Chemical gas emissions such as sulphur and nitrogen due to any human activities are the primary contributors to acid rain.

1. Use of coal or burning of fossil fuels for electrical power generation
2. Automobiles and factories release high scores of gaseous emissions
3. Oil refineries and manufacturing industries increase the atmospheric concentration of sulphur and nitrogen gases.

These gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds such as sulphuric acid, ammonium nitrate, and nitric acid. As a result, these areas experience exceedingly high amounts of acid rain.

Go through the detailed information on Acid Rain in the given link.

Further Readings – 

1. Air Pollutants – Classification, Sources and Impacts
2. Rainfall Distribution in India
3. Montreal Protocol
4. Greenhouse Gas