PNNL

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 and fate are not fully understood. In this study, we showed that particulate 2-MT and 2-MG collected at multiple monitoring sites in the United States (US) and China and in the Asian continental outflow regions in the West Pacific can be well reproduced with an expanded isoprene-SOA scheme implemented into the Community Multiscale Air Quality (CMAQ) model. The scheme considers their three-phase (gas-aqueous-organic phase) partitioning, formation from acid-driven multiphase reactions, and degradation by OH radicals in the gas and aqueous phases. Our results suggest that including a previously unconsidered gas-phase 2-MT formation from isoprene under low-NOx conditions or direct biogenic emissions rectifies the under-prediction biases at the monitoring sites. This missing pathway can contribute to 20-40% of 2-MT in areas with aerosol pH