Development of a Generalized Kinetic Mechanism for Photochemical Smog

In this dissertation a generalized kinetic mechanism for photochemical smog is formulated and validated. There are two basic objectives for pursuing this work. First, kinetic mechanisms are a critical component of airshed simulation models whose uses include the evaluation of alternative control strategies for photochemical smog. Second, kinetic mechanisms provide a means of understanding the chemistry of smog formation. In addition to developing the kinetic mechanism, extensive consideration is given here to further experimental studies of the kinetics of elementary reactions and to procedural aspects of smog chamber experiments which will aid in reducing uncertainty in future mathematical simulation studies. The most important feature of the kinetic mechanism which 1s presented in Chapter I lies in its general nature; that is, the mechanism has been written so as to be applicable to a large number of hydrocarbons -- and, ultimately, the entire atmospheric hydrocarbon mix -- rather than just a specific hydrocarbon such as propylene. The rationale for the lumping procedure is described in detail. By design the resultant mechanism takes advantage of the general features typical of smog formation to maintain at a minimum the number of reactions and species included while at the same time retaining a high degree of detail, especially as concerns the chemistry of the inorganic species. In essence a careful balance between compactness of form and accuracy of prediction is sought. The mechanism is then validated using n-butane-NOx, propylene-NOx, and n-butane-propylene- NOx smog chamber data at 13 different sets of initial reactant concentrations and a wide variety of hydrocarbon to NOx ratios. Several sources of potential uncertainty in the predictions of the mechanism are discussed. Of these the two most serious -- and the two most amenable to correction -- are gaps in our knowledge of rate constants and mechanisms of key elementary reactions and effects related to smog chamber systems which either alter or incorrectly monitor the course of smog formation in controlled experimenta1 studies. These sources of uncertainty along with recommendations for future studies to minimize them are the topics of Chapters II and III.