Carbon dioxide is a gaseous air pollutant which is responsible for Greenhouse effect and Acid rain

Dr Ved Prakash Sahay

Assistant professor,

Department of Chemistry

S.P.College, Dumka (SKMU)

Carbon dioxide is a gaseous air pollutant which is responsible for

Greenhouse effect and Acid rain

Carbon dioxide is released into the atmosphere by respiration, burning of fossil fuels for energy, and by decomposition of limestone during the manufacture of cement. It is also emitted during volcanic eruptions. Carbon dioxide gas is confined to troposphere only. Normally, it forms about 0.03% by volume of the atmosphere. With the increased use of fossil fuels, a large amount of carbon dioxide gas released into the atmosphere. Deforestations and burning of fossil fuel increases the CO2 level and disturb the balance in the atmosphere. The increased amount of CO2 in the air is mainly responsible for global warming.

Global warming and Greenhouse effect about 75% of the solar energy reaching the earth is absorbed by the Earth’s surface, which increases its temperature. The rest of the heat radiates back to the atmosphere. Some of the heat is trapped by gases such as carbon dioxide, methane, ozone, chlorofluorocarbon compounds. Thus, they add to the heating of the atmosphere. This causes global warming.

Green house effect : it is the phenomenon in which earth’s atmosphere traps the heat from the sun and prevents it from escaping into the outer space. The carbon dioxide molecules trap heat as they are transparent to sunlight but not to the heat radiation. If the amount of the carbon dioxide crosses the delicate proportion of 0.03%, the natural green house balance may get disturbed. Carbon dioxide is the major contributor to global warming. Besides carbon dioxide, other green house gases are methane, water vapour, nitrous oxide, CFCs and ozone.

Acid rain : normally rain water has a pH of 5.6 due to the presence of H+ ions formed by the reaction of rain water with carbon dioxide present in the atmosphere.

H2O (l) + CO2(g) ↔ H2CO3 (aq)

H2CO3 (aq) ↔ H+(aq) + HCO3- (aq)

When the pH of the rain water drops below 5.6, it is called acid rain. Acid rain is a byproduct of a variety of human activities the emit the oxides of sulphur and nitrogen in the atmosphere. Burning of fossil fuels such as coal and oil in power stations and furnaces or petrol and diesel in motor engines produce sulphur dioxide and nitrogen oxides. SO2 and NO2 after oxidation and reaction with water and major contributors to acid rain, because polluted air usually contains particulate matter that catalyse the oxidation.

2SO2(g) + O2(g) + 2H2O(l) → 2H2SO4(aq)

4NO2(g) + O2(g) + 2H2O(l) → 4HNO3(aq)

Acid rain is harmful for agriculture, trees and plants as it dissolves and washes away nutrients needed for their growth. It causes respiratory ailments in human beings and animals.