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

[摘要] Recent studies indicate that isoprene and its gas-phase oxidation products could contribute aconsiderable amount of aerosol through aqueous-phase acid-catalyzedoxidation with hydrogen peroxide (H₂O₂), although thesource of H₂O₂ is unclear. The present study revealed apotentially important route to the formation of aqueous oxidants,including H₂O₂, from the aqueous-phase ozonolysis ofmethacrolein (MAC) and methyl vinyl ketone (MVK). Laboratorysimulation was used to perform the atmospheric aqueous-phaseozonolysis at different pHs and temperatures. Unexpectedly highmolar yields of the products, including hydroxylmethyl hydroperoxide(HMHP), formaldehyde (HCHO) and methylglyoxal (MG), of both of thesereaction systems have been seen. Moreover, these yields are almostindependent of pH and temperature and are as follows: (i) forMAC–O₃, 70.3±6.3% HMHP, 32.3±5.8% HCHO and98.6±5.4% MG; and (ii) for MVK–O₃, 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–O₃. HMHP isunstable in the aqueous phase and can transform into H₂O₂and HCHO with a yield of 100%. We suggest that the aqueous-phaseozonolysis of MAC and MVK can contribute a considerable amount ofoxidants in a direct and indirect mode to the aqueous phase and thatthese 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 theaqueous-phase acid-catalyzed reaction of H₂O₂ with MAC,even if there are no other sources of oxidants.

[学科分类] 大气科学