A model is developed to correct hot and cold start vehicle fractions for input to conventional emission factor models. The method is appropriate for microscale air quality analyses of urban freeways and arterials. It is based on the propositions that hot and cold start transient emissions are highest at engine start-up and gradually diminish to zero as engine and catalyst reach a stable operating temperature and that the distribution of vehicles on urban freeways and arterials in the warm-up phase of operation is skewed such that more vehicles are near the end of the phase than the beginning. Use of the ftp-75 split 27 percent hot and 21 percent cold starts may resulting significant overpredictions of air quality impacts for urban freeways. Corrected values of 1 and 5 percent, respectively, are predicted by the model.
Abstract