The production of formaldehyde and hydroxyacetone in methacrolein photooxidation: New insights into mechanism and effects of water vapor. Journal of Environmental Sciences [Internet]. 2018;66:1-11. 访问链接Abstract.
Methacrolein (MACR) is an abundant multifunctional carbonyl compound with highreactivity in the atmosphere. In this study, we investigated the hydroxyl radical initiatedoxidation of MACR at various NO/MACR ratios (0 to 4.04) and relative humidities (< 3% to80%) using a flow tube. Meanwhile, a box model based on the Master Chemical Mechanismwas performed to test our current understanding of the mechanism. In contrast to thereasonable predictions for hydroxyacetone production, the modeled yields of formaldehyde(HCHO) were twice higher than the experimental results. The discrepancy was ascribed tothe existence of unconsidered non-HCHO forming channels in the chemistry of CH3C(=CH2)OO., which account for approx. 50%. In addition, the production of hydroxyacetoneand HCHO were affected by water vapor as well as the initial NO/MACR ratio. The yields ofHCHO were higher under humid conditions than that under dry condition. The yields ofhydroxyacetone were higher under humid conditions at low-NOx level, while lower athigh-NOx level. The reasonable explanation for the lower hydroxyacetone yield underhumid conditions at high-NOx level is that water vapor promotes the production ofmethacrolein nitrate in the reaction of HOCH2C(CH3)(OO.)CHO with NO due to the peroxyradical-water complex formation, which was evidenced by calculational results. And theminimum equilibrium constant of this water complex formation was estimated to be1.89 × 10−18 cm3/molecule. These results provide new insights into the MACR oxidationmechanismand the effects of water vapor.