Ozonolysis of alkenes is one of the major OH radical production channels in the troposphere. Production of the OH radical involves isomerization of a Criegee intermediate (CI) into a peroxide and its subsequent decomposition. In the case of trans- and cis-2-butene, acetaldehyde oxide CH3CHOO (CI) isomerizes into vinylhydroperoxide and subsequent decomposition yields OH and vinoxy radicals. However, the fate of the vinoxy radical in the troposphere has not yet been completely elucidated and further study of its reactions and products is necessary. In this work, we use a flow reactor and cavity ring-down spectroscopy to directly observe and measure the concentration of vinoxy radicals and formaldehyde (HCHO) produced from ozonolysis of trans- and cis-2-butene under several reaction conditions. Reactions without significant presence of O2 show that the yield of HCHO from both cis- and trans-2-butene is similar at ~0.18. However, the yield of vinoxy radical from cis-2-butene ozonolysis is around 60% of that from trans-2-butene ozonolysis, indicating HCHO production from both syn- and anti-CH3CHOO. In addition, measurements of vinoxy radicals and formaldehyde under excess O2 and at short reaction times were performed. The use of 2-butene ozonolysis mechanisms to simulate the experimental measurements provided more information on the possible reaction pathways of the vinoxy radical and its contribution to the formation of additional OH radicals, formaldehyde, and glyoxal.

Direct measurements of vinoxy radicals and formaldehyde from ozonolysis of trans- and cis-2-butenes: New insights into OH radical formation and secondary chemistry

2019 Fall National Meeting

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