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) plays an important role for removal of Criegee intermediates as well as in oxidation of atmospheric HNO because of its fast reaction rate. Theoretical prediction suggests that the product branching ratios of the reaction of the simplest Criegee intermediate CHOO with HNO are strongly pressure dependent and the CHOO may be catalytically converted to OH and HCO radicals by HNO. The direct quantification of HO 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 CHOO + HNO are investigated. A pressure independent rate coefficient of (1.9 ± 0.2) × 10 cm molecule s 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 CHOO, formaldehyde (CHO), OH and HO radicals. At the total pressure of 12.5 Torr, the yield for the formation of NO + CHO + HO is 36% and only 3.2% for OH + CH(O)NO, whereas the main remainder may be thermalized nitrooxymethyl hydroperoxide (NMHP, NOCHOOH). Additionally, the fractional yields of both the OH and HO product channels are decreased by a factor of roughly 2 from 12 to 60 Torr, indicating that there is almost no catalytic conversion of CHOO to the OH radicals in the presence of HNO.