The production of formaldehyde and hydroxyacetone in methacrolein photooxidation: New insights into mechanism and effects of water vapor  

作　　者：Yanan Xing Huan Li Liubin Huang Huihui Wu Hengqing Shen Zhongming Chen 

机构地区：[1]State Key Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University

出　　处：《Journal of Environmental Sciences》2018年第4期1-11,共11页环境科学学报（英文版）

基　　金：supported by the National Natural Science Foundation of China (Nos. 21477002, 41421064);the National Key Research and Development Program of China (No. 2016YFC0202704)

摘　　要：Methacrolein（MACR） is an abundant multifunctional carbonyl compound with high reactivity in the atmosphere. In this study, we investigated the hydroxyl radical initiated oxidation of MACR at various NO/MACR ratios（0 to 4.04） and relative humidities（＆lt; 3% to80%） using a flow tube. Meanwhile, a box model based on the Master Chemical Mechanism was performed to test our current understanding of the mechanism. In contrast to the reasonable predictions for hydroxyacetone production, the modeled yields of formaldehyde（HCHO） were twice higher than the experimental results. The discrepancy was ascribed to the existence of unconsidered non-HCHO forming channels in the chemistry of CH3-UC（=CH2）OO, which account for approx. 50%. In addition, the production of hydroxyacetone and HCHO were affected by water vapor as well as the initial NO/MACR ratio. The yields of HCHO were higher under humid conditions than that under dry condition. The yields of hydroxyacetone were higher under humid conditions at low-NOx level, while lower at high-NOxlevel. The reasonable explanation for the lower hydroxyacetone yield under humid conditions at high-NOx level is that water vapor promotes the production of Umethacrolein nitrate in the reaction of HOCH2 C（CH3）（OO）CHO with NO due to the peroxy radical-water complex formation, which was evidenced by calculational results. And the minimum equilibrium constant of this water complex formation was estimated to be 1.89 × 10 （-18） cm3/molecule. These results provide new insights into the MACR oxidation mechanism and the effects of water vapor.Methacrolein（MACR） is an abundant multifunctional carbonyl compound with high reactivity in the atmosphere. In this study, we investigated the hydroxyl radical initiated oxidation of MACR at various NO/MACR ratios（0 to 4.04） and relative humidities（＆lt; 3% to80%） using a flow tube. Meanwhile, a box model based on the Master Chemical Mechanism was performed to test our current understanding of the mechanism. In contrast to the reasonable predictions for hydroxyacetone production, the modeled yields of formaldehyde（HCHO） were twice higher than the experimental results. The discrepancy was ascribed to the existence of unconsidered non-HCHO forming channels in the chemistry of CH3-UC（=CH2）OO, which account for approx. 50%. In addition, the production of hydroxyacetone and HCHO were affected by water vapor as well as the initial NO/MACR ratio. The yields of HCHO were higher under humid conditions than that under dry condition. The yields of hydroxyacetone were higher under humid conditions at low-NOx level, while lower at high-NOxlevel. The reasonable explanation for the lower hydroxyacetone yield under humid conditions at high-NOx level is that water vapor promotes the production of Umethacrolein nitrate in the reaction of HOCH2 C（CH3）（OO）CHO with NO due to the peroxy radical-water complex formation, which was evidenced by calculational results. And the minimum equilibrium constant of this water complex formation was estimated to be 1.89 × 10 （-18） cm3/molecule. These results provide new insights into the MACR oxidation mechanism and the effects of water vapor.

关 键 词：Methacrolein Formaldehyde Hydroxyacetone NOx Water vapor Peroxy radical 

分 类 号：TQ224[化学工程—有机化工]