Since 1988, the EPA, States, and Federal land management agencies have conducted monitoring of air pollution and visibility impairment at a number of national parks and wilderness areas across the United States.

• IMPROVE Visibility Monitoring Network Exit - Access IMPROVE monitoring data resources and educational material on the science of visibility and regulations.
• Visibility Trends in Class I Areas Exit - Access summary graphs of visibility ("Visibility" under "AQRV Summaries") in Class I areas.
• Visibility Report to Congress
• National Air Quality Trends