Oxides of non-metals undergo reaction with water and produce various types of acid. Pure air has a mixture of small amount of carbon dioxide and different oxides of oxygen. Animals also breathe out carbon dioxide in their respiration. The temperature of the spot where thunder strikes reach 3000°C. In that temperature, N2 and O2 present in air undergo reaction and produce NO. This NO gets oxidized by oxygen to become NO2. These oxides further get dissolved in the rainwater and produce some acids which come down to earth with rainwater. Thus, rain with these acids is called acid rain.
That is why we get the pH value of rainwater is 5 -6. However, some man-made reasons like carbon dioxide emitted from vehicles, Kitchens, power plants and industries mix with air which undergoes reaction with rainwater and produces carbonic acid (H2CO3). Besides these, the power plants, brick kilns etc. use coal and petroleum enriched with nitrogen and sulfur which again produce oxides of these elements. These also produce acids which come down to earth with rainwater.
Consequences of Acid Rain
in some places, the amount of acid in rain sometimes goes higher than expected. As a result, the pH of rainwater in these areas may drop down to 4 even below 4, which is acid rain. This rain results in a drop-down of pH of the soil. This has a severe harmful effect on human body, crops, and plants. The pH value of water in the water bodies also goes down and makes the situation uninhabitable for the lives therein. Fish production gets hampered. Acid rain also harms the buildings, marble architectures, metallic structures, and sculptures.
Source- NCTB Books