Excessive concentration of foreign particles or substances into the air which adversely affects the atmosphere is known as air pollution.
Sources of Air Pollution
Automobile Pollution
- Vehicular emissions form more than 80% of the total air pollution.
- Carbon dioxide, carbon monoxide, nitrogen monoxide, and unburnt hydrocarbons are some major air pollutants.
- Metropolitan cities in India such as Delhi, Kolkata, and Mumbai suffer from acute air pollution.
- Air pollution is also caused by gaseous and volatile hydrocarbons such as methane, acetylene, and ethylene. A hydrocarbon like ethylene forms petrochemical oxidants when it comes into contact with sunlight and nitrogen oxide. Petrochemical oxidants such as bad ozone are harmful to the environment.
Industrial Air Pollution
- Chemical and cement industries, cotton and paper mills, and oil refineries cause air pollution.
- Smoke emitted by these industries can cause serious health hazards as it includes dust, carbon, metals, and radioactive elements.
- The burning of coal in thermal power plants releases SO2. When SO2 combines with oxygen and water, it produces sulphuric acid. This results in acid rain.
- Industrialized cities experience high air pollution because of smoke and dust emitted by factories.
- Smog is a mixture of fog, smoke, and dust particles. It is formed in areas that have a large concentration of industries.
Burning of Garbage
- When garbage and wastes are burnt, gases such as carbon dioxide, sulphur dioxide, and nitrogen oxides are formed which pollute the environment.
- The open burning of wastes also pollutes the environment.
- The burning of forests because of fires produces nitrogen dioxide in the atmosphere. It is soluble in water and forms nitric acid resulting in acid rain.
Brick Kilns
- When coal is used for burning bricks in brick kilns, huge quantities of carbon dioxide, smoke, and dust are released which pollute the atmosphere.
- The suspended dust particles in the atmosphere are known as suspended particulate matter.
- Smoke is caused either because of the incomplete burning of coal, wood, tobacco, or other harmful chemical processes.
Burning of Fuels
- Fossil fuels are mainly burnt for producing electricity. In India, coal is used in large quantities for the generation of electricity.
- As coal is burnt in the raw form, it produces gases such as carbon dioxide, hydrocarbons, nitrogen oxides, smoke, and other dangerous particles.
- Sulphur is one of the main gases which are emitted because of the burning of coal. It causes acid rain when it combines with water. Other fossil fuels such as oil and natural gas also damage our environment by producing various greenhouse gases.
Types of Air Pollutants
Three types of air pollutants are
- Natural pollutants such as pollen grains and bacteria.
- Suspended particles in air (aerosols) such as fog, fumes, haze, dust, and mist.
- Various gases such as carbon monoxide, sulphur dioxide, and hydrogen sulphide are released into the atmosphere by various industries, vehicles, and the burning of fossil fuels.
Smog is formed as a result of air pollution. Smog is an air pollutant that is a mixture of fog, smoke, and dust particles. It is formed in areas that have a large concentration of industries. Heavy automobile traffic also results in the formation of smog.
Effects of Air Pollution
There are various effects of pollution on the environment.
Effects of Air Pollution on the Environment
- The increase of gases such as carbon dioxide, methane, nitrogen dioxide, and chlorofluorocarbons traps the Earth’s heat leading to global warming.
- Global warming can have a number of effects on our environment. It may result in the melting of ice in temperate regions.
- Global warming also increases the rate of evaporation of surface water. This may result in soil erosion and the destruction of natural vegetation.
- It may also lead to flooding, erosion, and salt formation in the deltas.
Effects of Air Pollution on Human Health
- Respiratory infections and irritation in the eyes, nose and throat.
- It causes headaches, nausea, dizziness and allergic reactions.
- Air pollution may also cause chronic respiratory diseases, lung cancer, cardiovascular diseases and even damages the nerves, kidneys and liver.
Effects of Air Pollution on Plants and Animals
- Nitrogen dioxide leads to the premature falling of leaves. It also affects the growth of plants resulting in low crop yields.
