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US EPA finalizes Multi-Pollutant Emissions Standards for MY 2027 light-duty vehicles

20 March 2024

The US Environmental Protection Agency (EPA) announced the final “Multi Pollutant Emissions Standards for Model Years 2027 and Later Light-Duty and Medium-Duty Vehicles”. The regulation, proposed in April 2023, includes two components:

The finalized emission standards are marginally less stringent compared to the April 2023 proposal.

GHG Emission Standards. For light-duty vehicles, the EPA projects that the standards will result in an industry-wide average target for the light-duty fleet of 85 g/mi of CO2 in MY 2032, Table 1, representing a nearly 50% reduction in projected fleet average emissions target levels relative to the existing MY 2026 standards.

Table 1. Light-duty vehicle GHG standards: Projected targets, by regulatory class
CO2 g/mi
Total Light-Duty Fleet17015313611910285

For medium-duty vehicles (MDV), the EPA projects that the new standards will result in an average target of 274 g/mi of CO2 by MY 2032, Table 2, representing a 44% reduction in projected fleet average emissions target levels relative to the existing MY 2026 standards.

Table 2. Medium-duty vehicle GHG standards: Projected targets, by regulatory class
CO2 g/mi
Total Medium-Duty Fleet461453408353314274

The GHG emission standards are intended to accelerate the uptake of electric vehicles. The EPA projects that from MYs 2030-2032 manufacturers would produce battery electric vehicles (BEV) for about 30% to 56% of new light-duty vehicle sales—depending on the scenario—and about 20% to 32% of new medium-duty vehicle sales.

The EPA also projects an increase in the availability of hybrid electric vehicles, plug-in hybrid electric vehicles, as well as more fuel efficient gasoline vehicles.

CAFE Standards. In addition to EPA GHG emission standards, manufacturers must meet CAFE fuel economy standards issued by the National Highway Traffic Safety Administration (NHTSA). CAFE standards for MY 2027-2032 vehicles were proposed in August 2023 but have not yet been finalized.

One difference between the GHG and CAFE regulations is that while BEVs are considered zero-emission vehicles for the purpose of EPA GHG regulations, they are not considered zero-fuel-consumption vehicles for the purpose of NHTSA CAFE regulations. Under CAFE, the fuel economy of electric vehicles is established using the petroleum-equivalent fuel economy calculation (PEF), the methodology of which is determined by the Department of Energy (DOE). Under a DOE method adopted in 2000, the PEF for EVs that do not have any petroleum-powered accessories was 82,049 Wh per gallon of gasoline.

On March 18, 2024, the DOE published a final rule revising the PEF calculation. The new PEF calculation, based on life-cycle approach for electricity production, produces lower EV fuel economy values, making it harder for manufacturers to meet CAFE standards by increasing the EV share in their vehicle fleet. The new PEF values decrease with the vehicle model year:

The above final PEF values are still higher compared to the DOE proposal of April 2023, which called for a PEF value of 23,160 Wh/gal effective from MY 2027.

Tier 4 Emission Standards. The EPA finalized “Tier 4” criteria pollutant emissions standards for non-methane organic gases (NMOG), NOx, PM, and other criteria pollutants. For light-duty vehicles, the Tier 4 NMOG+NOx standards will phase down to a fleet average level of 15 mg/mi by MY 2032, representing a 50% reduction from the existing 30 mg/mi Tier 3 standard. For MDVs, the Tier 4 NMOG+NOx standards will require a fleet average level of 75 mg/mi by MY 2033, representing a 58% to 70% reduction from the respective Tier 3 standards for Class 2b and Class 3 vehicles, Table 3.

Table 3. NMOG+NOx fleet-average emissions standards, mg/mi
Model YearLight-Duty VehiclesMedium-Duty Vehicles
Class 2bClass 3
* Existing Tier 3 standards

The NMOG+NOx standards continue the emissions certification “bin” structure approach used in prior programs. The Tier 4 standards add more bin resolution at low-emission bins and eliminate the highest certification bins to disallow production of the highest-emitting vehicles. The standards must be met across four driving cycles (FTP, US06, SC03, HFET) to ensure robust emissions control over a wide range of in-use driving conditions.

For both light-duty and medium-duty vehicles, the EPA finalized a PM standard of 0.5 mg/mi to be met across three test cycles, including a cold temperature (-7°C) test. The PM standard is a per-vehicle cap (not a fleet average) and will be fully phased-in by MY 2030 for light-duty vehicles and by MY 2031 for MDVs. The EPA projects that to meet the PM standard, manufacturers will widely utilize gasoline particulate filters on vehicles with internal combustion engines.

The Tier 4 standards also include stronger standards for CO of 1.7 g/mi for light-duty vehicles and 3.2 g/mi for MDVs.

The Tier 4 standards include phase-in implementation schedules. For light-duty vehicles and trucks (GVWR < 6000 lbs), 20% of vehicles must meet Tier 4 standards in 2027, 40% in 2028, 60% in 2029, and 100% in 2030.

Source: US EPA