Review of UCR (University of California-Riverside) Protocol for Determination of OH (Hydroxyl Radicals) Rate Constants with VOC (Volatile Organic Chemicals) and Its Applicability to Predict Photochemical Ozone Production

摘要

The experimental protocol for determining the rate constants for reactions of hydroxyl radicals (OH) with volatile organic chemicals (VOCs) as developed by the University of California-Riverside group is evaluated. Limits of detection and precision are discussed. The protocol is to be used as a measure of the ozone forming potential of a VOC; a compound with a high OH rate constant also very often produces high levels of ozone. Adaptations of the protocol for compounds containing halogen atoms are suggested. The protocol may not be applicable for compounds that do not produce RO2 and HO2 radicals such as carbon disulfide. Also, compounds that are free radical scavengers such as phenol, benzaldehyde and amines may not give high levels of ozone even though they may have a high rate of reaction with OH radicals. The long chained paraffins also present problems with the protocol since the RO2 radicals produced after reacting with OH radicals in air do not oxidize NO to NO2 but instead combine with the NO to form nitrates. When this occurs, it is recommended that the protocol be complemented with smog chamber experiments in order to establish the reactivities of VOCs.