Begin Main Content Area


Haze occurs when light is scattered by pollution particles and gases in the air. Most of these particles and gases are a result of man's activities and are from sources such as electric power generation, industrial processes, auto emissions, agricultural burning, and construction. Haze reduces the visibility in our cities and scenic areas. Even remote areas can be affected due to transport of pollutants by the wind many hundreds of miles. Visibility in Pennsylvania, without pollution, would ordinarily be 90 miles. Currently, it is only 14-24 miles. The pollutants creating haze can also be detrimental to the health of Pennsylvanians.

What is being done to reduce haze?

The U.S. Environmental Protection Agency (EPA) published the Regional Haze Rule in 1999 (64 FR 35714) with amendments finalized in 2005. (70 FR 39104.) The Regional Haze Rule calls for state and federal agencies to work together to improve visibility in 156 Class I areas. These are large national parks and wilderness areas. The rule requires states, in coordination with federal agencies and other interested parties to develop and implement air quality protection plans to reduce the pollution that causes visibility impairment.

All states, even those such as Pennsylvania that do not contain a Class I area, are required to address the contribution from sources in their state to regional haze in Class I areas that they affect. Although the goal of the regional haze rule is a return to natural visibility in the Class I areas, visibility throughout the region will improve as a result of the actions taken under this rule. The same particles that degrade visibility also have been linked to serious health effects and environmental effects such as acid rain and stream eutrophication. Therefore, actions taken to improve visibility can also be expected to benefit public health and reduce certain adverse effects to the environment.

The final Regional Haze SIP revision is available on the Bureau's State Implementation Plan web page. The Commonwealth's Regional Haze SIP revision was due to EPA by Dec. 17, 2007. Delay in the development of the SIP revision was due in part to the uncertainties caused by the D.C. Circuit Court of Appeals' 2008 remand to EPA of the Clean Air Interstate Rule. The EPA published a rulemaking notice in the Federal Register on Jan. 15, 2009, announcing a finding of failure to submit the Commonwealth's Regional Haze SIP revision (74 FR 2392). The EPA indicated that mandatory sanctions under Section 179 of the CAA will not be imposed as a result of this finding. The EPA is required to develop a Federal Implementation Plan (FIP) within two years after a finding of failure to submit a SIP revision is published in the Federal Register, if the state does not submit its SIP revision in time for the EPA to fully approve it within that time period. The EPA indicates that it may withhold a portion of the Department's air pollution grant funds provided for in Section 105 of the CAA if the FIP needs to be developed by EPA for the Commonwealth. The Regional Haze SIP revision was submitted to EPA for approval on December 21, 2010. .

The final SIP revision addresses the Regional Haze requirements, including the following: (1) the net effect on visibility resulting from changes from the 2002 base-year inventory projected by 2018 in point, area and mobile source emissions; (2) the reasonable progress goals for affected class I areas; (3) the Guidelines for Best Available Retrofit Technology (BART) Determinations for the Commonwealth's 34 BART-affected units; and (4) the Commonwealth's long-term strategy, which includes enforceable emissions limitations, compliance schedules, and other measures as necessary to achieve the reasonable progress goals. This SIP revision will demonstrate how the Commonwealth's emission control strategies, when coordinated with other state and tribes' strategies, is sufficient to meet or exceed the reasonable progress goals for affected Class I areas and improve visibility. The Regional Haze SIP revision was submitted to EPA for approval on December 21, 2010.

Federal Regional Haze Rule

The U.S. Environmental Protection Agency (EPA) published regional haze regulations in 1999 (64 FR 35714) under the authority of Section 169A of the Clean Air Act, which sets a national goal for visibility of the "prevention of any future, and the remedying of any existing, impairment in Class I areas which impairment results from manmade air pollution." The regulations were subsequently amended to provide guidelines for implementation of the Best Available Retrofit Technology (BART) requirements. (70 FR 39104 (PDF) .) The regulations require the application of BART to certain sources in 26 categories that were installed between 1962 and 1977 that have the potential to emit more than 250 tons per year of a visibility impairing pollutant. The visibility impairing pollutants addressed by the regulations are sulfur dioxide (SO2), nitrogen oxides (NOx), particulate matter (PM), and volatile organic compounds (VOC). The regulations can be found at 40 C.F.R. Part 51, subpart P (relating to protection of visibility)(PDF).

More Information

Online exchange of visibility data, research, and ideas designed to support the Regional Haze Rule enacted by the EPA to reduce regional haze in national parks and wilderness areas.

Introduction to Visibility (PDF)
Information on visibility from CIRA, Colorado State University.

Interagency Monitoring of Protected Visual Environments - Monitoring data resources and educational material on the science of visibility and regulations.

Mid-Atlantic/Northeast Visibility Union - Regional planning for improved visibility.

Live pictures and corresponding air quality conditions from scenic urban and rural vistas in the Northeast.

Regional Haze and Visibility in the Northeast and Mid-Atlantic States

EPA Information