Comparison of auto emission measurement techniques

The Clark and Washoe Remote Sensing Study (CAWRSS) field season took place in September 1994. The study was designed to characterize the exhaust emissions of the on-road vehicle fleet in the two major urban centers of the State of Nevada. The air quality in Las Vegas (Clark County) and Reno (Washoe County) is significantly worse than the surrounding rural areas and vehicle emissions have been identified as one of the primary sources of the pollution. Inspection and maintenance programs, mandated by the federal government, have been implemented in both urban areas. The study compated the State-approved test, a no-load, two-speed idle test, to two other measurement techniques: remote sensing devices (RSDs) and the IM240 test, a loaded-mode test run on a dynamometer. Results were viewed from two different perspectives. Fleet-wide characteristics showed that concentrations of CO (%) measured with RSDs were higher than those obtained with the no-load idle tests. Characteristics of pollution distributions derived from the two techniques were similar in range and shape. Observations for individual vehicles were then compared. CAWRSS is in agreement with earlier studies in that high emitters in the idle test are also high emitters on-road.