THE EVALUATION OF SOME PHOTOCHEMICAL SMOG REACTION-MECHANISMS .2. INITIAL ADDITION OF ALKANES AND ALKENES

New experimental results from the CSIRO outdoor smog chambers are used to evaluate four widely-used photochemical reaction mechanisms. When alkanes are added to a smog chamber base loading of synthetic exhaust, increasing the initial ppmC content by 57%, it is found that the concentration of smog produced (SP) is reduced during the light-limited regime typically by 17-28%. All four models predict that SP concentrations under these conditions will increase (by 1-20%, depending on the model and the alkane used). It is argued that the inclusion of recently verified mechanisms for alkyl nitrate formation will improve model predictive ability. Alkane addition to gasoline increases both the rate of formation of SP and the maximum value and this is reflected in the model predictions. The effect of alkene addition to the synthetic exhaust base loading is to increase sharply the rate of SP formation. Final SP values, however, are limited by the available NO(x) levels in the latter stages of the experiments. Addition of an extra amount of synthetic exhaust to the synthetic exhaust base loading increases both the rate of formation of SP and the maximum value. Overall the reaction mechanisms' performance is good to excellent. The CB-III and Caltech models performed better generally than the CB-XR and CB-IV models for the 16 experiments examined.