Laboratory evidence of organic peroxide and peroxyhemiacetal formation in the aqueous phase and implications for aqueous OH

摘要

Aqueous chemistry in atmospheric waters (e.g., cloud droplets or wetaerosols) is considered a potentially important atmospheric pathway toproduce secondary organic aerosol (SOA). Water-soluble organiccompounds with small carbon numbers (C–C) are precursors forSOA; products include organic acids, organic sulfates, andhigh-molecular-weight compounds/oligomers. Fenton reactions and the uptake ofgas-phase OH radicals are considered to be the major oxidant sources foraqueous organic chemistry. However, the sources and availability of oxidantsin atmospheric waters are not well understood. The degree to which OH isproduced in the aqueous phase affects the balance of radical and non-radicalaqueous chemistry, the properties of the resulting aerosol, and likely itsatmospheric behavior.This paper demonstrates organic peroxide formation during aqueousphotooxidation of methylglyoxal using ultra-high-resolution Fouriertransform ion cyclotron resonance electrospray ionization mass spectrometry(FTICR-MS). Organic peroxides are known to form through oxidation ofvolatile organic compounds. They contribute secondary organic aerosol (SOA)formation directly by forming peroxyhemiacetals and epoxides (i.e., IEPOX),and indirectly by enhancing gas-phase oxidation through OH recycling. Weprovide simulation results of organic peroxide/peroxyhemiacetal formation inclouds and wet aerosols and discuss organic peroxides as a source ofcondensed-phase OH radicals and as a contributor to aqueous SOA.