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Federal ozone pollution standards and Colorado nonattainment areas

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Colorado's ozone pollution challenge

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visible ozone in the sky

Ozone and air quality fact sheet

Background on Colorado’s nonattainment areas

Colorado’s air quality has improved over the past several decades. This includes ground-level ozone pollution, where concentrations have generally trended downward in the Denver metro/north Front Range area. However, the area is not in compliance with federal air quality standards for ozone pollution. To come into compliance, Colorado must submit plans to the U.S. Environmental Protection Agency. These plans show how Colorado will reduce ozone pollution in the nonattainment areas. Learn more about the history of ozone and past planning efforts in Colorado. 

2008 federal ozone standard nonattainment area

In 2022, the EPA reclassified the Denver metro/north Front Range as a “severe” nonattainment area under the 2008 ozone standard. It was downgraded from its previous classification as “serious” nonattainment. The attainment deadline for the 2008 standard is July 20, 2027, based on 2024-2026 ozone season data. 

2015 federal ozone standard nonattainment area

In June 2024, the division requested the U.S. Environmental Protection Agency to update Colorado’s classification for ozone pollution. The EPA approved the request on July 24, 2024. This update primarily impacts northern Weld County. The update reclassifies the Denver metro/northern Front Range, including northern Weld County, from a “moderate” to a “serious'' nonattainment area. The update is based on air monitoring data collected between 2021 and 2023, which showed the area would not meet the EPA’s 2015 standard for ozone pollution.
This voluntary reclassification provides administrative relief for both state and federal agencies, allowing the division to continue focusing on identifying and implementing strategies to reduce ground-level ozone pollution.

The division will continue to explore more ways to reduce ozone pollution and will further update Colorado's state implementation plan in the future. This process will include continued opportunities for public feedback.
 

Addressing ozone nonattainment

The Air Pollution Control Division, the Air Quality Control Commission, the Regional Air Quality Council, and other local partners continue to evaluate and implement control strategies aimed at reducing air pollution. In particular, this work focuses on reducing emissions of precursors to ozone formation — nitrogen oxides (NOx) and volatile organic compounds (VOCs).

These partners also continue to prioritize ozone precursor pollutant reductions using other ongoing strategies and directives, such as:

  • Advancing greenhouse gas reductions.
  • Advancing pollutant reductions that increase visibility.

Ground-level ozone pollution and health

Learn more about ground-level ozone and how it may impact your health.

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State Implementation Plans to meet federal ozone standards

Update: Read our December 2023 press release about the new State Implementation Plan and measures to reduce ozone.

 

EPA requires Colorado to draft and submit a State Implementation Plan. The plan details how the state will attain federal ozone standards.
 

The Air Quality Control Commission approved a new State Implementation Plan in December 2022 for the 2015 standard and in December 2023 for the 2008 standard.


The December 2023 plan shows the state will meet 2008 federal standards. Read the December 2023 State Implementation Plan and associated Technical Support Documents.

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Reducing ozone pollution formation from oil and gas

In December 2023, the Air Quality Control Commission adopted innovative measures to curb air pollution emissions from the oil and gas sector. These measures are in addition to Colorado's State Implementation Plan.

The oil and gas sector is a main source of nitrogen oxides. The new measures include requirements such as: 

  • Operators must reduce emissions during the summer months when ozone pollution is highest. This applies to drilling and pre-production operations in the parts of Colorado that do not meet federal ozone pollution standards. These operations include hydraulic fracturing, which is also called fracking. Colorado is one of the first states to have this kind of rule. 
  • Operators must reduce overall nitrogen oxide emissions over time. 
  • Operators must reduce emissions from stationary engines statewide. This includes engines for large equipment that operators park at oil and gas sites while they’re drilling.
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Reducing ozone pollution formation from lawn and garden equipment

In February 2024, the Air Quality Control Commission adopted a rule to reduce air pollution from gasoline-powered lawn and garden equipment. These measures are in addition to Colorado's State Implementation Plan.

The rule restricts the use of handheld and push gasoline-powered lawn and garden equipment for local, state, and federal governments only during summer months. Summer is the season when ground-level ozone pollution formation is highest.
 

For local governments, the rule applies:

  • Only in the ozone nonattainment area. 
  • Only to equipment below 10 horsepower.

For state government, the new rule applies:

  • Statewide.
  • For equipment below 25 horsepower.

The rule includes exemptions for:

  • Emergency services.
  • Public safety.
  • Wildfire mitigation.
  • Riparian/forest/grassland management (including noxious weed management).

The rule does not include restrictions on commercial use aside from government contracts or residential use. The rule does not restrict personal lawn mower use.

The use restrictions go into effect June 2025. The final rule language (Regulation 29) will be published in the public register on the commission's regulations website. More information on the rule can be found in this fact sheet.