What is Acid Rain?

Rain normally has a pH value of between pH 5 – 6. Acid rain occurs when the pH value of rain falls below pH 5. Acid rain is used to describe any form of precipitation with acidic components like sulfuric acid and nitric acid that falls to the ground as wet or dry deposition. Wet deposition refers to rain, fog, and snow, while dry depositions exist as acidic gases and particles.

How is Acid Rain Formed?

Rain is naturally acidic as atmospheric carbon dioxide (CO2) dissolves in water to form carbonic acid. Natural occurrences such as volcanic eruptions and lightning in the atmosphere contribute further to the acidity of rain.

However, human activities cause rain to become more acidic. These activities include the burning of coal in power plants, as well as emissions from car exhausts. These activities lead to the release of SO2 and NOx, which dissolve in water to produce acid rain.

A diagram showing where various substances fall on the pH scale.
Fig.1 pH scale on various substances

Why is Acid Rain Harmful?

Fig.2 Diagram of pollutant and acid deposition pathway

Acid rain contributes to the corrosion of infrastructure, damage to agricultural activities, loss of marine life and nutrients leaching.

SO2 and NOx, which are the main causes of acidic rain, can be transported over long distances by the wind, often causing trans-boundary pollution. This can lead to the formation of acid rain even in places that do not produce much of these pollutants.

How Can We as Individuals Reduce Acid Rain?

In order, to reduce the emissions of gases that cause acid rain, we could try to walk, cycle, or take public transport to reduce emissions from car exhausts.

We could also save energy by turning off appliances that are not in use or use energy saving products, to reduce our reliance on coal-powered energy sources.

Image result for clean transportation
Fig.3 A hybrid electric bus, minimizing pollutant emission.



References and Image Credits:
1) Unit 6 – Neutralizing the Threat of Acid Rain