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Environmental Issues - Air Pollution | 12th Zoology : Chapter 13 : Environmental Issues

Chapter: 12th Zoology : Chapter 13 : Environmental Issues

Air Pollution

Earth is surrounded by a gaseous envelope which is called atmosphere.

Air Pollution


Earth is surrounded by a gaseous envelope which is called atmosphere. The gaseous blanket of the atmosphere acts as a thermal insulator and regulates the temperature of the earth by selectively absorbing The UV rays of solar radiation. The adverse effects of pollution include depletion of Ozone by Chlorofluorocarbons or CFCs, used as refrigerants and global warming by elevated CO2 (industries, deforestation, and partial combustion).

The alterations or changes in the composition of the earth’s atmosphere by natural or human activities (anthropogenic factors) are referred as Air Pollution. Pollutants include the abundant presence of solid, liquid or gaseous substances produced by human or natural activity. The nature and concentration of a pollutant determines the severity of detrimental effects on organisms and human health. 

Along with atmospheric factors (humidity, precipitation, wind, air currents, altitude) prevailing at a place and time, its effects can be far reaching and catastrophic.

Air pollutants can be

·                     discharge of dusts or particulate matter (PM: 2.5 ,10)

·                     discharge of gases (SO2, NO2, CO, CO2)

Carbon monoxide (CO) is produced mainly due to incomplete combustion of fossil fuels. Automobiles are major causes of CO pollution in large cities and towns Automobile exhausts, fumes from factories, emission from power plants, forest fires and burning of fire-wood contribute to CO pollution.

With rapid urbanization, major amount of carbon dioxide and sulphur dioxide (SO2) is released in the atmosphere. From automobiles, aeroplanes, power plants and other human activities that involving the burning of fossil fuels (coal, oil etc.,) CO2 is the main pollutant that is leading to global warming.

Nitrogen oxides are also major air pollutants. Fossil fuel combustion and automobiles exhausts are the source of nitrogen oxides. Sulphur dioxide and nitrogen oxides are the major causes of acid rain.

Particulate matters are tiny particles of solid matter suspended in a gas or liquid. Combustion of fossil fuels, fly ash produced in thermal power plants, forest fires, asbestos mining units, cement factories are the main sources of particulate matter pollution.


1. Sources

The main sources of air pollution are:

• Transport sources (Fig13.1) – cars, buses, airplanes, trucks, trains

• Stationary sources – power plants, incinerators, oil refineries, industrial facilities, and factories

• Area sources – agricultural - wood / stubble burning, fireplaces

• Natural sources – wind-blown dust, wildfires, volcanoes (Fig. 13.1).


2. Effects of Air Pollution

• Affects all organisms as they depend on the atmosphere for respiration.

• Causes irritation in the throat, nose, lungs and eyes. It causes breathing problems and aggravates existing health conditions such as emphysema and asthma.

• Contaminated air reduces the body’s defense mechanism and decreases the body’s capacity to fight other infections in the respiratory system.

• Frequent exposure to polluted air increases the risk of cardiovascular diseases. Breathing air that is filled with fine particulate matter can induce hardening of the arteries, triggering cardiac arrhythmia or even a heart attack.

• People who exercise outdoors can sometimes be susceptible to adverse effects of air pollution because it involves deeper and faster breathing. Hence it is advisable to walk or jog in the mornings in places with ample tree cover.

• Gas leaks can be lethal or affect the quality of air in the affected area.

• CO in the atmosphere interferes with O2 transport since haemoglopin has greater affinity for carbon monoxide. At low concentration it causes headache and blurred vision. In higher concentration, it can lead to coma and death.


3. Other notable effects of Air Pollution

Smog is a type of air pollution caused by tiny particles in the air. The word comes from a mixture of the words smoke and fog .

Today, smog generally refers to photochemical smog, which is created when sunlight reacts with nitrogen oxides and volatile organic compounds found in fossil fuel emissions from automobiles, factories, and power plants. These reactions create ground-level ozone and particulate matter, reducing visibility. Smog can make breathing more difficult, especially for people with asthma.

Smog also affects plants and animals. It damages crops as well as causes health problems in pets, farm animals and human beings. Smog has also been known to cause corrosive damage to buildings and vehicles.

Peroxyacetyl nitrate (PAN) is a secondary pollutant present in photochemical smog. It is thermally unstable and decomposes into peroxyethanol radicals and nitrogen dioxide gas causing eye irritation.

Global warming: Increase in the concentrations of greenhouse gases such as CO2, methane, nitrous oxide, CFCs, and ozone causes greenhouse effect, warming of the earth, resulting in sea level rise, submerging of islands and sea shores of various parts of the world.

Ozone depletion: Thinning of the stratospheric ozone layer is known as ozone depletion. Such depletion causes the ‘ozone hole’, resulting in poor screening of the harmful UV rays and increase in incidences of skin cancer. Some of the common agents that deplete ozone are CFCs.

Acid rain: Acid rain is a form of precipitation that contains acidic components, such as sulfuric acid or nitric acid. It damages trees, crops and harms marine animals (coral reefs) and induces corrosion.


4.  Control of Air Pollution

Certain measures help to remove pollutants, reduce their presence or prevent their entry into the atmosphere.

• Trees are the best remedy for urban particulate and gaseous pollution

• Forests act as carbon sinks and lungs of the planet

• Catalytic converters in vehicles help to reduce polluting gases drastically

• Diesel exhaust filters in automobiles cuts particulates

• Electrostatic precipitators reduce release of industrial pollutants.

• Cost effective air pollution treatment systems like indoor plants and high performance biofilters can improve indoor air quality.

The Taj Mahal, a UNESCO world heritage site, is facing deterioration and damage by industrial gases due to several industrial units around Agra. The white marble has decolorized to yellow.


5. Legal Protection

• The Air (Prevention and Control of Pollution) Act was enacted in 1981 and amended in 1987 for the prevention, control and abatement of Air pollution in India.

• Traffic Emissions Standards: The Government has decided to enforce Bharat Stage VI norms from 2020.

• The Green Bench and the National Green Tribunal (NGT) give judicial safeguard to environmental protection.


Steps taken by the Central and the State governments in India:

• Road traffic rationing, encourage public transport, carpooling.

• Increase green cover alongside roads (planting avenue trees).

• Promoting Swachh Bharat Abhiyan

• Enactment and Enforcement of stricter environmental laws

• Maintenance of air standards by proper enforcement and monitoring

• Reducing carbon emissions

• Encourage use of renewable energy

• Limiting the sale of firecrackers and developing eco-friendly crackers

• Make Environmental Impact Assessment mandatory


Air Quality Index (AQI) is a number used by government agencies o communicate to the public how polluted the air is at a given time.

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