 20–40 h. Our simulations show predicted mainly influenced its phase loss OH, but sensitive due preferential partitioning two tracers phases, respectively.