Air Pollution

Air Pollution

This article deals with ‘Air Pollution – UPSC.’ This is part of our series on ‘Environment’ which is an important pillar of the GS-3 syllabus. For more articles on Science and technology, you can click here


  • Air pollution is the introduction of harmful materials into the atmosphere, which can cause undesirable changes in the atmosphere.
  • The adverse effects of the pollution include
    1. Respiratory issues for humans and animals
    2. Acid rain by elevated levels of Sulphur and Nitrogen oxides
    3. Ozone layer depletion
    4. Global warming by elevated levels of CO2 (industries, deforestation, and partial combustion)
  • According to WHO report, Air pollution caused the deaths of around 70 lakh people worldwide that year.

Air Pollutants

Substances present in the air that can adversely affect humans and the ecosystem are known as Air Pollutants.

Sources of Air Pollution

The primary sources of air pollution are:

1. Transport Sources

  • Cars, buses, aeroplanes, trucks, trains etc.

2. Stationary Sources

  • Power plants, factories, oil refineries etc.

3. Area Sources

  • Agricultural – wood, stubble burning and fertilizers.
  • Cities – vehicular pollution, industrial pollution etc. 

4. Natural Sources

  • Wind-blown dust, wildfires, lightning, volcanoes etc. 
Air Pollution

Primary vs. Secondary Pollutants

Primary Pollutants

  • Primary pollutants are emitted into the atmosphere directly through processes such as burning fossil fuel, volcanic eruptions etc. 
  • These include Sulphur Oxides, Nitrous Oxides, Carbon Monoxide etc. 

1. Sulphur Dioxide

  • Sulphur Dioxide is produced in volcanic and industrial processes. 
  • Coal and petroleum have high sulphur content, and their combustion generates sulphur oxide. Although Indian coal has low sulphur content, still this is a significant danger because of its enormous consumption. 
  • Why is Sulphur Dioxide dangerous?
    1. Oxidation of SO2  in the presence of a catalyst such as NO2 forms H2SO4 and thus causing acid rain.
    1. It is the main reason behind smog formation, and its continued exposure can result in respiratory diseases, including bronchoconstriction and asthma.

2. Nitrous Oxide

  • Nitrous Oxide is a toxic gas that is brown coloured and has a nasty odour. 
  • Sources of Nitrous Oxide include 
    1. High-temperature combustion
    2. During thunderstorms by electric discharge
  • In cities, the brown haze dome is due to Nitrogen oxide.
  • It is dangerous as it is the primary cause of Photochemical Smog, and it can cause severe respiratory problems, including intense attacks on people with asthma and old age. 

3. Carbon Monoxide (CO)

  • Carbon Monoxide is a highly poisonous gas. It becomes more dangerous because it is colourless, odourless & non-irritating.    
  • Carbon Monoxide is formed in the incomplete combustion of natural gas and coal. Vehicle exhaust is the primary source of Carbon Monoxide.
  • Carbon Monoxide in the atmosphere interferes with Oxygen transport in the body. Haemoglobin has a higher affinity with Carbon Monoxide. Hence, even a low concentration of Carbon Monoxide inhibits the bonding of oxygen with Haemoglobin, thus causing death due to suffocation.

4. Carbon Dioxide

  • Carbon Dioxide is associated with the Green House effect, ocean acidification & is emitted from combustion, factories & respiration of living organisms.

5. VOCs & NMVOCs

5.1 Volatile Organic Compounds

  • The most important VOC is Methane.
  • VOCs are Green House Gases & cause global warming.

5.2 Non-Methane VOC

  • Non-Methane VOCs are aromatic compounds such as Benzene, Toluene, Xylene & other dangerous compounds like 1,3 Butadiene.
  • They have carcinogenic properties.

6. Particulate Matters 

  • Particulate matters are microscopic solid particles lying in suspension form in a gas or liquid.
  • They are of two types, i.e. PM2.5 and PM10
  • Their major sources include the combustion of fossil fuels, fly ash produced in thermal power plants, forest fires, asbestos mining units, cement factories.
  • Repeated exposure to particulates can cause them to accumulate in the lungs & interfere with the ability of the lungs to exchange gases.

