When a beam of sunlight enters a room, we can see thousands of tiny particles dancing around in the air. These particles cannot be the atoms and molecules of gases, comprising the air, because we cannot see these atoms and molecules. Also, the sunlight is invisible, what we see is dust. The dust particles which are solid are seen because they reflect the sunlight and make the light beam visible.
Dust is only one of the impurities in the air. Smoke, chemical fumes, plant pollens and disease germs are some of the other impurities present in the air. When the air contains harmful impurities, it is said to be polluted. An undesirable change in the physical, chemical or biological characteristics of air is called air pollution. Substances which pollute the air are called pollutants. Air pollution can endanger the health and well-being of all the people in a community.
Sources of air pollution: Pollution can either be caused by natural causes or by human activities.
Air Pollution by Natural Causes:
1. Volcanic Eruptions:
Huge amounts of gases and particulate matter is released with lava from volcanic eruptions.
2. Winds and Storms:
Strong winds and storms carry huge amounts of dust and sand with them thus polluting the air.
3. Forest Fires:
Forest fires release large amounts of smoke and ash into the air.
Marshlands produce large amounts of methane gas which pollutes the air.
Besides the above-mentioned sources, pollen grains and fog all pollute air. However, the extent of pollution produced by natural sources is very small when compared to the pollution produced by human activities.
Air Pollution by Human Activities:
1. Burning of Fuels:
Burning of fuels like wood, coal or kerosene to cook food produces thick smoke which contains carbon monoxide, sulphur dioxide and unburnt carbon.
2. Automobiles Exhaust:
Automobiles use petrol or diesel which produces large amounts of smoke, carbon monoxide, lead, nitrogen oxides and particulate matter on burning.
3. Thermal Power Plants:
Thermal power plants burn huge amounts of coal to produce electricity. They release smoke and ash into the atmosphere.
Industries emit enormous amounts of smoke and pollutants like oxides of sulphur and nitrogen, lead particles and chlorofluorocarbons (CFC) into the atmosphere.