and lead to widespread nonattainment in rural as well as urban areas of the eastern United States (Wolff 1996; Chameides et al. 1997). With the persistence of the ozone-pollution problem comes the need to develop new and innovative approaches to lowering ozone-precursor emissions. The federal RFG program is but one example of a new approach that is being promulgated to address this need.
In the formulation and testing of various blends of RFG, it became apparent that these blends could affect motor-vehicle emissions in various and subtle ways (AQIRP 1990; OTA 1990). In addition to affecting the total mass of VOC emissions, different RFGs could have different effects on the amounts of NOx and CO emitted by motor vehicles. They