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

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 CH 2 OO with CH 3 O 2 and CH 3 C(O)O 2 . 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, N 2 ). A combined rate coefficient of k (CH 2 OO + RO 2, RO 2 = CH 3 O 2 /CH 3 C(O)O 2 ) = (2.4 ± 1.2) × 10 –11 cm 3 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.