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Welcome to ZEV Help! Your Guide to Zero-Emission Commercial Vehicles

NOx regulation history and EPA/CARB convergence in 2027

EPA27 is the largest regulatory change since 2010

Regulatory requirements for NOx and PM have remained flat for over 10 years

For 2027, EPA NOx limits reduced by 82% from 0.2 to .035 g NOx/hp*hr

Emissions useful life requirements increased from 435k miles to 650k miles for Heavy Duty and from 185k miles to 350k miles for Medium Duty

Emissions useful life refers to the regulatory period in years or miles for which vehicles must meet emissions standards

NOx Regulation EPA and CARB Convergence

EPA24 NOx = .2 g NOx → EPA27 = .035g NOx (70% reduction)

CARB24 NOx = .05g nox (CARB asking EPA for a waiver to enforce this Nox value, they need permission to deviate from the EPA rule in 2024-2026) → CARB27 = .035g Nox

EPA wrote in a provision for EPA27 regulation that if  manufactures can release compliant Heavy Duty (12L+) product in Jan 2026, the engine manufacturers can meet .05g Nox and earn NOx credits for a whole year against .2g NOx (1.5g Nox worth of credits for each product sold). Those credits can then be spent on any MD or HD product for ~10 yrs. This is being called the 2026 Pull Ahead provision. 

CARB24 Omnibus regulation has a legacy provision that allows engine manufacturers to sell into CARB states (CA is the only one for 2024, several others come online in 2025) legacy product that is .2g NOx compliant not .05g NOx, by a certain percentage of compliant product. There is an equation for Engine Manufactures to use to calculate the volume of allowable legacy product to sell into CA or CARB states. This applies to MD and HD engines. These legacy sales also have to consume NOx credits and also come with a monetary surcharge. 

References:

https://www.epa.gov/regulations-emissions-vehicles-and-engines/final-rule-and-related-materials-control-air-pollution

https://ww2.arb.ca.gov/rulemaking/2020/hdomnibuslownox