Located along the mid-coast of Maine, Acadia National Park is downwind from large urban and industrial areas in states to the south and west. Periodically, high concentrations of air pollutants blow into the park from these areas. Acadia is considered a Class I area under the Clean Air Act, which means that the park deserves the highest level of air-quality protection. Consequently, Acadia is deeply involved in the National Park Service's comprehensive air resources management program, designed to assess air pollution impacts and protect air quality related resources. The air resources management program at Acadia includes monitoring, research, and regulatory interaction with state and federal agencies.

Since 1979, Acadia National Park's air quality monitoring program has been documenting current conditions and determining long-term trends. The core program measures levels of pollutants such as ozone, sulfur dioxide, nitrogen oxides, volatile organic compounds (VOC's), fine particulates, mercury deposition and acid precipitation; as well as visibility and meteorology. In addition, there is an ongoing effort to better understand the biological effects of selected air pollutants on park resources.

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 source 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.