Modeling and measurement of vehicle emissions from roadways

Under project 283, both experimental and model development work in air pollution research near roadways was considered. First, the original TXLINE model was modified so that it was suitable for use in modeling finite line sources. This modification enables the model to be used in modeling pollutant dispersion on curved roads and other types of scenarios for which an infinite line source model would not be applicable. This modification also allows the model to be used in predicting pollutant concentrations upwind of a roadway. The next research area considered was the revision of the original Texas intersection model, TEXIN. The original model had several limitations which inhibited its use in a large number of cases. With the revised version, many of these limitations are no longer present. T-intersections are specifically treated by appropriately assigning internal variables. Improved emission factor estimates are obtained with MOBILE3. MOBILE3 allows the user enhanced flexibility in describing the vehicle distribution along with anti-tampering options and inspection/maintenance programs. The user may choose either the CMA Operations and Design algorithm or the CMA Planning Procedure to analyze traffic flow at the intersection. The model exhibits very good accuracy for areas not surrounded by tall buildings. Finally, the collection of a large experimental data base was performed under the project. Data on meteorology, traffic, and pollutant concentrations were obtained in Houston, Texas. These data were used in the mass balance technique to estimate carbon monoxide emission factors which were then compared to the simulated factors obtained by the EPA model MOBILE3. In general, the MOBILE3 simulations yielded lower emission rates that those calculated by the mass balance. The primary purpose of the data base is the improvement and development of future roadway air quality models. In order to facilitate this process, the data base is available to the public on standard nine-track tape. Fifteen minute and hourly averages are printed in Appendix K, which is bound in a separate volume of this report (A).