Since 1979, Acadia National Park has had an air quality monitoring program that is designed to document current conditions and determine long-term trends. Although spectacular vistas are still common in Acadia, pollutants from upwind sources contaminate park air and degrade visibility. Monitoring data show that visibility conditions at the park have improved slightly from 1988 through 1998, but are still less than half what they should be at "natural background" levels.

Summer ozone levels occasionally exceed federal health standards. The highest ozone concentration reported in Maine was measured at Acadia (Isle au Haut) on June 15, 1988. Ozone concentrations below the federal health standard have been shown to damage sensitive park vegetation. The effects of atmospheric deposition are another major concern at the park. Acid precipitation (rain, snow, and fog) can be a major influence on lake and stream chemistry, cause nutrient enrichment in estuaries, and affect sensitive vegetation. Recent studies discovered high concentrations of mercury in several freshwater fish species sampled in park lakes.

The major souce of mercury in lakes appears to be deposition from the atmosphere, and it then concentrates in the food chain. Consumption of mercury-contaminated fish can be harmful to humans as well as to other wildlife.