EVALUATION OF A DETAILED GAS-PHASE ATMOSPHERIC REACTION-MECHANISM USING ENVIRONMENTAL CHAMBER DATA

This paper describes an evaluation of the performance of a detailed gas-phase reaction mechanism in simulating the results of 561 experiments carried out in four different environmental chambers. The experiments included background air, NO(x)-air, CO-NO(x)-air and aldehyde-air irradiations used for chamber characterization, NO(x)-air irradiations of single organics as well as simple and complex organic mixtures, and irradiations of auto exhaust. The methods used to represent the major chamber effects and the lighting characteristics in the model simulations of the experiments are described and their associated uncertainties are discussed. Statistical measures of the performance of the mechanism in simulating results of the various types of experiments are summarized and discussed. The mechanism was able to predict maximum ozone yields and rates of NO oxidation to within +/- 30% for 63% of the experiments modeled, and to within +/- 50% for 85% of the runs. There is a slight bias (approximately 15%) towards overprediction of ozone in mixture runs. Although there are cases where the simulations suggest possible problems with the gas-phase mechanism, much of the variability in the goodness of the fits could be attributed to uncertainties in chamber effects. It is concluded that better characterization of chamber conditions are needed if more comprehensive tests of atmospheric photochemical mechanisms are desired.