Persistence of Monoterpene-Derived Organic Peroxides in the Atmospheric Aqueous Phase

Abstract

Organic peroxides are essential reactive species formed during the atmospheric oxidation of organic compounds and can effectively partition into aqueous aerosols and cloud droplets, yet their aqueous-phase fate in aerosol and cloud water remains poorly characterized. Here, we report the first investigation of the isomer-resolved aqueous-phase chemical behaviors of a large suite of organic peroxides in dissolved monoterpene secondary organic aerosol (SOA). We find that about half of individual peroxides undergo noticeable hydrolysis, while the other half mainly react via nonhydrolysis unimolecular or bimolecular pathways. The chemical complexity of organic peroxides, as well as the effects of coexisting organic compounds in dissolved SOA, results in diverse chemical behaviors of individual peroxides and a complicated dependence on the water content, pH, and even organic concentration in the aqueous phase. Compared to the previously investigated α-substituted hydroperoxides that undergo hydrolysis on timescales of minutes to a few hours, the vast majority of organic peroxides studied herein are significantly more persistent in the aqueous phase, with decay rate constants of 1.8 × 10–6 to 2.4 × 10–4 s–1 and the corresponding e-folding lifetimes of 1.1–153 h under atmospherically relevant conditions, which would have distinctly different impacts on atmospheric chemistry and human health.