Theoretical investigation on the degradation of methyl vinyl ketone initiated by •OH and •Cl in the atmosphere and aqueous particles: Mechanism, kinetics, and environmental impact analysis

The absence of studies on the tropospheric reaction mechanism of unsaturated ketones increases the difficulty for the accurate assessment of their environmental fate. Herein, the gaseous and aqueous chemistry of methyl vinyl ketone (MVK) with center dot Cl and center dot OH, as well as the ensuing radical (e.g., chloroperoxy and hydroxyperoxy radicals) reactions are investigated from a theoretical perspective. A new pathway for the formation of alkoxyl radicals from peroxyl radicals is presumed. The reaction activity of alkoxyl radicals takes the order of beta-scission > with O-2 > with H2O > Russell mechanism. The aqueous environment shows the negative solvent effect on these two systems. The polarization of the proportion of the addition and abstraction reactions is intensified by the solvent effect. Although the rate constants k(MVK-Cl) > kMVK-OH > k(MVK-O3), center dot OH-induced MVK reaction is still the dominant sink of MVK. If the effect of center dot Cl is ignored, the atmospheric lifetimes of MVK will be overestimated by 12% and even more. The detailed reaction mechanisms and product information for the reaction of center dot Cl with MVK are calculated for the first time. Low volatility oxygenated products (such as organic acids, alpha-dicarbonyls, and some C-4 multifunctional molecules) produced in the title reactions may be an important bridge between unsaturated ketone and aqSOA. An increased eco-toxicity can occur from MVK to its degradation products in the center dot Cl-MVK system, highlighting the necessity in the research of LMW unsaturated hydrocarbon on environmental risk assessment.

Automated summary

This study investigates the tropospheric reaction mechanism of unsaturated ketones from a theoretical perspective, proposing a new pathway for the formation of alkoxyl radicals and highlighting the negative solvent effect in the aqueous environment. The reaction of methyl vinyl ketone (MVK) with •OH remains the dominant sink, with potential eco-toxicity implications in the degradation products of the •Cl-MVK system.