Studies in Photochemical Smog Chemistry: I. Atmospheric Chemistry of Toluene. II. Analysis of Chemical Reaction Mechanisms for Photochemical Smog

This study focuses on two related topics in the gas phase organic chemistry of importance in urban air pollution. Part I describes an experimental and modeling effort aimed at developing a new explicit reaction mechanism for the atmospheric photooxidation of toluene. This mechanism is tested using experimental data from both indoor and outdoor smog chamber facilities. The predictions of the new reaction mechanism are found to be in good agreement with both sets of experimental data. Additional simulations performed with the new mechanism are used to investigate various mechanistic paths, and to gain insight into areas where our understanding is not complete. The outdoor experimental facility, which was built to provide the second set of experimental data, consists of a 65 cubic meter teflon smog chamber together with full instrumentation capable of measuring ozone, nitrogen dioxide, nitric oxide, peroxyacetyl nitrate (PAN), carbon monoxide, relative humidity, temperature, aerosol size distributions, and of course toluene and its photooxidation products. In Part II, we present a theoretical analysis of lumped chemical reaction mechanisms for photochemical smog. Included is a description of a new counter species analysis technique which can be used to analyze any complex chemical reaction mechanism. When applied to mechanisms for photochemical smog, this analysis is shown capable of providing answers to previously inaccessible questions such as the relative contributions of individual organics to photochemical ozone formation. The counter species analysis is applied to six existing mechanisms for photochemical smog to determine why they predict substantially different degrees of emission controls to achieve the same desired air quality under identical conditions. For each mechanism critical areas are identified that when altered bring the predictions of the various mechanisms into much closer agreement. Finally, a new lumped mechanism for photochemical smog is developed and tested against experimental data from two smog chamber facilities. Advantages of this mechanism relative to the existing lumped mechanisms are discussed.