How is acid deposition different from acid rain?

The terms are often used interchangeably, but they are not identical. "Acid rain" is a popular, informal expression, while "acid deposition" is the more accurate scientific term used to describe the various ways acidity moves from the atmosphere to the Earth's surface.12

The primary difference lies in the scope of the terms:

• Acid Rain: Specifically refers to precipitation in the form of rain that has increased acidity due to environmental pollutants.3
• Acid Deposition: A broader category that encompasses acid rain as well as other forms of "wet deposition," such as snow, sleet, hail, and fog (or cloud water). Furthermore, it includes "dry deposition," which consists of acidic particles and gases that settle on landscapes during periods without any precipitation.12

Because acid deposition includes these dry and non-rain wet forms, it is capable of affecting ecosystems and landscapes even when it is not raining. Both phenomena are primarily driven by human activities, such as the burning of fossil fuels, which release sulfur dioxide and nitrogen oxides into the atmosphere.12