A product yield study of the reaction of HO2 radicals with ethyl peroxy (C2H5O2), acetyl peroxy (CH3C(O)O2), and acetonyl peroxy (CH3C(O)CH2O2) radicals

Abstract

The reaction between HO2 and RO2 radicals represents an importantchemical sink for HOx radicals in the atmosphere. On the basis ofa few product yield studies, these reactions are believed to formhydroperoxides almost exclusively (R8a), although several differentreaction channels may be thermodynamically accessible (R8a-d): RO2+ HO2 --> ROOH + O2 (R8a); RO2 + HO2 --> ROH + O-3 (R8b); RO2 + HO2--> RO + OH + O-2 (R8c); and RO2 + HO2 --> R'CHO + H2O + O-2 (R8d).Branching ratios for reaction R8 were measured for three organicperoxy radicals: ethyl peroxy (C2H5O2), acetyl peroxy (CH3C(O)O-2),and acetonyl peroxy (CH3C(O)CH2O2) radicals. Product yields weremeasured using a combination of long-path Fourier transform infraredspectroscopy and high-performance liquid chromatography with fluorescencedetection. Measured branching ratios for the reaction of the threeorganic peroxy radicals with HO2 are as follows: ethyl peroxy, Y8a-ETH> 0.93 +/- 0.10, Y8b-ETH = Y8c-ETH Y8d-ETH = 0; acetyl peroxy, Y8a-ACT= 0.40 +/- 0.16, Y8b-ACT = 0.20 +/- 0.08, Y8c-ACT = 0.40 +/- 0.16,and Y8d-ACT = 0; acetonyl peroxy, Y8a-ACN = 0.33 +/- 0.10, Y8b-ACN= Y8d-ACN = 0, and Y8c-ACN = 0.67 +/- 0.20. The atmospheric implicationsof these branching ratios are discussed.