An on-road motor vehicle emissions inventory for Denver: an efficient alternative to modeling

Emission inventories from mobile sources have traditionally been obtained through computational modeling. This method, however, has intrinsic shortcomings in that the factors used incorporate only a limited amount of real-world observations. The agreement between model predictions and measurements has often been poor. Recently, a fuel-based method of obtaining on-road emissions inventories has been developed. This technique calculates emission factors in grams of pollutant per unit of fuel used (kg, gallons or l) from remote sensing measurements. Combining these factors with fuel use data, available from tax records, results in a fuel-based emission inventory. This method for obtaining emission inventories is very economical and an ideal alternative for locations lacking the resources to develop an emissions model. We have used this routine to calculate CO, HC and NO on-road running exhaust emissions inventories for the Denver Metropolitan area during several years when the enhanced I/M program has been in place. These calculations indicate a continually decreasing inventory over the 6 yr study period. The calculations are also compared with results from the recent MOBILE6 model. The modeled inventories are 30–70% higher, 40% lower, and 40–80% higher for CO, HC and NO, respectively.