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Air Quality Index (AQI): Categories, Calculation, Prime Facts & UPSC Notes.

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The Air Quality Index was launched in 2014 with an outline 'One Number – One Color – One Description' for the commoner to judge the air quality within his vicinity. It has been developed by the Central Pollution Control Board (CPCB). The World Air Quality Report 2024, released by Swiss company IQAir, ranked India as the 5th most polluted country globally. 

The Air Quality Index UPSC is a topic relevant to the UPSC CSE context under General Studies Paper III. It is a basic topic for aspirants who help explain the dynamic aspect of the Air Quality Index, Its Six categories, the Calculation of the index, and tools for measuring the Air Quality Index. The Air Quality Index is a relevant topic for UPSC Civil Services because it highlights the environmental issues and their impact on public health, which are frequently discussed in the exam. Join UPSC Coaching today to boost your preparation. 

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Syllabus

General Studies Paper III

Topics for Prelims

The Air Quality Index

Topics for Mains

Environmental Pollution and Degradation, Health.

What Is the Air Quality Index

The Air Quality Index is calculated by measuring the emissions of eight major pollutants in the air: Particulate Matter (PM2.5 and PM10), Ozone (O3), Carbon Monoxide (CO), Nitrogen Dioxide (NO2), Sulphur Dioxide (SO2), Lead (Pb) and Ammonia (NH3). These readings are taken every hour. Each country has its air quality indexes based on their respective air quality standards.

  • The Air Quality Index was to help simplify the common understanding of pollution. It was launched by the central government in 2014 as part of the Swachh Bharat campaign.
  • The Air Quality Index transforms complex air quality data of various pollutants into a single number (index value), nomenclature, and color. The pollutants measured include PM 10, PM 2.5, Nitrogen Dioxide, Ozone, Carbon, etc.
  • The color-coded Air Quality Index helps the public and the government understand the condition of the air and what subsequent measures are to be taken to combat the situation based on its severity.

Six categories of Air Quality Index

  • 'Good' (0-50)
  • 'Satisfactory' (50-100)
  • 'Moderately polluted' (100-200)
  • 'Poor' (200-300)
  • 'Very Poor' (300-400)
  • 'Severe' (400-500)

Calculation of the index

  • Six or eight pollutants are in the affected air, each given a weight based on a formula. That weight depends on the kind of impact it has on human health.
  • The worst of these weights is given as composite air quality, so instead of offering six different numbers and six different colors, it throws up one color and one single number to denote the overall impact. Monitoring stations across the country assess these levels.

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Air Quality Index in India

In India, government agencies are tasked with informing the public about health hazards associated with air pollution and how to mitigate them. The National Air Quality Index was launched in New Delhi in September 2014 under the Swachh Bharat Abhiyan initiative to measure India's air quality.

The Central Pollution Control Board (CPCB) has assembled an expert group comprising medical professionals, air quality experts, academicians, advocacy groups, and SPCBs. A technical study was also awarded to IIT Kanpur. In 2014, the IIT Kanpur and the expert group proposed an Air Quality Index scheme for India.

Six cities in India – New Delhi, Kolkata, Mumbai, Pune, and Ahmedabad – have a continuous real-time monitoring system that records data.

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UPSC Civil Services Examination, Previous Year Questions (PYQs) 

 

Prelims 

 

Q. In the cities of our country, which among the following atmospheric gases are normally considered in calculating the value of the Air Quality Index? (2016)

  1. Carbon dioxide 
  2. Carbon monoxide 
  3. Nitrogen dioxide 
  4. Sulphur dioxide 
  5. Methane 
 

Select the correct answer using the code given below: 

 

(a) 1, 2 and 3 only
(b) 2, 3 and 4 only
(c) 1, 4 and 5 only
(d) 1, 2, 3, 4 and 5 

 

Ans: (b)

 

Mains

 

Q. Describe the key points of the revised Global Air Quality Guidelines (AQGs) recently released by the World Health Organisation (WHO). How are these different from its last update in 2005? What changes in India’s National Clean Air Programme are required to achieve revised standards? (2021)

Tools for Measuring Air Quality

Air quality is measured using tools like particulate matter sensors, gas analyzers, and real-time air monitoring stations. These instruments detect pollutant levels and help assess Air Quality Index for public health and environmental planning. There are several instruments used for measuring air quality, including:

  1. PCE-RCM 05
  2. PCE-RCM 8
  3. PCE-HFX 100

Read about the environment and ecosystem here.

