Attorney General Bonta, California Air Resources Board Call on EPA to Move Forward with Emission Standards for Light- and Medium-Duty Vehicles

OAKLAND — Leading a coalition of 19 states and 4 cities, California Attorney General Rob Bonta and the California Air Resources Board (CARB) today submitted a comment letter to the U.S. Environmental Protection Agency (EPA) opposing its proposed rule that would delay implementation of the Tier 4 emissions standards for light-duty and medium-duty vehicles. If finalized, EPA’s proposal would give manufacturers two additional years before they must begin implementing these health-protective standards. Under the current, state-of-the-art “Tier 4” standards, which EPA adopted in 2024, manufacturers must ensure that vehicles emit fewer harmful pollutants, including nitrogen oxides, particulate matter, hydrocarbons, and carbon monoxide. When it adopted these standards, EPA gave manufacturers sufficient lead time before the standards would begin to be phased in and several additional years before full implementation of the standards is required. In accordance with this schedule, manufacturers are required to start implementing the standards with their model year 2027 vehicles and will have to obtain Tier 4 certification for all light-duty vehicles by 2030 and for all medium-duty vehicles by 2031. Now, EPA has proposed to delay the start of this phase-in schedule for two years, which would delay the health protections the standards provide. In the comment letter, Attorney General Bonta, CARB, and the coalition assert that EPA’s proposal to delay this compliance schedule, such that manufacturers are not required to take any action until they begin producing model year 2029 vehicles, would harm public health and welfare by delaying the benefits of stricter air pollutant emissions standards. 

“Every day the EPA delays the phase-in schedule, the harms to the public will continue to grow. This especially jeopardizes our most vulnerable communities, which bear the brunt of transportation-related pollution and suffer the resulting health consequences,” said Attorney General Bonta. “The longer EPA delays these requirements, the greater the human and economic costs will be on its watch. The EPA must move forward with the phase-in schedule immediately.”

“Apparently, EPA thinks 2 plus 2 doesn’t equal Tier 4. But zeroing out the value of human life and ignoring the facts doesn’t change them,” said CARB Executive Officer Dr. Steven Cliff. “Delaying these standards will put more harmful pollution into the air, increase health care costs, and lead to more preventable illnesses and premature deaths.”

Air pollution from motor vehicles continues to impact public health, welfare, and the environment. Motor vehicle emissions contribute to ozone, increased levels of particulate matter, and air toxics, which are linked to premature deaths and other serious health impacts, including respiratory illness, cardiovascular problems, and cancer. Addressing these public health and welfare risks requires reductions in air pollutants from the transportation sector, including the reductions EPA adopted in the 2024 Multi-Pollutant Rule. EPA projected that the final rule’s reductions of greenhouse gases, criteria pollutants, and air toxics would result in $270 billion net benefits by 2055 and would eliminate 410 million metric tons of carbon dioxide, 36,000 tons of NOx, 8,700 tons of particulate matter, and 2,300 tons of benzene that otherwise would have been emitted by vehicles. Under the Trump Administration, EPA has already repealed federal greenhouse gas standards for vehicles, and Attorney General Bonta, CARB and Governor Newsom are co-leading a coalition of states, local governments, and regulatory agencies that are currently challenging that action in court. Now EPA seeks to delay the implementation of its criteria and toxic pollutant standards, which would similarly erase important health and welfare benefits from the 2024 rulemaking.

In the letter, the attorneys general and cities assert that:

• EPA has failed to support with any evidence its claims that compliance with the Tier 4 standards is infeasible. In fact, the Tier 4 standards are still feasible and cost-effective based on the lengthy phase-in schedule and the flexible compliance pathways outlined in the 2024 rule, including low-cost, off-the-shelf controls for internal combustion engines.
• EPA failed to conduct any air quality modeling, nor did EPA make any attempts to consider the economic value of the negative impacts of delaying the Tier 4 standards on air quality, and, by extension, public health and welfare.
• The Clean Air Act does not allow EPA to reverse course and weaken criteria and toxic air pollutant standards. It also does not authorize EPA to make it harder for States to meet federal air quality standards. Thus, this proposal, if finalized, would be unlawful. 

In submitting the comment letter, Attorney General Bonta and CARB lead the attorneys general and cities of Colorado, Connecticut, Delaware, Hawai’i, Illinois, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Jersey, New York, North Carolina, Oregon, Rhode Island, Washington, Wisconsin, and the District of Columbia; the Chief Legal Officers of the City of Chicago, Illinois; the City of New York, New York; the City and County of Denver, Colorado; and the City and County of San Francisco, California.