7. Fly Ash

  • Fly ash is formed as a by-product of the process of burning pulverized coal in power generation plants. It is the solidified form of coal impurities released from the combustion chamber during combustion. 
  • It has a high percentage of silica and toxic heavy metals such as arsenic.
  • It can cause the following issues 
    1. Groundwater contamination
    2. Respiratory problems
    3. Accumulation on leaves, thus reducing the efficiency of trees.

8. Chloro Fluoro Carbons (CFCs)

  • CFCs are released mainly from air-conditioning systems and refrigeration.
  • CFCs are extremely dangerous for the ozone layer. 

9. Ammonia (NH3)

  • Ammonia is emitted exclusively by agricultural sources, including livestock production and nitrogen fertilizers. 
  • Ammonia contributes to several environmental problems, including direct toxic effects on vegetation and eutrophication and acidification of sensitive ecosystems.

Secondary Pollutants

  • Secondary pollutants are not directly emitted into the atmosphere. They are formed when they react with themselves or other components of the atmosphere. 
  • These include Ground Level Ozone, Smog, POPs etc.

1. Smog 

  • Smog can result in asthma breathing difficulties.
  • Apart from humans, it also negatively impacts the health of plants and animals. 
  • There are two types of smog, and they impact the environment in different ways. These include 

1.1 Sulphurous Smog

  • Sulphurous Smog is also known as London Smog.
  • Sulphurous smog is formed by the use of Sulphur containing fossil fuels, particularly coal.
Sulphurous Smog
  • It is formed in the cool and humid climate.
  • It is chemically reducing and hence known as Reducing Smog.
  • It is characterized by blue colored skies or blue haze.

1.2 Photochemical Smog

  • Photochemical Smog occurs in the warm, dry & sunny climate.
Photochemical Smog
  • It is chemically Oxidizing and hence called Oxidizing Smog.
  • Ozone, PAN (Peroxyacetyl Nitrate), Acrolein & Formaldehyde are produced in it that can cause serious health problems.

2. Ground Level Ozone

  • It is also known as Tropospheric Ozone (The ozone layer is in the Stratosphere).
  • Ozone occurs in two layers, the stratospheric layer and in the tropospheric layer. While ozone in Stratosphere is essential for the survival of human beings, tropospheric ozone is considered a bad Ozone.
  • It is the most important secondary air pollutant.
  • New research has found that Air Purifiers emit (Tropospheric) Ozone gas.

Problems caused by Tropospheric Ozone

  • It can cause various health problems, including chest pain, bronchitis, asthma etc.     
  • Repeated exposure may permanently scar lung tissues.  
  • It also damages vegetation and the ecosystem. 
  • It leads to reduced agricultural and commercial forests yield.

3. Peroxyacetyl Nitrate (PAN)

  • PAN is present in the photochemical smog. 
  • It can decompose into phenoxyethanol radicals and nitrogen dioxide gas, causing eye irritation.

Major Disasters around the world due to Air Pollution

1. Bhopal Disaster

  • Bhopal Disaster happened in 1984.
  • Cause: Due to leakage of Methyl Iso-Cyanate (MIC) Gas.
  • Twenty-five thousand people were killed outrightly & 1.5 to 6 lakh people were exposed.

2. Great Smog of 1952

  • The Great Smog happened in London in 1952.
  • Great smog was formed due to cold weather combined with anticyclonic & windless conditions that accumulated the air pollutants from burning the coal and forming a thick layer of smog over the city.
  • In 6 days, more than 4,000 people died & 8,000 died within a month.

3. Sverdlovsk, Russia 1972

  • There was accidental leakage of Anthrax spores from the biological warfare lab, resulting in the death of many. 

Impacts of Air Pollution

Air pollution negatively impacts all organisms, depending on the atmosphere for respiration. It can result in irritation in the throat, nose, lungs, and eyes at the individual level. It results in breathing problems and asthma. In addition, polluted air reduces the body’s immunity and decreases the body’s capacity to fight other infections in the respiratory system.