- Ozone enters the leaves of plants through stomata. It then dissolves with water within the plant and reacts with other chemicals damaging the leaves. Plants weakened by ozone may become more susceptible to various diseases, pests and droughts.
- Nitrogen dioxide causes premature falling of leaves. It also suppresses the growth of plants. This reduces crop yields.
- Peroxyacetyl Nitrate damages leafy vegetables and causes premature fall and discoloration of leafy vegetables.
- Sulphur dioxide has a bleaching effect on plants. It results in the loss of chlorophyll. Many leafy vegetables become yellow because of the effect of the gas.
- Air pollution infects the leaves of plants. When these leaves are consumed by animals, they are affected by arsenic and lead poisoning. As a result of lead poisoning, animals may suffer from bronchitis and the loss of appetite.
Apart from these, air pollution may damage the painted surfaces, fabrics, and buildings. Example: Acid rain damages buildings made of marble and limestone. The Taj Mahal has faced damage because of acid rain. Sulphuric dioxide when mixed with moisture causes corrosion of metals such as steel, copper, and zinc.
Prevention of Air Pollution
At present, many cities are suffering from high levels of air pollution. The need of the hour is to make efforts to deal with it. Two methods are considered the most effective for dealing with the problem of air pollution. These are
Source Correction Methods
It is important to reduce air pollution from the source itself. In industries, this can be achieved by designing and developing schemes and processes which can minimize air pollution in the early stages.
Pollution Control Equipment
Air pollution not only contains gaseous matter but also solid particles. Many devices and equipment have been designed to prevent air pollution. While choosing a device, any industry should keep the following points in mind:
- Amount of volume of particulate matter which has to be handled.
- Chemical and physical characteristics of the particulate along with its size.
- Temperature and humidity of gaseous medium.
- Concentration of gases in particulate size.
- Pollution control devices are basically classified into two categories—devices which control particulate contamination and devices which control gaseous contamination.
Pollution Control Devices and their Functioning
Filters
Filters are used in electric power plants to separate particulate matter from gases. The device has a series of cloth bags through which the smoke passes. This helps in trapping the particulate matter in the bags.
Gravitational Settling Chamber
- A gravitational settling chamber is a rectangular chamber in which several horizontal trays are fixed.
- When the polluted gas stream enters the chamber, its velocity is kept low so that the particulates get sufficient time to settle because of gravity.
- The high-density pollutants settle at the bottom of the chamber and are then removed.
Scrubber
- A wet scrubber is a device which is used for trapping the emissions of water-soluble gases such as sulphur dioxide, nitrogen oxide and ammonia.
- In a wet scrubber, spray nozzles are fitted through which water is sprayed into the device in a way that it goes downwards.
- As polluted gases rise upwards, their particulate matter collides with water drops. Because of the gravitational force, the water drops containing particulate matter settle at the bottom and the pollutants are segregated.
Electrostatic Precipitator
- This device is used for removing fly ash after the combustion of coal or other materials.
- After the combustion of coal and other materials, polluted gas or smoke enters the electrostatic precipitator.
- The device is electronically charged. The polluted air and impurities become negatively charged as they gain electrons on their surface.
- Negatively charged dust particles are then drawn towards the positively charged electrode plates and are deposited there.
- Impurities are then dislodged by mechanical rappers and get collected at the bottom of the unit in a hopper.
- An electrostatic precipitator is a very efficient device that removes more than 99% of impurities.
Cyclone Separator
- It is a device which is used for removing impurities and particulate matter. It works in the following ways:
- Dust-laden air is made to enter the metallic cylinder at a high speed. It has a conical shape.
- As the speed of the air is high, a vortex or a whirlwind mass of the air is created.
- As a result the particulate matter falls to the bottom and the gas moves upwards.
- The particulate matter then slides down the walls of the cylinders and gets discharged from the outlet.
Also, Read Effects of Soil Pollution