Kinetics and pressure-dependent HO x yields of the reaction between the Criegee intermediate CH 2 OO and HNO 3 .

The reaction of Criegee intermediates with nitric acid (HNO 3 ) plays an important role for removal of Criegee intermediates as well as in oxidation of atmospheric HNO 3 because of its fast reaction rate. Theoretical prediction suggests that the product branching ratios of the reaction of the simplest Criegee intermediate CH 2 OO with HNO 3 are strongly pressure dependent and the CH 2 OO may be catalytically converted to OH and HCO radicals by HNO 3 . The direct quantification of HO x radicals formed from this reaction is hence crucial to evaluate its atmospheric implications. By employing mid-infrared multifunctional dual-comb spectrometers, the kinetics and product yields of the reaction CH 2 OO + HNO 3 are investigated. A pressure independent rate coefficient of (1.9 ± 0.2) × 10 -10 cm 3 molecule -1 s -1 is obtained under a total pressure of 6.3-58.6 Torr at 296 K. The product branching ratios are derived by simultaneous determination of CH 2 OO, formaldehyde (CH 2 O), OH and HO 2 radicals. At the total pressure of 12.5 Torr, the yield for the formation of NO 2 + CH 2 O + HO 2 is 36% and only 3.2% for OH + CH 2 (O)NO 3 , whereas the main remainder may be thermalized nitrooxymethyl hydroperoxide (NMHP, NO 3 CH 2 OOH). Additionally, the fractional yields of both the OH and HO 2 product channels are decreased by a factor of roughly 2 from 12 to 60 Torr, indicating that there is almost no catalytic conversion of CH 2 OO to the OH radicals in the presence of HNO 3 .