On-Road Remote Sensing of Automobile Emissions in the Chicago Area: Year 1

The University of Denver conducted a five-day remote sensing study in the Chicago area in the fall of 1997. The remote sensor used in this study is capable of measuring the ratios of CO, HC, and NO to CO 2 in motor vehicle exhaust. From these ratios, we calculate the percent concentrations of CO, CO 2 , HC and NO in motor vehicle exhaust which would be observed by a tailpipe probe, corrected for water and any excess oxygen not involved in combustion. The system used in this study was also configured to determine the speed and acceleration of the vehicle, and was accompanied by a video system to record the license plate of the vehicle. Five days of fieldwork were conducted at the on-ramp from Algonquin Rd. to southbound I-290 in west Chicago. A database was compiled containing 18,320 records for which the State of Illinois provided make and model year information. All of these records contained valid measurements for at least CO and CO 2 , and more than 17,500 contained measurements for HC and NO. The mean percent CO, HC, and NO were determined to be 0.45%, 0.021%, and 0.040%, respectively. These values are amongst the lowest we have observed for a statistically significant fleet, and are considerably lower than those for fleets previously measured in the Chicago area. The fleet emissions measured in this study exhibit a gamma distribution, with the dirtiest 10% of the fleet responsible for 61%, 44%, and 46% of the CO, HC, and NO emissions, respectively. Vehicle emissions as a function of acceleration revealed that fuel specific CO emissions are relatively independent of acceleration and that HC emissions show only a slight negative dependence. In contrast, the NO measurements made in this study showed a strong positive correlation on measured acceleration. There were a considerable number of repeat measurements in the database; only 58% of the measurements resulted from vehicles measured once. The remaining 42% of the measurements were of vehicles measured at least twice. By removing all of the repeat measurements from the database and allowing each vehicle to appear only once, we have shown that these repeat measurements are not skewing the results and that the full database is statistically representative of the actual fleet at the measurement site. This was the first year of a five-year continuing study to characterize motor vehicle emissions and deterioration in the Chicago area.