Portland State University. Environmental Sciences and Resources Ph. D. Program
Robert J. O'Brien
Date of Publication
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources: Chemistry
Environmental Science and Management
Atmospheric ozone -- Mathematical models, Photochemical smog -- Mathematical models, Computer simulation
2, xiv, 211 leaves: ill. 28 cm.
Photochemically produced ozone represents a worldwide enviromental hazard. Controlling ozone formation in polluted air requires control of hydrocarbon and nitrogen oxides precursors. The degree of control can be established with the chemical model of the reacting species. A hydrocarbon-specific photochemical ozone model is developed, based upon a minimum set of chemical equations. This model eliminates the need for the traditional "brute force" approach to integrate systems of tens or even hundreds of simultaneous differential equations. We have sought to develop the full kinetic potential for simplification which this chemical system may have. Key features of the model are reaction of parent hydrocarbon with hydroxyl radical (OH) to produce products, which themselves react with OH or are photodissociated. These basic steps are summarized by three rate parameters which describe NO photooxidation and ultimate accumulation of ozone. Since the mechanism may be solved in a closed form, it is a simple matter to evaluate the rate parameters for any hydrocarbon from smog chamber data. This evaluation can be carried out by analysis of data in NO photooxidation regime, before ozone begins to accumulate. The simple model for NO photooxidation is transformed to give an equation which describes the number of NO conversions per hydrocarbon decay, independent of time or of hydroxyl radical concentration. Comparison of the rate parameters determined from existing smog chamber data for n-butane and propene shows a very good agreement with explicit mechanisms for these extensively studied hydrocarbons. Rate parameters have been determined for a number of less studied hydrocarbons as well.
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