Significance of HOₓ and peroxides production due to alkene ozonolysis during fall and winter: A modeling study

In an attempt to identify new mechanisms for the generation of oxidants during fall and winter, we carried out a modeling investigation in which ozonolysis reactions of alkenes that were primarily anthropogenic in origin were considered. Our results indicate that the ozonolysis reactions of these molecules can be the major sources of HOₓ, H₂O₂, and organic peroxides during the night and therefore especially during dark seasons. These O3-initiated oxidation reactions produce more peroxy radicals than those initiated by HO or NO3. This increase in RO₂ also results in an increase in HO, HO₂, and H₂O₂. The direct HO formation pathways by ozonolysis of alkenes can form more HO radicals than that from the reaction of O(1D) + H₂O during the dark seasons. This additional source of HO can augment significantly atmospheric oxidation. H₂O₂ formation by ozonolysis also appears to be the most important dark season tropospheric sources of this oxidant. Our modeling results suggest that the existence of pollutant hydrocarbons and trace amount of biogenically produced terpenes can also lead to important production of HOₓ, H₂O₂, and organic peroxides. Substantially enhanced gas-phase production of H₂O₂ and organic peroxides due to ozonolysis reactions can cause significant liquid-phase oxidation of S(IV) to S(VI), and hence the role of ozonolysis reactions can be important for the sulfur conversion studies