1. Health impacts

Air pollutants cause a variety of health impacts. For example

  1. Sulphur Dioxide, Nitrous Oxide and Ozone: Acute respiratory problems 
  2. Carbon Monoxide: Headache, dizziness and even death due to prolonged exposure. 
  3. Ammonia: Lung fibrosis, dermatitis, cataract and glaucoma.
  4. Particulate Matter: Aggravated Asthma and Chronic Bronchitis.

2. Impact on animals

  • Air pollution also impacts the fauna. 
  • Animals are impacted in the following ways 
    1. Excessive UV radiation may cause skin cancer in wildlife.
    2. Affect animals through plants on which they feed. 

3. Impact on plants and vegetation

  • Physical injury to leaves. E.g., Ozone produces a speckle of brown spots and Ammonia results in drying out of tissues. 
  • It impacts cell metabolism and results in reduced growth.
  • Particulate matters affect the plant and trees as they block the leaf stomata through which gas exchange takes place for photosynthesis and respiration.

4. Acid Rain

  • Acid rain is the precipitation with a higher concentration of hydrogen ions. 
  • The pH of pure water is 7.0, but even in unpolluted air, there is the presence of some carbon monoxide which dissolves in raindrops to produce rain with a pH of about 5.6. Hence, in normal conditions too, rainfall is quite acidic with a pH of around 5.6. But in some parts of the world, pH as low as 1.5 is observed, resulting in Acid rain. 

5. Global Warming

  • Pollutants like Carbon Dioxide, Methane, Nitrous Oxide etc., show the Green House Gas (GHG) Effect and thus cause Global Warming. 

6. Ozone Depletion

  • Introduction of pollutants like Chloro Fluoro Carbons (CFCs) in the atmosphere results in the depletion of the Ozone layer. 
  • Ozone depletion is a serious issue as the Ozone layer protects the earth and its inhabitants from harmful UV rays in solar radiation. UV rays can cause skin cancer and impact the ecosystem negatively.

Topic: Steps taken by Government to control Air Pollution

1. National Air Quality Index (NAQI)

  • The National Air Quality Index is a number to indicate the level of pollution in the given area. 
  • It is part of Swatch Bharat Abhiyan Operational since 2014. 
  • Earlier, Government agencies used to publish air-quality data with technical terms like PM2.5, PM10. But it cant be understood by the common person. Hence, the government came up with a New Air Quality Index that uses colour-codes that even a common person can easily understand.  
  • It has 8 gases and 6 colour codes. 

6 colour codes are

National Air Quality Index

8 pollutants monitored are

PM10 Coarse Pollutants with diameters up to 10 microns.
It is emitted from dust and smoke. 
It creates breathing difficulty, particularly among asthma patients and the elderly.
PM2.5 Respirable pollutants with a diameter up to 2.5 microns.  
These are dangerous because they can go deep in the lungs and cause chronic bronchitis, lung cancer and heart disease.
NO2 Nitrogen dioxide is a lung irritant. 
It also causes red haze in traffic.
SO2 Sulphur dioxide can cause respiratory diseases like asthma, bronchitis, emphysema etc. 
CO Carbon Monoxide binds with haemoglobin and can cause death due to suffocation.
O3 Tropospheric ozone can damage the lungs.
NH3 Ammonia (NH3) in water leads to eutrophication, algal blooms, and the death of aquatic ecosystems.
Pb Lead interferes with the functioning of red blood cells.

Sameer App

  • Sameer App made by Central Pollution Control Board provides hourly updates on pollution levels on the National Air Quality Index.

Criticism of NAQI

  • One index for all: There is just one index for the entire India. But there is a need for separate indexes for residential and industrial areas & cities, and villages because pollutants found in these places differ. E.g., Methane is a significant pollutant in villages, but it is not among the gasses under observation
  • Benzene not included: Benzene is a carcinogenic chemical produced during the combustion of fossil fuels. Even European countries and the USA monitors its level. But it is not observed under NAQI. 
  • No Standard Response when dangerous levels reached mentioned: Mere informing the citizens through a colour-coded chart is insufficient. There is a need to include standard responses. For example, if the air quality index reaches a red level in China, they shut down primary schools (Note: Delhi has Graded Response, but the rest of the cities don’t have any standard response mechanism). 

