A Comparison of Refueling Emissions Control With Onboard and Stage II Systems

A comparison of alternative methods for the control of motor vehicle refueling emissions indicates that Stage II control systems installed at gasoline service stations can provide greater control at lower cost than Onboard control systems installed on motor vehicles. In addition, Stage II control can be achieved with a shorter implementation schedule. Because of this advantage, Stage II controls can achieve more than twice the hydrocarbon reductions possible with Onboard systems during the next ten years, when additional reductions are needed to meet the ambient air quality standard for ozone.

Several assumptions are critical to a comparison of Stage II and Onboard controls. These include service station population and size cut-offs, whether “breathing loss” emissions are considered, system cost and lead time, and whether additional evaporative emission controls are considered under both Stage II and Onboard control programs. Recent comparisons of Stage II and Onboard control alternatives published by others have shown Onboard control to be relatively more attractive. However, an analysis of these other comparisons indicates that several of the critical assumptions were either inaccurate or unrealistic.