Two sources which cause air pollution due to SPM are as follows :
(i) Automobiles which burn diesel and petrol, produce SPMthat remain suspended in air and reduce visibility. When inhaled, they cause diseases.
(ii) Industrial activities like manufacturing of steel and mining give out SPM which also pollute the atmosphere.

Hot water released by powerplants and industries is considered a pollutant because it raises the temperature of the water body. The high temperature of water reduces its oxygen content. This adversely affects the animals and plants living in it.

Algal bloom is caused by the enrichment of nutrients in the water body. The nutrients from the fertilisers, etc cause rapid growth of algae. It affects in following ways:
(i) Deteriorate the water quality.
(ii) Lead to death of aquatic organisms

Air pollutants like sulphur dioxide and nitrogen dioxide react with the water vapour present in the atmosphere and forms sulphuric acid and nitric acid respectively. These acids drop down with rain as acid rain. Acid rain affects us in the following ways:
(i) It corrodes the marble of the monuments such as Taj Mahal.
(ii) It damages our crops and also makes them poisonous
(iii) It causes damage to aquatic life, e.g. decrease in fish population of lakes due to decreased O₂.
(iv) The low pH of acid rain water changes the rate of metabolism of organisms.

Differences between pure air and polluted air are as follows:

Nitrogen is not a greenhouse gas. It is naturally found in the air and is a major constituent of it.

Sulphur dioxide and nitrogen dioxide are the two gases mainly responsible for acid rain.

Lead and arsenic are two water pollutants which are toxic for both plants and animals.

Volcanoes and dust storms are natural sources of air pollution

X is ozone, Y is Ultraviolet (UV) rays.

Chlorofluorocarbons (CFCs) are the chemical compounds which are used in refrigerators, air conditioners and aerosol sprays, and damage ozone layer when released in air.

(a) It is recommended to stop the vehicle engine at the red light signals to minimise the emissions of poisonous gases like CO, NO, etc from the automobile exhaust.
(b) With the vehicle engine ON, the incomplete combustion of fuel will take place with release of gases like CO.
(c) The government is trying to make people understand the need for reducing environment pollution and the small steps that they can take for environmental protection.
(d) Yes, I will support the message. It is for the common good.
(e) Arjun is keen learner, strong observer and responsible.

CFCs stand for chlorofluorocarbons.
CFCs are used in refrigerators, air conditioners and aerosol sprays.
CFCs are considered as pollutants because these are depleting the useful ozone layer of the upper atmosphere.
CFCs released into the air, go up and ultimately reach high into the atmosphere where the protective ozone layer exists. The chlorofluorocarbons react with ozone gas of ozone layer and destroy it gradually. This allows the harmful ultraviolet rays of the sun to reach the earth and cause damage.