How is the Air Quality Index Calculated?

The Air Quality Index is calculated based on the average concentration of air pollutants over a specific period. This data is obtained from an air monitor or model. The Air Quality Index increases with the rise in air pollutant emissions. For instance, a high Air Quality Index value is observed during heavy traffic or forest fires. Additionally, stagnant air due to anticyclone or temperature inversion leads to high concentrations of pollutants. This results in chemical reactions between air pollutants and hazy conditions, increasing the Air Quality Index.

World Air Quality Reports - Prime Facts

India: India is the 5th most polluted country in 2024, improving slightly from 3rd place in 2023. 

Polluted Cities: Delhi is the most polluted capital globally, with a Particulate matter (PM) 2.5 concentration of 91.6 µg/m³ (micrograms per cubic meter).

  • There are 6 of the world's 10 most polluted cities and 13 of the top 20 in India, with Byrnihat (Assam-Meghalaya border) topping the list at a PM2.5 concentration of 128.2 µg/m³.
  • Other polluted cities include Mullanpur (Punjab), Gurugram, Faridabad, Bhiwadi, and Noida. 

PM2.5 Reduction: India saw a 7% decrease in PM2.5 levels, averaging 50.6 µg/m³ in 2024, down from 54.4 µg/m³ in 2023.

  • However, this is still 10 times higher than the World Health Organization's (WHO's) recommended safe limit of 5 µg/m³. 35% of Indian cities reported PM2.5 levels exceeding this limit. 

Pollution Sources: Primary contributors include industrial pollution, vehicle emissions, and biomass burning.

  • Northern India faced extreme pollution levels, with crop stubble burning contributing to 60% of PM2.5 levels. 

Global: The most polluted countries by annual average PM2.5 levels are Chad (91.8 µg/m³), Bangladesh (78 µg/m³), Pakistan (73.7 µg/m³), and Congo (58.2 µg/m³). 

  • The report highlights that most of the global population is breathing polluted air, with only 12 countries, regions, or territories reporting PM2.5 concentrations below the WHO's recommended limit.

Know more about the atmosphere and its composition here.

Particulate Matter (PM): A Major Pollutant

PM 2.5 and PM 10 are the most common methods of measuring air quality. They measure particles in micrograms per cubic meter. PM comprises a mixture of solid particles and liquid droplets in the air. Some particles, such as dust, smoke, and soot, are visible to the naked eye, while many others can only be seen under an electron microscope. Pollutants emitted by power plants, industries, automobiles, etc., undergo complex chemical reactions in the air to produce particulate matter.

Categories of the Air Quality Index

The National Air Quality Index has established six Air Quality Index categories: Good, Satisfactory, Moderately polluted, Poor, Very Poor, and Severe. Each category corresponds to specific health impacts, as shown in the table below:

AQI

Category

Health Impacts

0-50

Good/ Safe

Minimal Impact

51-100

Satisfactory

Minor breathing discomfort may be experienced by sensitive individuals

101-200

Moderately polluted

Discomfort in breathing may be experienced by patients with lung disease, heart disease, children, and older adults

201-300

Poor

Breathing discomfort on prolonged exposure and discomfort to heart disease patients

301-400

Very poor

Prolonged exposure may lead to respiratory illness. People with lung and heart diseases are severely affected.

401-500

Severe

Healthy people may experience respiratory problems. Patients with lung or heart disease can have severe health impacts. Even during light physical activity, people may experience health impacts.

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Key Takeaways on Air Quality Index For UPSC Aspirants!

 

Scale Ranges from 0 to 500: Lower values mean cleaner air; higher values indicate more pollution and health risks.

 

Color-Coded System: Green (Good) to Maroon (Hazardous) helps people quickly assess air quality levels.

 

Health Impacts Vary: Sensitive groups (children, elderly, people with respiratory issues) are affected even at moderate AQI levels.

 

Updated Frequently: AQI is updated hourly or daily, depending on the location and data source.

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Frequently Asked Questions

The National Air Quality Quality (AQI) India was launched on 17 September 2014 in New Delhi under the Swachh Bharat Abhiyan by Environment Minister Shri Prakash Javadekar.

New Delhi, the capital of India, has the worst air quality, according to the National Air Quality Index, where the main components of air pollution are the PM 2.5 and PM 10 particles.

PM 2.5 refers to the concentration of microscopic particles less than 2.5 microns in diameter, and PM 10 refers to the concentration of particles less than 10 microns in diameter.
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