Peroxy radicals form in the atmospheric oxidation of nearly every volatile organic compound (VOC). Their competing fates propagate or terminate free radical chemistry in the troposphere. Atomic chlorine is a minor tropospheric oxidant, found in marine and coastal regions, which reacts with volatile alkenes to yield chlorine-substituted peroxy radicals. In this work, we present the near-infrared absorption spectra of peroxy radicals formed in the chorine-initiated oxidation of a variety of VOCs including isoprene, the most important nonmethane hydrocarbon emitted into the troposphere. We use cavity ringdown spectroscopy to observe the weak A�X electronic transition of peroxy radicals in the near-infrared region. By monitoring the temporal decay of absorption features under varying radical environments, we report rate constants for the self reaction of chlorine-substituted peroxy radicals as well as their dominant atmospheric fates: reaction with HO2 and NO. Reaction with HO2 is important in pristine environments while reaction with NO dominates in polluted regions. We compare our results to those available for hydroxyl-substituted and alkyl peroxy radicals to elucidate the effect of chlorine substitution on peroxy radical reactivity. To our knowledge, these results report the first near-infrared absorption spectrum of a peroxy radical derived from isoprene oxidation. The real-time kinetic measurements of the reaction with HO2 and NO provide insight into the highly atmospherically relevant isoprene system.

Kinetics and near-infrared spectroscopy of chlorine-substituted peroxy radicals

248th National Meeting (2014)

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