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A vehicle emissions test program was conducted to evaluate the impact of gasoline RVP reduction on CO emissions under conditions that are typical of CO exceedance days in Las Vegas and Los Angeles. Test results showed that CO emissions were reduced in the Las Vegas fleet when RVP was changed from 12 to 9 psi. In the Los Angeles fleet, the results were less consistent, perhaps due to the poorer integrity of evaporative emissions control systems on these vehicles. This suggests that an optimum emissions control strategy might include both RVP reduction and an effective vehicle inspection and maintenance (I&M) program.

Voluntary RFG opt-in and use of reduced-RVP gasoline are two fuel options being considered in several ozone nonattainment areas. This paper describes methods for evaluating the relative benefits of these two options, with specific application in the Southeast Michigan area. Currently, the most defensible approach for estimating relative emissions reduction benefits of gasoline modifications utilizes a hybrid of two EPA models: MOBILE5a and the Complex Model. By employing appropriate fuel compositions, this hybrid approach showed that reduced-RVP gasoline was nearly as effective as RFG in reducing total VOC emissions in Southeast Michigan-both near-term and long-term. With both gasoline options, most of the VOC benefit arises from lower nonexhaust emissions, caused by reduced RVP levels.