Acid rain has its origins in fossil fuels
Acid rain is rain that is acidic. When fossil fuels that contain sulphur are combusted, their emissions include sulphur dioxide (SO2). When such combustion happens at a higher temperature, like inside the engine of a car, the combustion products also include nitrogen oxide and nitrogen dioxide (collectively called NOx). Both SO2 and NOx are also produced naturally, such as when volcanoes erupt or when lightning passes through the atmosphere, but in and around cities, their principal source is the use of fossil fuels for transport and power generation.
Once SO2 and NOx rise into the air, they react with water and oxygen molecules to produce sulphuric acid (H2SO4) and nitric acid (HNO3), both of which are corrosive. When these molecules dissolve in water droplets and the droplets precipitate, we have acid rain, acid snow, and even acid fog. The typical pH of acid rain is around 4.24.4. When acid rain flows into rivers and lakes, it can render the water inhospitable to some species; in soil, it destroys some bacteria. These effects can in turn adversely affect forests and other large ecosystems in complex ways.
To mitigate these effects, coal power plants have been able to reduce the SO, content in their atmospheric emissions by more than 90% using fluegas desulphurisation. Many governments around the world have also been working together to
Industrial emissions are a major contributor to acid rain.
minimise acid rain; an example in Asia is the Acid Deposition Monitoring Network in East Asia (EANET). science@thehindu.co.in