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Air toxics: controlling mobile sources

Bumper to bumper traffic on a highway

Mobile sources of air pollution include passenger vehicles, heavy duty trucks, and other non-road sources such as construction equipment, aircraft, and locomotives. These sources contribute over one-third of Colorado’s air toxics emissions from human activity according to the EPA’s 2020 National Emissions Inventory. Fuel combustion from diesel-powered mobile sources emit air toxics such as polycyclic aromatic hydrocarbons, benzene, formaldehyde, acetaldehyde, acrolein, and 1,3-butadiene. 

Colorado has several programs in place to help to reduce air toxics emissions from mobile sources. These programs also help achieve lower greenhouse gas emissions and ground-level ozone precursor emissions.

Vehicle inspection and maintenance programs

Many vehicles registered in Colorado’s ozone nonattainment areas are periodically inspected with rapid screening tests conducted while driving or by taking the vehicle to an Air Care facility. These inspections ensure a vehicle's emission controls and engine function properly. Vehicle owners are responsible for any repairs needed to address emission deficiencies identified during the inspection.

Alternative fuels

Transitioning to lower greenhouse gas intensive fuels, such natural gas, and renewable energy, such as wind and solar, also help reduce air toxics. 

  • The Colorado Air Quality Control Commission has adopted several rules in Regulation 20 to increase sales of low- and zero-emission passenger vehicles and  light and medium duty trucks. These rules increase clean vehicle options for Coloradans. 
  • Additionally, the Air Quality Control Commission adopted the Advanced Clean Trucks and Low NOx rules in April 2023 and intends to propose a Clean Car rule later in 2023 all under Regulation 20. 
  • Multiple other programs address vehicle emissions and some provide financial incentives to help reduce the up-front costs associated with purchasing new alternatively fueled vehicles. Visit our Low and zero emission vehicles webpage to learn more.