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

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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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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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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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

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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

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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:

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