Protection of the Stratospheric Ozone: Alternatives for the Motor Vehicle Air Conditioning Sector Under the Significant New Alternatives Policy (SNAP) Program

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Under section 612 of the Clean Air Act, the Environmental Protection Agency (EPA) reviews and lists as acceptable alternatives to ozone-depleting substances (ODS). In 2006, EPA proposed to list R-744 (CO 2 ) as "acceptable with use conditions" as a substitute for CFC-12 in the motor vehicle air conditioning (MVAC) end-use within the refrigeration and air-conditioning sector. When using CO 2 as a refrigerant, MVAC systems would be required to use the refrigerant according to those legally enforceable conditions. EPA proposed use conditions because of the potential risk of exposure to elevated concentrations of CO 2 within the passenger compartment if there was a leak of the MVAC system. Elevated CO 2 levels could cause passengers, and of particular concern, the driver, to become drowsy. Since the time of the proposed rule, additional information regarding the effects of short-term CO 2 exposures has become available and EPA is now making that information available to the public. As noted in the proposed rule, EPA is considering whether to establish a breathing zone ceiling and this short-term exposure information is relevant to EPA's decision on this issue. In addition, EPA is provi