On-Road Remote Sensing of Automobile Emissions in the Chicago Area: Year 6, September 2004

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Final Report prepared for CRC




The University of Denver has completed the first six years of a multi-year remote sensing study in the Chicago area, with measurements made in September of 1997 through 2000, 2002 and 2004. The remote sensor used in this study is capable of measuring the ratios of CO, HC, and NO to CO2 in motor vehicle exhaust. From these ratios, we calculate the percent concentrations of CO, CO2, HC and NO in the exhaust that would be observed by a tailpipe probe, corrected for water and any excess oxygen not involved in combustion. Mass emissions per mass or volume of fuel can also be determined. The system used in this study was 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.

The sixth year of this study involved fieldwork on September 20 - 23, 2004, conducted at the on-ramp from Algonquin Rd. to eastbound I-290 in northwest Chicago. For the 2004 measurements, a database was compiled containing 21,838 records for which the State of Illinois provided makes and model year information. All of these records contain valid measurements for at least CO and CO2. A total of 21,775 records contain valid measurements of CO, HC and NO. The database, as well as others compiled by the University of Denver, can be found at www.feat.biochem.du.edu.

The mean CO, HC and NO emissions for the fleet measured in the sixth year of this study were 0.17% (21.5 g/kg), 72 ppm (when a 20ppm offset is removed, 2.8 g/kg) and 236 ppm (3.3 g/kg) respectively. Compared to the means measured in 1997 of 0.45% (55.8 g/kg), 130 ppm (when a 80ppm offset is removed, 5.3 g/kg) and 400 ppm (5.5 g/kg) these are overall reductions of 61% for CO, 47% for HC and 40% for NO. It is also notable that these reductions have occurred while the fleet has aged a half a model year during this time.

The fleet emissions observed at the site in Chicago exhibited a skewed distribution, with most of the total emissions contributed by a small percentage of the measurements. The skewness of the measurement distribution has markedly increased since 1997 when half of the emissions for CO, HC and NO were from 6.7%, 13.2% and 11.2% of the measurements. In 2004 half of the emissions for CO, HC and NO were from 4.4%, 5.1% and 6.4% of the measurements. This is a result of the adding progressively lower emitting vehicles with each model year since 1997. Fleet emission levels for all three species continue to decline each year and there is emerging evidence that emission levels are better controlled during accelerations and decelerations as well. The NO emissions continue to show a steady decline in emissions at all VSP loads.

Having collected six data sets over an eight year period at the same time and location, it is possible to show the “deterioration” of specific model year fleets from one year to the next. When we restrict the fleet to only those model years observed during the first measurements in 1997 the 1983-1997 model year vehicles have had rather flat emissions with age, counter to the traditionally expected view of emissions deterioration. Another way of phrasing this is that the fleet fraction of gross emitters first seen in 1997 has remained the same for that model year grouping even though that original fleet has aged seven years and the remainder of that original fleet numbers on 6,220. It is unlikely that I/M or fuel programs are the reason for this observation. Continuing studies at the same site and at non I/M, non-special fuels sites should allow further insight to be gained as to the extent I/M programs and special fuels contribute to reducing motor vehicle fleet emissions deterioration compared with fleet turnover.