The atmospheric chemistry of acetone and alpha- and beta-pinene

alpha- and beta-Pinene are the most abundant monoterpenes emitted to the atmosphere, and account for 10% of all biogenic volatile organic compounds emitted annually. Because of their high reactivies with the OH radical, these compounds have the potential to contribute to ozone and secondary aerosol formation in the atmosphere. Acetone, one of the products of alpha- and beta-pinene oxidation, can also contribute to OH production in the upper troposphere. As a result, the chemical mechanisms of the oxidation of alpha-pinene, beta-pinene and acetone in the atmosphere are of considerable interest to atmospheric chemists. The kinetics and mechanisms of these compounds were studied using the discharge flow technique.; The rate constant for the OH + acetone reaction was independent of pressure between 2 and 5 Torr and between 270 and 400K. The measured rate constant was (1.73 +/- 0.06) x 10-13 cm3 molecule-1 s-1 at 300K and increased, following Arrhenius behavior, with temperature above 300K. However non-Arrhenius behavior was observed at temperatures below 300K. The OH + acetone-d 6 reaction showed similar behavior and a significant primary kinetic isotope effect was observed. These results suggest that H-abstraction is the predominant mechanism for the OH-initiated oxidation of acetone, consistent with recent measurements.; The kinetics of the beta-pinene reaction was studied between 300 and 435K at 5 Torr total pressure. The measured bimolecular rate constant was (7.72 +/- 0.44) x 10-11 cm3 molecule-1 s-1 at 300K, and exhibited a negative temperature dependence suggesting a mechanism involving OH-addition. The temperature dependence was larger than that observed at 50 and 760 Torr.; With the OH-initiated oxidation of alpha-pinene and beta-pinene in the presence of O2 and NO, regeneration of the OH radical was observed. The measured OH radical concentration profiles in the presence of NO were compared to simulations based on the Master Chemical Mechanism and the Regional Atmospheric Chemistry Mechanism oxidation models for alpha- and beta-pinene in order to determine the mechanism that best describes the observed radical propagation. These models provide a good prediction of the OH cycling by alpha-pinene and beta-pinene, and suggest that these models provide a reasonable representation of the efficiency of ozone production in the atmosphere.