2. Bharat Emission Standards

What are Bharat Emission Standards?

  • Bharat Emission norms are the pollution standards of vehicles in India. All the vehicles sold in India have to comply with these pollution standards for sale in India. 
  • They are the Indian version of Euro norms applicable in Europe. 

Difference between Bharat Norms & Euro Norms

  • Both are the same in terms of stringency/emission limits
  • India uses Euro Standards with only one modification, i.e. lower maximum speed of 90 km/hr, whereas in Euro norms, it is 120Km/hr. 


1981 Air (Prevention &Control of Pollution) Act enacted.
1991 Vehicle emission norms introduced in India.
1999 MC Mehta vs Union of India case
The Supreme Court observed that Delhi was experiencing a considerable spurt in air pollution.
Supreme Court ordered the government to introduce Euro like pollution control regime.
2000 onwards Bharat Stage Emission Standard introduced.
2003 The government of India appointed Mashelkar Committee to formulate Auto Fuel Policy. 
The Committee gave the timeline for introducing Bharat Stage (BS) Norms II and III in India.
2014 Saumitra Chaudhry recommended introducing BS-IV from 2017, BS-V from 2022 and BS-VI from 2024.
2016 The government announced that it would implement BS-VI norms by 2020 (completely bypassing BS-V). 
2017 After the Smog incident, the Government of India brought forward the date for the rollout of BS-VI for Delhi to 1 April 2018 (from 2020).
2018 BS-VI launched in Delhi
April 2020 BS-VI launched in the whole of India

Bharat Stage Norms in India

Bharat Emission Standards

BS VI: Concept and Challenges


In Bharat Stage 6, two new components have been added

  1. DPF (Diesel Particulate Filter) (actually, DPF is Stage-5 addition)
  2. SCR (Selective Catalytic Reduction) (SCR is Stage-6 addition)

But since India jumped to Stage-6 from Stage-4, Indian companies have to add these two components simultaneously. 


  1. It will make vehicles more expensive (because of the costly technology and taxes that depend on the bonnet length).
  2. Moving directly to BS-VI will require significant technological upgrades. This would leave them with insufficient time to design changes in their vehicles, considering that two critical components — diesel particulate filter (DPF) and selective catalytic reduction (SCR) module — would have to be introduced. 
  3. Oil refineries will need to upgrade petrol and diesel quality to meet cleaner fuel specifications.
  4. Loss of Jobs & service problems as serviceability will become a more significant challenge requiring highly skilled professionals and technology.
  5. In India, diesel vehicles are disproportionately higher than petrol vehicles with a diesel to petrol usage ratio (4.5): 1. Hence, a mere increase in BS levels will not bring down pollution levels. 

3. Scrapping Policy

According to Transportation Ministry, more than one crore vehicles don’t have fitness certificates and are not fit to run. These vehicles have negative externalities in the form of safety risks to commuters and pollution. But vehicle owners don’t go for new vehicles because they don’t get any financial incentive for buying a new vehicle. 

Along with that, vehicle scrapping will lead to the formation of a circular economy. The steel, plastic and rare earth metals used in the vehicles can also be recycled.

Features of Scrapping Policy

  1. The registration certificate for non-commercial vehicles will be valid for 15 years. After 15 years, the vehicle will have to pass a fitness test to get re-registered for the next 5 years.
  2. The fees for re-registration has been increased by 8 to 20 times to encourage them to move towards new and environment-friendly vehicles. 
  3. Those who opt to scrap their vehicle after 15 years will get a certificate that can be redeemed for buying new vehicles along with a waiver. 
Scrapping Policy of India

4. Electric Vehicle (EV)

  • Electric vehicles are automobiles that draw their energy from rechargeable batteries
  • They can be classified into top two types
    • Battery Electric Vehicles (BEVs): Completely relying on battery power 
    • Hybrid Electric Vehicles (HEVs): Uses battery power as well as petrol or diesel. 
  • Currently, the market share of electric cars is less than 1% in India, compared to 2% in China and nearly 40% in Norway.

