On-Road Remote Sensing of Heavy-duty Diesel Truck Emissions in the Austin-San Marcos Area : August 1998

In the summer of 1998, the University of Denver conducted a remote sensing study in the Austin-San Marcos, Texas area. The focus of the study was to measure the ratios of CO, HC, and NO to CO 2 and to get percent opacity readings for heavy-duty diesel trucks with elevated exhaust. We calculated the grams of CO, HC, and NO per kilogram of fuel combusted from the ratios as would be observed by probing the exhaust. In the process of measuring the ratios, the remote sensing unit results are independent of water and excess oxygen in the tailpipe not involved in combustion. The remote sensing unit also reports percent opacity from the amount of transmitted light at a wavelength of 3.9 µm from the source. The data show, on average, a correlation between high CO emissions and reported opacity. For the measurements of CO, HC, and NO there were 389 valid readings for each. The mean concentrations in grams of pollutant/kilogram fuel were 21.2, 1.1, and 14.0 and the medians were 9.7, 0.77, and 12.5 respectively. The fleet of these heavy-duty diesel trucks exhibits a distribution that is close to normal where the top 20% of the polluters account for approximately 35% of the total emissions. This observation contrasts with data from automobiles with gasoline combustion engines, their distribution is gamma where the top 10% of the fleet is generally responsible for approximately 50% of the total emissions. Percent opacities were measured with 314 valid measurements. The mean percent opacity was 0.9 and the median was 0.7. Compared to the ratios, there are fewer valid measurements for opacities than for the ratios, this is because many of the smoke plumes where very heavy which did not allow for a significant amount of transmission of light so the opacity measurement is rendered by the software as " invalid ". The real mean and median my be slightly higher, but with comparison to other data from opacities taken with this instrument the numbers will be appropriate. We compared our data from Texas to other data from Switzerland, Hong Kong, Pennsylvania, and California where previous fieldwork was done with diesel powered vehicles and found that the values that were calculated for CO, HC, NO and opacities are extremely similar.