Impact of Criegee Intermediate Reactions with Peroxy Radicals on Tropospheric Organic Aerosol

Abstract

Peroxy radicals and carbonyl oxides (Criegee intermediates) are produced in the troposphere during OH and ozone-initiated oxidation of hydrocarbons. Reactions between these species have previously been shown to form highly oxidized molecules which can condense to form secondary organic aerosols. Here, cavity ring-down spectroscopy coupled with laser flash photolysis was used to measure directly rate coefficients for reactions of CH2OO with CH3O2 and CH3C(O)O2. The rate coefficients were found to be similar within the measurement uncertainties and only weakly dependent on temperature (in the range 243–310 K) and pressure (20–100 Torr, N2). A combined rate coefficient of k (CH2OO + RO2, RO2 = CH3O2/CH3C(O)O2) = (2.4 ± 1.2) × 10–11 cm3 molecule–1 s–1 was obtained under these conditions. Global modeling using STOCHEM-CRI, updated with monoterpene chemistry generating Criegee intermediates and supplemented by regional box modeling, shows that this class of Criegee intermediate + peroxy radical reactions can contribute up to ∼1.3% of secondary organic aerosol production in forested regions of the world.