Emission of Pollutants:
- Industries, power plants, and vehicles emit pollutants like sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere during the combustion of fossil fuels.
- SO2 is primarily emitted from industrial activities such as metal smelting, power generation, and petroleum refining, while NOx comes from burning fuels in vehicles and power plants.
Formation of Acidic Compounds:
- In the atmosphere, SO2 and NOx undergo chemical reactions with hydroxyl radicals (OH) and oxygen (O2) to form sulfur trioxide (SO3) and nitrogen dioxide (NO2), respectively.
- SO3 and NO2 further react with water vapor (H2O) to form sulfuric acid (H2SO4) and nitric acid (HNO3). These acids dissolve in rainwater and produce acid rain.
Chemical Changes in Clouds:
- Acidic compounds such as H2SO4 and HNO3 condense and form tiny droplets that constitute clouds.
- The dissolved acids make these clouds more acidic, altering their chemical composition and pH.
Acidic Precipitation:
- When these acidic clouds encounter conditions that lead to precipitation, such as rain, snow, fog, or sleet, the dissolved acids are released into the environment.
- The resulting precipitation becomes "acid rain" or "acid deposition," characterized by a pH below the normal range found in natural rainfall.
Acid rain contains harmful levels of sulfuric and nitric acids that can have far-reaching environmental consequences. It adversely affects aquatic ecosystems, causing damage to fish populations and hindering plant growth. It also deteriorates buildings, bridges, monuments, and cultural heritage sites made of limestone or marble, causing corrosion and structural weakening.
