Kinetics, product distribution and atmospheric implications of the gas-phase oxidation of allyl sulfides by OH radicals.

Relative rate coefficients of the OH radical -initiated oxidation of allyl methyl sulfide (AMS, H2CCHCH2SCH3) and allyl ethyl sulfide (AES, H2CCHCH2SCH2CH3) have been measured at atmospheric pressure of synthetic air and 298 K: kAMS= (4.98 ± 1.42) and kAES= (6.88 ± 1.49) × 10-11 cm3 molecule-1 s-1 by means of in situ FTIR spectroscopy. In addition, the molar yields of the main reaction products of AMS with OH radicals formed in the absence and presence of nitric oxides (NOX) were determined to be the following: sulfur dioxide (95 ± 12) % and (51 ± 12) % for acrolein (50 ± 9) % and (41 ± 9) %. In the reaction of AES with OH radicals, the following molar yields were obtained: for sulfur dioxide (88 ± 13) % and (56 ± 12) % for acrolein (36 ± 9) % and (41 ± 9) %. The present results suggest that the abstraction at C3 plays an important role in the oxidation mechanism as the addition to the double bond. This work represents the first study of the OH radical interaction with AMS and AES carried out under atmospheric conditions. The atmospheric implications were discussed in terms of the atmospheric residence times of the sulfur-containing compounds studied and the products formed in the presence and absence of NOx. SO2 formation seems to be the main fate of the gas-phase allyl sulfides oxidation with significant acidifying potentials and short-chain aldehydes production like formaldehyde and acetaldehyde.