Fenton-like reactions of methylhydroperoxide and ethylhydroperoxide with Fe2+ in liquid aerosols under tropospheric conditions

Laboratory experiments were performed to study the "Fenton-like" reduction of methylhydroperoxide and ethylhydroperoxide by Fe2+ ions in aqueous solutions, under tropospheric conditions. The rate constants obtained at 6degreesC and pH = 2 (16+/-5 and 24+/-9 M-1 s(-1), respectively) are of the same order as the rate constant of H2O2 reduction by Fe2+. The major reaction products identified were the corresponding aldehydes (formaldehyde and acetaldehyde). The other identified organic products (the corresponding acids and hydroxy hydroperoxides) accounted for < 10% of the total organic reaction products. Aldehydes and organic acids total production represented > 87% of the consumed hydroperoxides. Between the two possible mechanisms (i.e. Fe2+ + ROOH --> Fe3+ + OH + RO. (M1) and Fe2+ + ROOH --> Fe3+ + (OH)-O-. + RO- (M2)), the experiments showed that M2 is negligible. The alkoxy (RO.) radicals formed in (M1) further rearrange in water solution, and react with oxygen to form peroxy radicals which decompose, leading to the formation of aldehydes. This decomposition is in competition with (i) the self-reaction forming the corresponding acids and H2O2, and (ii) the reaction with HO2 radicals forming the corresponding hydroxy hydroperoxides. The atmospheric implications of these reactions are discussed. (C) 2003 Elsevier Ltd. All rights reserved.