On April 21, 2023, the Air Quality Control Commission (AQCC) adopted revisions to Regulation 20 which came into effect on June 14, 2023 and added the HD Low NOx regulation to Colorado (Part E of Regulation 20). This regulation provides limits on the amount of nitrogen oxides (NOx), carbon dioxide (CO2), hydrocarbons, carbon monoxide (CO), and particulate matter (PM) that heavy duty vehicles are allowed to emit.
The HD Low NOx rule applies to model year 2027 and subsequent model year vehicles with a GVWR of 14,001 pounds or greater that are offered for sale or lease in Colorado. Certain transit buses and emergency vehicles are exempt.
Automakers can submit their annual vehicle sales reports via email to cdphe_colevzev@state.co.us.
If you have any questions regarding HD Low NOx, please reach out to us via email at cdphe_colevzev@state.co.us.