National Air Quality Index

The National Air Quality Index (NAQI) is a comprehensive system developed to measure, classify, and communicate the quality of air in India in a uniform and easily understandable manner. Introduced by the Government of India in 2014, the index serves as a vital tool for assessing the levels of air pollution and its potential impact on public health. It was launched under the ‘Swachh Bharat Abhiyan’ by the Ministry of Environment, Forest and Climate Change (MoEFCC) and implemented by the Central Pollution Control Board (CPCB) in collaboration with State Pollution Control Boards.

Background and Purpose

Prior to the introduction of the National Air Quality Index, air quality in India was monitored through various regional systems, each with its own parameters and reporting methods. This created inconsistencies in data interpretation and public communication. Recognising the need for a uniform national framework, the MoEFCC and CPCB developed the NAQI to provide real-time information on air quality that is both scientifically robust and easily accessible to the public.
The main purpose of the NAQI is to simplify complex air quality data into a single number, colour, and description that indicate the level of pollution and its associated health impacts. It helps citizens, policymakers, and researchers to understand and respond to air quality issues effectively.

Development and Implementation

The National Air Quality Index was formulated based on the recommendations of an expert group under the guidance of the CPCB. The index was officially launched on 17 October 2014 by the Prime Minister of India.
Initially, the system was implemented in 10 major cities, including Delhi, Ahmedabad, Bengaluru, Chennai, Lucknow, and Hyderabad. Over the years, the coverage has expanded to include hundreds of cities under the National Air Quality Monitoring Programme (NAMP).
The air quality data are collected from continuous ambient air quality monitoring stations (CAAQMS) located across the country. These stations provide hourly readings of pollutant concentrations, which are processed to generate daily Air Quality Index values.

Parameters of the National Air Quality Index

The NAQI measures air pollution based on eight pollutants that have significant effects on human health and the environment:

1. Particulate Matter (PM10) – particles with a diameter less than 10 microns.
2. Particulate Matter (PM2.5) – fine particles with a diameter less than 2.5 microns.
3. Nitrogen Dioxide (NO₂)
4. Sulphur Dioxide (SO₂)
5. Carbon Monoxide (CO)
6. Ozone (O₃)
7. Ammonia (NH₃)
8. Lead (Pb)

Each pollutant is assigned a sub-index based on its concentration and health impact, following predefined breakpoints. The overall Air Quality Index value is determined by the worst sub-index among all pollutants.

AQI Categories and Health Implications

The National Air Quality Index classifies air quality into six categories, each represented by a specific colour code and associated health advisory:

This colour-coded categorisation allows for quick public understanding and helps authorities in issuing health advisories and implementing control measures.

Calculation Methodology

The Air Quality Index is computed using a standardised formula prescribed by the CPCB. The steps involve:

1. Measurement of Pollutant Concentration: Continuous or manual monitoring data are collected for all eight pollutants.
2. Conversion to Sub-Indices: Each pollutant’s concentration is converted into a sub-index using health-based breakpoints.
3. Determination of Overall AQI: The highest sub-index value among all pollutants becomes the overall AQI for that location.

This approach ensures that even if one pollutant is at a critical level, the overall air quality reflects the associated health risk.

Implementation Mechanism

The Central Pollution Control Board (CPCB) oversees the implementation of the National Air Quality Index through a network of monitoring stations operated by State Pollution Control Boards and local authorities. Data are transmitted in real-time to CPCB’s central servers, where they are processed and displayed through multiple platforms, including:

• National Air Quality Portal (https://app.cpcbccr.com/AQI_India/)
• Mobile applications providing real-time AQI information.
• LED display boards installed in public spaces, airports, and government buildings.

The AQI information is updated on an hourly and daily basis for public awareness.

Importance and Benefits

The National Air Quality Index provides multiple benefits to policymakers, researchers, and the general public:

• Public Awareness: It informs citizens about air quality levels and the associated health risks.
• Policy and Planning: Helps authorities identify pollution hotspots and design targeted air pollution control strategies.
• Health Protection: Enables individuals to take preventive measures, particularly those belonging to vulnerable groups such as children, the elderly, and people with respiratory illnesses.
• Data Transparency: Promotes open access to environmental data, encouraging accountability and public participation.
• Performance Evaluation: Assists government agencies in evaluating the effectiveness of pollution control programmes.

Limitations of the National Air Quality Index

Despite its usefulness, the NAQI has certain limitations:

• Limited Coverage: Monitoring stations are concentrated in urban areas, leaving rural and semi-urban regions underrepresented.
• Data Gaps: Equipment malfunction or power issues can cause intermittent data loss.
• Local Variability: Air quality can vary significantly within short distances, which a single monitoring station may not capture.
• Exclusion of Certain Pollutants: Pollutants such as volatile organic compounds (VOCs) and black carbon are not currently included in the index.

Initiatives Linked with NAQI

Several government initiatives have been launched alongside the National Air Quality Index to improve air quality and strengthen pollution monitoring:

• National Clean Air Programme (NCAP) – A comprehensive action plan launched in 2019 to reduce particulate pollution by 20–30% by 2024 (later extended to 2026).
• Graded Response Action Plan (GRAP) – Implemented in the National Capital Region to control pollution based on AQI levels.
• Smart Cities Mission Integration – Many smart cities now use AQI data for urban planning and pollution management.
• Public Health Advisories – Issued regularly based on AQI readings to guide citizens’ daily activities.