The graphic on this page shows a summary of visibility trends at IMPROVE stations across the United States. Each row of cells represents up to 26 years of trends in visibility at the indicated station. If enough data is available to calculate a trend, the cell for that year is shaded to indicate an increasing, decreasing, or stable trend.

Hover over a cell to show trend information for the available period of record up to that year. Click any trend cell to explore trends at that station.

Trends are computed following the Forest Service protocols: starting with the average deciview for the 20 percent most impaired days for each year, we compute 5-year moving averages of these for each year, fit a trend line using the Theil-Sen estimator method, and determine significance of that trend using a t-test.

Visibility trends are available for wilderness areas managed by the Forest Service, Bureau of Land Management, National Park Service, and Fish and Wildlife Service.