An official website of the United States government.

Due to a lapse in appropriations, EPA websites will not be regularly updated. In the event of an environmental emergency imminently threatening the safety of human life or where necessary to protect certain property, the EPA website will be updated with appropriate information. Please note that all information on the EPA website may not be up to date, and transactions and inquiries submitted to the EPA website may not be processed or responded to until appropriations are enacted.

We've made some changes to If the information you are looking for is not here, you may be able to find it on the EPA Web Archive or the January 19, 2017 Web Snapshot.

Visibility and Regional Haze

Visibility and Regional Haze

One of the most basic forms of air pollution - haze - degrades visibility in many American cities and scenic areas. Haze is caused when sunlight encounters tiny pollution particles in the air, which reduce the clarity and color of what we see, especially during humid conditions. Since 1988 the federal government has been monitoring visibility in national parks and wilderness areas, for example, in the Great Smoky Mountains National Park. In 1999, EPA announced a major effort to improve air quality in national parks and wilderness areas.

Visibility in Parks and Wilderness Areas

Regulatory Actions and Guidance Documents