Experimental studies of the kinetics of the OH-initiated oxidation of α - and β -pinene

The chemical mechanism of the oxidation of α - and β -pinene is a subject of considerable interest in atmospheric chemistry. These hydrocarbons are emitted into the atmosphere by various types of vegetation, and can contribute significantly to the production of ozone in the troposphere because of their high reactivity. The accuracy of urban and regional air quality models thus depends on a complete understanding of their oxidation mechanisms under a variety of conditions. Results of laboratory investigations of the mechanisms of the OH-initiated oxidation of α - and β -pinene in the presence of NO using discharge-flow techniques will be presented. Indirect measurements of the rate constant for the reaction of pinene-based hydroxyalkyl peroxy radicals with NO will be discussed. The measured OH radical concentration profile in the presence of NO was compared to simulations based on various proposed oxidation mechanisms for α - and β -pinene in order to determine the mechanism that best describes the observed radical propagation. These experiments provide a measurement of the relative efficiency of radical propagation by each biogenic hydrocarbon in the production of tropospheric ozone.