Acid Rain
Acid rain is a result of air pollution. When any type of fuel is burnt, lots of different chemicals are produced.
The smoke that comes from a fire or the fumes that come out of a car exhaust don't just contain the sooty grey particles that you can see - they also contains lots of invisible gases that can be even more harmful to our environment.
Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions (low pH).
Effects of acid rain
It can have harmful effects on plants, aquatic animals and infrastructure.
Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids.
Some Governments have made efforts since the 1970s to reduce the release of sulfur dioxide and nitrogen oxide into the atmosphere with positive results.
precipitation, as rain, snow, or sleet, containing relatively highconcentrations of acid-forming chemicals, as the pollutants from coalsmoke, chemical manufacturing and smelting, that have beenreleased into the atmosphere and combined with water vapor: harmfulto the environment.
Carbon dioxide reacts with water to form carbonic acid (Equation 1). Carbonic acid then dissociates to give the hydrogen ion (H+) and the hydrogen carbonate ion (HCO3-) (Equation 2).
The ability of H2CO3to deliver H+ is what classifies this molecule as an acid, thus lowering the pH of a solution.
CO2+H2O --->H2CO3---------(1)
H2CO3 --->H+ + HCO3------------------(2)
Nitric oxide (NO), which also contributes to the natural acidity of rainwater, is formed during lightning storms by the reaction of nitrogen and oxygen, two common atmospheric gases (Equation 3).
In air, NO is oxidized to nitrogen dioxide (NO2) (Equation 4), which in turn reacts with water to give nitric acid (HNO3) (Equation 5).
This acid dissociates in water to yield hydrogen ions and nitrate ions (NO3-) in a reaction analagous to the dissociation of carbonic acid shown in Equation 2, again lowering the pH of the solution.
N2(g) + O2--->2NO(g)-----------------(3)
NO(g) + 1/2 O2(g)--->NO2(g)----------------(4)
3NO2(g)+H2O--->2HNO3(aq)NO(g)---------------(5)
Cause of acid rain
Forms of Acid Rain
Wet Deposition:
When the wind blows the acidic chemicals in the air to the areas where the weather is wet, the acids fall to the ground in the form of rain, sleet, fog, snow or mist.
It removes acid from the atmosphere and deposit them on the earth’s surface. When this acid flows through the ground, it affects large number of plants, animals and aquatic life.
The water from drain flows into rivers and canals which is them mixed up with sea water, thereby affecting marine habitats.
Dry Deposition:
If the wind blows the acidic chemicals in the air to the areas where the weather is dry, the acidic pollutants slip into dust or smoke and fall to the ground as dry particles.
These stick to the ground and other surfaces such as cars, houses, trees and buildings. Almost 50% of the acidic pollutants in the atmosphere fall back through dry deposition. These acidic pollutants can be washed away from earth surface by rainstorms.