Review of EPA’s Analysis of the Emissions Impacts of Providing Regulatory Flexibility for E15

On March 21, 2019, the U.S. Environmental Protection Agency (EPA) published a Notice of Proposed Rulemaking addressing modifications to fuel regulations to provide flexibility for E15. The proposed flexibility for E15 blends involves extending the current 1 pound per square inch (psi) RVP tolerance available for E10 blends to E15. More specifically, the proposed E15 flexibility provisions would revise the current maximum allowable summertime RVP limit of 9 psi for E15 to 10 psi, the same limit that applies to E10 blends.

EPA has proposed, among other things, to modify its interpretation of Clean Air Act section 211(h)(4) as applying the 1.0 psi RVP tolerance to gasoline ethanol blends of 10% or more, and also to update its interpretation under section 211(f)(1) of what is “substantially similar” (“sub sim”) to certification fuel utilized in certification to include E15 at 10.0 psi. Specifically, EPA is proposing to find that E15, whether with an RVP of 9 or 10 psi, is substantially similar to the E10 fuel used in the certification of Tier 3 vehicles (which has an RVP specification of 9 psi).

EPA’s emissions analysis is comprised of (1) an evaluation of whether E15 is sub sim to E10 certification fuel; and (2) a discussion of the overall impact of the proposed rule. First, in analyzing whether E15 is substantially similar to E10 certification fuel, EPA evaluated the potential impacts of E15 relative to E10 on exhaust emissions, materials compatibility, and driveability. Overall, EPA found that the exhaust emissions impacts of E15 as compared to E10 would be slight, that there would be no impacts on driveability and materials compatibility, and that, consistent with its established practice, a fuel qualifies as sub sim if its volatility meets ASTM specifications. Based on this analysis, EPA concludes that E15 is substantially similar to E10 certification fuel. These findings are also consistent with those made previously by EPA in authorizing the use of E15 in model year (MY) 2001 and later vehicles.

Second, regarding the overall emissions impacts of the rule with respect to evaporative emissions, EPA observed that E15 at 10 psi is less volatile than E10 at 10 psi, which is the fuel it would likely replace. Therefore, the proposed rule would lower the volatility of in-use gasoline and reduce evaporative emissions. In addition, EPA finds that the additional dilution associated with E15 relative to E10 will reduce evaporative emissions of benzene, a toxic air contaminant. With respect to exhaust emissions, relying on the EPAct models, EPA suggested that E15 blends may result in slightly lower CO emissions, which can play a role in ozone formation, and slightly higher NOx and PM emissions.

This report provides input regarding EPA’s technical emissions analyses and conclusions that E15 is sub sim to E10 certification fuel, as well as the overall emissions impact of the proposed rule. The results of the review support EPA’s overall findings that E15 is substantially similar to E10 certification fuel and that any impacts of the proposed rule on emissions will be, at most, small. This conclusion that E15 and E10 will have similar emissions effects applies to Tier 3 vehicles certified using E10 as well as MY 2001 and later gasoline-fueled light-duty vehicles certified using E0. However, due to shortcomings in the EPAct study methodology on which EPA relies, this review also indicates that the small increases in exhaust emissions of some pollutants that EPA reports as possible from the proposed rule are less certain to exist than EPA asserts and may in fact not actually occur—EPA should acknowledge this uncertainty in the final rule. In addition, this review confirms that the reductions in general evaporative emissions as well as evaporative emissions of benzene and emissions of carbon monoxide that EPA suggests will in fact occur.