NCERT Solutions
Class 11 Chemistry
Environmental Chemistry

Q.2
Explain tropospheric pollution in 100 words.
Tropospheric pollution occurs due to the presence of undesirable solid or gaseous particles in the air.
The following are the major gaseous and particulate pollutants present in the troposphere:
1. Gaseous air pollutants: These are oxides of sulphur, nitrogen and carbon, hydrogen sulphide, hydrocarbons, ozone and other oxidants.
Oxides of sulphur (SO2 and SO3) and nitrogen (NO2, NO) are produced as a result of burning of fossil fuels (coal, automobile fuel). These oxides react with water in the presence of atmospheric oxygen to form nitric acid (HNO3) and sulphuric acid (H2SO4), which leads to the formation of ‘Acid rain’.
2SO2 (g) + O2 (g) +2H2O (l) -> 2H2SO4 (aq)
4NO2 (g) + O2 (g) +2H2O (l) à 4HNO3 (aq)
Acid rain causes harm to agriculture, plants, and trees. It also leads to various respiratory ailments.
Hydrocarbons are composed of hydrogen and carbon only and are formed by incomplete combustion of fuel used in automobiles. Hydrocarbons are carcinogenic, i.e., they cause cancer. They harm plants by causing ageing, breakdown of tissues and shedding of leaves, flowers and twigs. Carbon monoxide (CO) is poisonous in nature as it reacts with the haemoglobin of blood, which can even result in death.
2. Particulate pollutants: These are dust, mist, fumes, smoke, smog etc.
They are likely to block the nasal passage of a person, causing respiratory ailments. Smoke and fog combine to produce smog during a cool, humid day, thereby reducing visibility to a large extent. Photochemical smog is formed due to the presence of PAN, ozone, formaldehyde, and acrolein. It causes eye irritation, headaches, and chest pain. It also leads to the cracking of rubber and does damage to plants.