Current status in India

The majority of vehicles in India still use combustion engines. The market share of electric vehicles in India is around 1% compared to world leaders like Norway, where 40% of vehicles are electric.

India should encourage Electric Vehicles because

  • Climate Friendly: The transport sector is the second-largest contributor to GHG emissions. Hence, electric vehicles will help in constraining the GHG emissions of India.
  • Saving Foreign Currency and containing CAD: It will help India contain its Current Account Deficit and foreign currency reserves by reducing the oil imports.
  • Job Creation: It can also help in job creation as India can become the hub of electric vehicle manufacturing. 

Steps taken by India to promote Electric Vehicles

1. FAME or Faster Adoption & Manufacturing of Electric vehicles

It is the main scheme of the Government of India to promote the manufacturing of Electric Vehicles in India. The main provisions of the scheme include 

  • Demand incentive in the form of reduced prices to public transport and commercial four-wheeler vehicles and private two-wheeler vehicles.
  • Setting up charging stations to ensure at least one charging station within 3 km in urban areas and within 25 km on highways

2. Taxation Measures

  • Lower GST: The GST on electric vehicles is just 5%. 
  • Income Tax Deductions: The EMI paid for electric vehicles is counted in the additional income tax deductions. 

3. State-specific measures

Various states are taking their own measures to promote electric vehicles in India. E.g.,

  • Delhi: Delhi government has announced its Electric Vehicle Policy to achieve the target of 25% of newly registered vehicles to be electric till 2024 by providing low-interest loans, incentives to scrap old petrol and diesel vehicles to switch over to EVs, no registration fee, building charging points etc.

4. Other Vehicles

  • Green Number Plates: Transportation Ministry has announced that Electric Vehicles will have special green number plates.

Way Forward

  1. Charging Stations: In India, the biggest roadblock in the introduction of electric vehicles is the inadequate number of charging stations. The greatest emphasis should be on setting up charging stations. Government should divert more subsidies to charging stations.
  2. Secure Lithium Supply: Lithium is the most critical component in battery manufacturing. India has to secure this supply by investing in mines in Congo, Chile and Bolivia as done by China. 
  3. Investment in Charging Technologies: The government research organizations and premier institutions such as IITs should invest in developing faster charging in vehicles. 

5. Air (Protection & Control of Pollution) Act ,1981

The Parliament enacted this act to arrest deteriorating air quality.

Notable points from this Act

1. Central and State Pollution Control Boards

The act has the provision for setting up Pollution Control Boards at Central and State levels. 

Central Pollution Control Board (CPCB) Central Level
State Pollution Control Board (SPCB) State Level

2. Role of these boards

These boards have following functions


  • Advices Central Government on the matters concerning improvement of air quality
  • Plan and execute a nationwide program for prevention, control and abatement of air pollution.
  • Provide technical assistance & guidance to State Pollution Control Boards 
  • Lay down standards for quality of air. 


  • Comprehensive plan for prevention, control & abatement of air pollution & to secure execution thereof

3. Define Air Pollutant

  • The act defines Air Pollutants as ‘any solid, liquid or gaseous substance( including noise) present in the atmosphere in such concentration as may be or tend to be injurious to human beings or living creatures or plant or property or environment. 

4. Air Pollution Control Areas

  • The state government, after consultation with SPCB, can declare any area as Air Pollution Control Areas (APCA). 
  • If the state government, after consultation with SPCB, believes that the use of any fuel in APCA may cause air pollution, it may prohibit the use of such fuel. 
  • No person shall, without the consent of SPCB, establish or operate any industrial plant in an APCA. 

6. Other Steps

  • Google Maps has decided to start a feature in which the system will show the most ‘eco-friendly’ route as the default route to the user based on traffic, congestion, road inclination etc. It is part of Google’s effort to fight climate change.

1 thought on “Air Pollution”

  1. Great Article. It is one of the holistic article on air pollution i have ever read.

    Thanks for sharing this article.

    Waiting for whole series on environment to be completed.


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