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Regional Haze & Visibility Progress in Arizona

Revised On: Dec. 18th, 2025 - 11:35 am

What is Regional Haze & why are there rules about it?

Regional haze refers to air pollution that reduces visibility in scenic areas. It is caused by sunlight encountering fine particle pollution suspended in the air. These particles and their precursor gases react in the atmosphere, scattering and absorbing sunlight, which diminishes the clarity, color, and distance of what we see across large regions.1

Visibility protection was first introduced in the 1977 Clean Air Act (CAA) Amendments, when Congress established a national visibility goal: prevention of any future, and the remedying of any existing, impairment of visibility in mandatory Class I federal areas which impairment results from man-made air pollution.2

The 1990 Clean Air Act Amendments added a stronger focus on regional haze and required the U.S. Environmental Protection Agency (EPA) to establish the Grand Canyon Visibility Transport Commission (GCVTC). The GCVTC’s 1996 report provided key insights that informed the broader Regional Haze Rule (RHR), which the EPA finalized in 1999 | View Report >

The RHR requires states to develop and implement air quality protection plans to restore natural visibility conditions in 156 designated national parks and wilderness areas—referred to as Class I areas—by 2064 | View Rule >

The following provides a complete record of Arizona’s planning efforts and rulemakings related to regional haze.

Arizona’s Class 1 Areas

Long-term monitoring trends show that visibility is improving at Arizona's Class I areas. The state of Arizona has 12 Mandatory Class 1 Federal areas and 1 Tribal-Designated Non-Federal Class I area | View on Map >

  • Chiricahua National Monument Wilderness
  • Chiricahua Wilderness Area
  • Galiuro Wilderness Area
  • Grand Canyon National Park
  • Mazatzal Wilderness Area
  • Mount Baldy Wilderness Area
  • Petrified Forest National Park
  • Pine Mountain Wilderness Area
  • Saguaro Wilderness Area
  • Sierra Ancha Wilderness Area
  • Superstition Wilderness Area, and
  • Sycamore Canyon Wilderness Area
  • Yavapai-Apache Indian Reservation

Some of the particles that cause haze are emitted directly to the air, while others are formed from a mixture of gases that can be carried far from their original source. This is why haze is often seen in areas that don't have any major sources of air pollution nearby. Particulate matter (PM) and its precursor pollutants, sulfur dioxide (SO2) and nitrogen oxides (NOx), are the biggest contributors to haze and are caused by a variety of natural and human-caused sources. Natural sources can include windblown dust and soot from wildfires, while human-caused sources include emissions from motor vehicles, electric utility and industrial fuel burning, and various manufacturing operations. Essentially, more pollutants means more absorption and scattering of light, which in turn significantly impairs our ability to see. The amount and type of haze depends on:

  • Particle size
  • What the air particles are made of (composition)
  • How many particles are in the air (concentration)

These haze-forming particles do more than cloud your view. Some of the pollutants that form haze have also been linked to health problems and environmental damage. Exposure to very small particles in the air have been linked to health issues, such as increased respiratory illness and decreased lung function. In addition, particles such as nitrates and sulfates contribute to acid rain formation, which makes lakes, rivers, and streams unsuitable for some fish, and can erode buildings, vehicle paint, etc. 

To aid in the implementation of the RHR, the Interagency Monitoring of Protected Visual Environments (IMPROVE) is a cooperative measurement effort that was initiated in 1985 for extensive long term monitoring. Air samples are tested for sulfates, nitrates, carbon-containing particles, sea salt, fine soil and sand — all of which affect visibility. 

Visibility Progress in Arizona

ADEQ partners with the Environmental Protection Agency (EPA) and other Federal Land Managers (FLM), such as the National Park Service (NPS), Fish and Wildlife Service (FWS), and the United States Forest Service (USFS), to develop and implement air quality protection plans. Plans are submitted by states on an approximate 10-year cycle that analyze the emissions of haze-forming pollutants and their sources in order to develop control strategies for reducing those emissions and improving visibility. 

