Regional Haze

Regional Haze Four-Factor Analysis

As part of the planning process, the regional haze rule requires states to consider four statutory factors when determining which controls to consider for making reasonable progress. On December 10, 2019, the Wyoming AQD held a webinar to assist operators and sources with conducting the four-factor analyses.

A copy of the webinar presentation can be accessed in the downloader below. 

Related Programs

In 1999, the U.S. Environmental Protection Agency published a final rule to address haze causing pollution in national parks and wilderness areas (Class I Areas) in the United States.


The rule, referred to as the Regional Haze Rule, requires states, in coordination with the Environmental Protection Agency, the National Park Service, U.S. Fish and Wildlife Service, the U.S. Forest Service, and other interested parties, to develop and implement air quality protection plans to reduce the pollution that causes visibility impairment. The rule can be found in Title 40 (Protection of Environment) of the Code of Federal Regulations (CFR) §51.308. The rule was designed to meet the requirements of Sections 169A and 169B of the Clean Air Act. The EPA published a revised Regional Haze Rule on January 10, 2017 in the Federal Register that made changes to clarify or revise certain provisions of the rule and to remove provisions that were superseded.

The revised rule can be found in the Federal Register here:

Regional haze and visibility impairment will be addressed in a series of planning periods. The first planning period ended in 2018 and the second planning period began. The second planning period goes through 2028, and states must submit their State Implementation Plans (SIPs) for meeting the Regional Haze Rule requirements by July 31, 2021.

As the Wyoming Department of Environmental Quality – Air Quality Division (AQD) develops its plan for addressing regional haze, it will post material related to the regional haze planning process in this section of the AQD’s website