Aqueous-phase ozonolysis of methacrolein and methyl vinyl ketone: a potentially important source of atmospheric aqueous oxidants

• Main Authors: Z. M. Chen, H. L. Wang, L. H. Zhu, C. X. Wang, C. Y. Jie, W. Hua
• Format: Article
• Language: English
• Published: Copernicus Publications 2008-04-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/8/2255/2008/acp-8-2255-2008.pdf

Recent studies indicate that isoprene and its gas-phase oxidation products could contribute a considerable amount of aerosol through aqueous-phase acid-catalyzed oxidation with hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), although the source of H<sub>2</sub>O<sub>2</sub> is unclear. The present study revealed a potentially important route to the formation of aqueous oxidants, including H<sub>2</sub>O<sub>2</sub>, from the aqueous-phase ozonolysis of methacrolein (MAC) and methyl vinyl ketone (MVK). Laboratory simulation was used to perform the atmospheric aqueous-phase ozonolysis at different pHs and temperatures. Unexpectedly high molar yields of the products, including hydroxylmethyl hydroperoxide (HMHP), formaldehyde (HCHO) and methylglyoxal (MG), of both of these reaction systems have been seen. Moreover, these yields are almost independent of pH and temperature and are as follows: (i) for MAC–O<sub>3</sub>, 70.3±6.3% HMHP, 32.3±5.8% HCHO and 98.6±5.4% MG; and (ii) for MVK–O<sub>3</sub>, 68.9±9.7% HMHP, 13.3±5.8% HCHO and 75.4±7.9% MG. A yield of 24.2±3.6% pyruvic acid has been detected for MVK–O<sub>3</sub>. HMHP is unstable in the aqueous phase and can transform into H<sub>2</sub>O<sub>2</sub> and HCHO with a yield of 100%. We suggest that the aqueous-phase ozonolysis of MAC and MVK can contribute a considerable amount of oxidants in a direct and indirect mode to the aqueous phase and that these compounds might be the main source of aqueous-phase oxidants. The formation of oxidants in the aqueous-phase ozonolysis of MAC and MVK can lead to substantial aerosol formation from the aqueous-phase acid-catalyzed reaction of H<sub>2</sub>O<sub>2</sub> with MAC, even if there are no other sources of oxidants.