The Phenomenon of acid rain was first introduced by Rober Angus smith in 1852. Is means presence of excessive acids in rain water?
Acid rain is a form of precipitation (rain, snow or hail) containing high levels of sulphuric and nitric acid. It is produced when sulphur dioxide (SO2) and various nitrogen oxides (NOx) combine with atmospheric moisture and form like H2SO4 and HNO3. The Ph of normal rain water is 5.6 when ph falls below this level then it becomes acid rain.
Chemical reactions of acid rain
Generally rain water contains H2SO3, H2SO4, HNO3 and H2CO3 which are formed by following reactions.
(i) SO2 + - O2 SO3
2 root particles
SO3 + H2O H2SO4
SO2 + H20 H2SO3
(ii) NO + O3 NO2 + O2
NO2 + O3 NO3 +O2
NO3 +NO2 N2O5
N2O5 + H2O 2HNO3
(iii) CO2 + H2O H2CO3
(iv) Some HCI gas present in the atmosphere dissolves in moisture and produces
HCL (g) + H2O HCI (eq)
These Acid Droplets Are Partly Neutralized With Bases Such As Nh3 Etc.
NH3 + H+ NH+
Settling of dust particles containing sulphates and nitrate is known as dry deposition.
Uses of acid rain:
(i) Emission of industries and power plant.
(iii) Natural causes such as volcanic eruption and forest fire.
Harmful effects of acid rain
Acid rain causes extensive damage to plants, animals, human beings, natural ecosystem, buildings etc. the damages caused by acid rain are:
1. Crops and forests are damaged due to acidification of soil and alternative of seed germination eg. Decline in the population of red spruce in north east is caused by acid rain.
2. The activity of symbiotic nitrogen fixing bacteria present in nodules of leguminous family is inhibited; thereby destroying the fertility of soil.
3. In human beings it causes burning to eyes and irritation to mucous membrane.
4. It causes neurological diseases and can cause complication in respiratory system and digestive system.
5. Acid rain affects buildings and structural materials. It causes intensive damage to historical, artistic buildings or monuments. Structures made of lime stone reacts with acid as follows:
CaCO3 + H2 SO4 CaSO4 + H2O + CO2
The attack on marble is called stone leprosy. The Taj Mahal in Agra is also suffering due to SO2 and H2SO4 fumes and other pollutants released from Mathura refinery.
6. It causes corrosion to statues, bridges, fences; railing and oil based which is costing the world 1450 million dollars a year.