Air toxics: applicable laws and policies

Colorado State Capitol building dome interior

While air toxics are emitted from both human and natural sources, air toxics emitted from certain human sources are controlled by federal and state laws, regulations, and policies.

Federal Clean Air Act

The federal Clean Air Act amendments in 1990 directed the EPA to establish technology-based standards for major stationary sources of air toxics. As these technology-based standards are established, the EPA is required to periodically review the standards to account for changes in available technologies and work practices to reduce emissions. During this review, the EPA must also assess whether any risks remain for populations living near these air toxics sources. Clean Air Act amendments also established a framework to reduce priority air toxics emissions from smaller stationary sources and mobile sources that exist in urban areas. Colorado Department of Public Health and Environment implements these federal standards through permitting of emission sources, enforcement, and compliance. 

For mobile sources, the Clean Air Act provides authority for the EPA to reduce air toxics emissions through two main mechanisms. 

  • First, it provides the authority to modify fuel requirements such as the phaseout of leaded gasoline from passenger vehicles in 1973 and changes made in 2007 to reduce the amount of benzene in gasoline. 
  • Second, the EPA issues periodic updates to more comprehensive, multi-pollutant approaches for reducing air pollution emissions from vehicles through requirements for more efficient engines. For example, this work may include tailpipe standards and fleetwide fuel efficiency standards. 

Colorado air toxics laws

In recent years, Colorado has passed state-specific air toxics legislation to complement federal requirements. These include: 

HB21-1189: Regulate Air Toxics

HB21-1189 (Regulate Air Toxics) was signed into law in June 2021. It requires fenceline monitoring for four covered facilities, creates a community monitoring program, and ensures data is publicly accessible. Covered air toxics include hydrogen cyanide, hydrogen sulfide, and benzene. For more information:

HB22-1244: Public Protections From Toxic Air Contaminants

HB22-1244 (Public Protections From Toxic Air Contaminants) was signed into law in June 2022. It creates reporting and ambient air monitoring requirements for air toxics. Other key milestones required by the law include: 

  • The Air Quality Control Commission must adopt rules to identify up to five priority air toxics by April 2025
  • By December 2025, CDPHE will present a needs assessment for a permitting program for stationary sources of air toxics. 
  • By April 2026, CDPHE must present health-based standards for the priority air toxics to the General Assembly for consideration. 
  • By April 2026, the Air Quality Control Commission must adopt emission control regulations for new and existing stationary sources of air toxics. CDPHE will offer opportunities for public input and stakeholder engagement as part of these rulemaking processes.

For more information: 

Discover future public participation opportunities related to air toxics and air quality.

HB21-1266: Environmental Justice Act

The Environmental Justice Act was signed into law in 2021. Among several other key provisions, it directed the Air Quality Control Commission to adopt rules that must provide for enhanced modeling and monitoring requirements for new and modified sources of affected pollutants in disproportionately impacted communities. The law  identified “affected pollutants” as:

  • Volatile organic compounds
  • Nitrogen oxides
  • Fine particulate matter, and 
  • Hazardous air pollutants identified by the Commission, including benzene, toluene, ethylbenzene, and xylene. 

Discover future public participation opportunities related to air toxics and air quality.

Air pollution policies with co-benefit of air toxics reductions

Colorado has passed legislation to reduce greenhouse gasses and ozone precursor emissions such as volatile organic compounds (VOCs) and nitrogen oxides (NOx). 

While these laws and policies do not directly target air toxic emissions, a co-benefit of implementing reductions of greenhouse gasses, VOC, and NOx can often include reductions of air toxic emissions. For example, air toxic emissions have reduced 85% from electric generation, primarily coal-fired electricity generation, between 2008 and 2020 based on the 2020 EPA National Emission Inventory. Between 2005 and 2019, GHG emissions from electric generation have reduced by 26% based on the 2019 Colorado GHG Inventory Report.

Line chart showing the air toxics emissions in lb/yr since 2008 from coal, natural gas, oil, and other; coal generate the most

The data comes from the 2020 EPA National Emission Inventory isolating air toxic emissions from fuel combustion at electric generating units in Colorado. 

Colorado greenhouse gas reduction targets

Two different laws established and then accelerated GHG reduction targets in Colorado. HB19-1261 (Climate Action Plan to Reduce Air Pollution) established GHG reduction targets for the state and SB23-016 (Greenhouse Gas Emission Reduction Measures) updated these targets to achieve more accelerated reductions. 

  • The latest targets require GHG reductions of 65% by 2035, 75% by 2040, 90% by 2045, and 100% by 2050 as compared to a 2005 baseline. Review GHG emission trends on the Colorado GHG Metrics website.
  • These laws are implemented through economy-wide initiatives which are aimed at reducing consumption of more GHG-intensive fuels, transitioning to renewable resources, and improving efficiency, all of which can reduce air toxics.
  • Learn more about efforts to achieve these goals on the Air Pollution Control Division's Climate change webpage.

Colorado ozone pre-cursor emission laws and policies

The Denver Metro/North Front Range area has yet to attain the ozone national ambient air quality standards established by the U.S. Environmental Protection Agency. The Air Pollution Control Division, the Air Quality Control Commission (Commission), and the Regional Air Quality Council, along with other local partners, continue to evaluate and implement control strategies aimed at reducing emissions, particularly precursors to the formation of ozone - nitrogen oxides (NOx) and volatile organic compounds (VOCs). 

HB23-1294 (Pollution Protection Measures) updates procedures and requirements for complaint response and investigations, creates new requirements in assessing violation penalties, and creates an interim legislative committee to further study the impacts of ozone and identify potential solutions for continued improvement of ozone air quality. . 

In March 2023, Governor Polis directed CDPHE and the Colorado Oil and Gas Conservation Commission (now known as the Colorado Energy and Carbon Management Commission (ECMC)) to finalize regulations by the end of 2024 to achieve additional reductions in nitrogen oxides (NOx) from oil and gas operations during ozone season. This directive established goals of at least a 30 percent reduction of NOx during the ozone season in 2025 and a 50 percent reduction of NOx by 2030 as compared to 2017 levels. Since most NOx comes from fossil fuel combustion equipment associated with oil and gas operations, and this combustion also generates several air toxics emissions, this directive is also anticipated to achieve air toxics reductions.

Visit the Air Pollution Control Division's Ozone planning webpage to learn more about different strategies to reduce ozone pre-cursor emissions. Many of these strategies also reduce emissions of air toxics.