Acid deposition is the comprehensive term for acidic compounds deposited from the atmosphere to the earth. Although more commonly known as "acid rain", it can be in the form of rain, snow, fog, dry particles, or aerosols.

Sources of pollutants that transform into acidic deposition include motor vehicle emissions, industrial emissions, and various forms of agricultural activities. While chronic acidification is not a problem at present, there are episodes when the capacity of our lakes and streams to neutralize acids gets reduced. This is often measured during the onset of snowmelt and during late summer rainstorms. The dilute and sensitive aquatic systems of the higher elevations are cause for concern with any increase of air pollutants.