The California Air Resources Board (CARB) intends to propose modifications to California’s Alternative Diesel Fuels (ADF) regulation that will ensure that additives perform consistently with the U.S. state’s regulatory requirements.

These amendments may require additional testing of currently certified additives, among other steps, to ensure conformance with regulatory standards for currently certified additives and additives certified in the future.

As part of this amendment process, CARB may consider approving blends of renewable diesel with biodiesel (approximately R80/B20) for use by any blender to meet the NOx control requirements, in case additive availability is limited due to the regulatory changes.

CARB, through the University of California, Riverside, conducted emissions testing designed to determine, consistent with the emissions mitigation requirements of CARB’s Regulation on the Commercialization of Alternative Diesel Fuels (ADF regulation), that additives certified pursuant to that regulation are effective at mitigating biodiesel NOx emissions to equivalence with CARB diesel.

The testing conducted on 20% biodiesel blends (B20) showed that the additives failed to effectively mitigate to the regulatory standard. These results raised significant questions both as to the specific additives addressed by the testing and regarding how best to ensure appropriate performance of additives and formulations under the ADF regulation going forward.

California’s Alternative Diesel Fuels regulation is intended to create a framework for low-carbon, and lower-polluting, diesel fuel substitutes to enter the commercial market in California, while mitigating any potential environmental or public health impacts. ADFs are those alternative diesel fuels that do not have an established CARB fuel specification in place prior to 1 January 2016. The first ADF that is subject to in-use requirements under the ADF regulation is biodiesel.

CARB issued the product alert on 31 October 2019. Pending further notice, all California biodiesel producers, importers, and blenders may continue to use CARB certified NOx mitigation additives to comply with the ADF regulation’s NOx mitigation requirements. In order to ensure that regulated parties currently using certified NOx mitigation additives to comply with the ADF regulation have adequate time to transition to other compliance strategies in the event CARB considers and ultimately adopts regulatory amendments as described above, any changes to the existing additive certifications will not be effective prior to 1 January 2020.

The product alert does not affect biodiesel blends B5 and below, which represents about 70% of the California biodiesel market, as no mitigation is required for those blends.