Acid rain, or more accurately, acid precipitation, encompasses any form of precipitation containing heightened levels of hydrogen ions (low pH), primarily due to atmospheric pollutants like sulfur and nitrogen oxides. An example of acid precipitation is acidic rain itself. However, acid precipitation isn't limited to rain; it also includes:
- Acidic snow: Snowfall can carry the same acidic components as rain.
- Acidic fog: Fog can become acidic through the absorption of atmospheric pollutants.
- Acidic hail: Hailstones can incorporate acidic particles during their formation.
- Acidic dust: Even dry deposition, in the form of acidic dust particles, constitutes acid precipitation.
These forms of precipitation result from the interaction of atmospheric pollutants—primarily sulfur dioxide (SO2) and nitrogen oxides (NOx)—with water molecules in the atmosphere, forming sulfuric and nitric acids. As noted by the EPA (https://www.epa.gov/acidrain/what-acid-rain), acid deposition is a broad term encompassing all these forms. The increased acidity in these precipitation types can have significant environmental impacts, affecting water bodies, soil, and vegetation.
The Merriam-Webster dictionary defines acid precipitation as "precipitation (such as rain or snow) having increased acidity caused by environmental factors (such as atmospheric pollutants)." (https://www.merriam-webster.com/dictionary/acid+precipitation). This highlights that the acidic nature is not naturally occurring, but a result of human activities and pollution.
