Kinetics and atmospheric implications of peroxy radical cross reactions involving the CH₃C(O)O₂ radical

The kinetics of the reactions of selected secondary and tertiary peroxy radicals (RO 2 ) with CH 3 C(O)O 2 have been investigated. Values of (1.0±0.3)×10 −11 , (1.1±0.3)× −11 (1.0±0.5)×10 −11 and (1.1±0.3)×10 −11 (units of cm 3 molecule −1 s −1 , statistical errors 2σ) have been obtained at 298 K for the rate constants of the reactions of CH 3 C(O)O 2 radicals with c ‐C 6 H 11 O 2 , sec‐C 10 H 21 O 2 , sec‐C 12 H 25 O 2 and t ‐C 4 H 9 O 2 radicals, respectively. A systematic propagation of error analysis has yielded overall (statistical + systematical) uncertainty factors of 1.6, 1.8, 1.9, and 1.5, respectively, for the above rate constant values. The present results, combined with the results previously reported for primary peroxy radicals, show that all cross reactions of CH 3 C(O)O 2 are fast with rate constants of around 1.0×10 −11 cm 3 molecule −1 s −1 , independent of the RO 2 radical structure and of its self‐reaction rate constant. This suggests that all acylperoxy radicals present the same high reactivity as CH 3 C(O)O 2 , and hence it is proposed to assign the above rate constant value to all cross reactions of acylperoxy radicals. These new rate constant values were implemented in the Regional Atmospheric Chemistry Mechanism [ Stockwell et al ., 1997] to estimate the importance of the cross reactions in the chemistry of acylperoxy radicals in the troposphere. In the case of a moderately polluted troposphere, under low NO x and high volatile organic compounds (VOC) concentrations, the cross reactions of acylperoxy radicals with organic peroxy radicals account for more than 20% of the acylperoxy loss reactions, and peroxyacyl nitrates concentrations decrease by more than 4%, compared with the previous estimates of Kirchner and Stockwell [1996].