  • State Implementation Plan (SIP): States submit their plans to meet the requirements of the RHR, including reasonable progress analyses and long-term strategies. 
  • Long-Term Strategies: States must develop long-term strategies to address regional haze and ensure reasonable progress towards natural visibility conditions. 
  • Visibility Impairment Metric: Visibility impairment is measured in deciviews (dv), a measurement based on visible change perceptible to the human eye.
  • Uniform Rate of Progress (URP): The RHR uses a URP to track progress towards natural visibility conditions. The URP provides an unenforceable guide on how much visibility would need to improve each year in order to reach natural conditions by 2064.
  • Reasonable Progress Goals (RPG): RPGs are visibility improvement targets set by states for the 20 percent clearest and 20 percent most impaired days, also referred to as haziest days, which are compared against the URP for the end of each implementation period to gauge progress toward the national visibility goal. 
  • Best Available Retrofit Technology (BART): The RHR required certain older industrial facilities (built between 1962 and 1977) to install BART to reduce emissions of visibility-impairing pollutants. 

Arizona’s Regional Haze Updates, Plans, and Rules

ADEQ will continue to collaborate with the EPA and FLMs, to monitor visibility progress and revise the Arizona SIP as appropriate to ensure our Class I areas continue to make reasonable progress toward the national visibility goal.

  • Jan. 3, 2025 | ADEQ Comments on the EPA's Proposed Deadline Extension for the Regional Haze Third Planning Period | View Jan. 2025 Letter >
  • Sept. 9, 2025 | EPA Grant’s ADEQ Request for Reconsideration on EPA’s Proposed Action for Arizona’s Second Planning Period | View Sept. 2025 Letter > 
  • June 24, 2024 | ADEQ Comments on the EPA’s Protection of Visibility: Amendments to Requirements for State Plans Rule | View June 2024 Letter >

ADEQ’s Past Comments and Testimony webpage | Learn More >

  • 2025 Arizona Regional Haze 5-Year Progress Report on the Second Planning Period | View 2025 Report >
  • 2015 Arizona Regional Haze 5-Year Progress Report on the First Planning Period | View 2015 Report >

In the second implementation period (2018 – 2028) of the RHR, ADEQ did an evaluation of potential measures to reduce emissions from nonpoint sources in addition to point sources. ADEQ performed an emissions control analysis and evaluation of technical feasibility for nonpoint sources as required under the Federal RHR. Following the analysis, four dust mitigation measures (two for paved roads and two for nonresidential construction) were selected as being necessary to make reasonable progress towards achieving natural visibility conditions at Arizona’s Class I areas and suitable for rulemaking.

Arizona 2018 – 2028 Regional Haze SIP Revision 
Rules for Nonpoint Sources

ADEQ Final Air Quality Laws and Rules | View Page >

ADEQ Regional Haze Rules for Nonpoint Sources FAQs Webpage | View FAQs >

The first implementation period of the RHR (2008 – 2018) required state agencies to evaluate BART controls for certain stationary sources located near Class I areas. BART determinations dictated whether a source must comply with emissions limits or implement technology-based control measures to reduce pollutants that impact visibility. Arizona currently has several stationary sources subject to control requirements under BART as well as additional sources that are not subject to BART, but are subject to control measures that advance visibility progress under the RHR. 

  • 2016 | Coronado Regional Haze BART Alternative | View 2016 Doc >
  • 2015 | APS Cholla Regional Haze BART Reassessment | View 2015 Doc >
  • 2014 | AEPCO Regional Haze Better-than-BART SIP Revision | View 2014 Doc >
  • 2013 | Arizona Regional Haze SIP Revision (40 CFR § 51.308) | View 2013 Doc >
  • 2011 | Arizona Regional Haze SIP Revision (40 CFR § 51.308) | View 2011 Doc >
  • 2008 | Arizona Regional Haze SIP Revision Letter (40 CFR § 51.309) | View 2008 Doc >
  • 2004 | Arizona Regional Haze SIP Revision (40 CFR § 51.309) | View 2004 Doc >
  • 2003 | Arizona Regional Haze SIP Revision (40 CFR § 51.309) | View 2003 Doc >

Additional Resources

  • Grand Canyon National Park Webcam for Air Quality | View Webcams >
  • Protecting Our Nations treasured Vista’s Story Map | View EPA Story Map >
  • For any updates, join our email list. When selecting subscription topics, select Air Quality, proceed to the next page(s), select Other Air Quality Topics and then select Air Quality State Implementation Plans where listed | Subscribe >

1EPA: Visibility and Regional Haze | Visit Page 1 >
2Federal Visibility Law | Visit Page 2 >

 

Regional Haze Contact
Ph: 602-771-2373
Email >

Regional Haze & Visibility in Arizona > 
Regional Haze NPS FAQs >