September AQI in Capital Was Lowest in 5 Years, Still PM2.5 and PM10 Spiked, Pg4

Key Highlights:

• Delhi recorded an average Air Quality Index (AQI) of 102 in September, marking its lowest September average in five years.
• Despite the lower overall AQI, concentrations of PM2.5 and PM10 pollutants slightly increased compared to the previous year.
• The Commission for Air Quality Management in National Capital Region and Adjoining Areas (CAQM) reported the improved average AQI.
• Data from the Central Pollution Control Board (CPCB) indicated that average PM10 rose from 104 µg/m³ in September 2025 to 106 µg/m³ this year, and PM2.5 increased from 35 µg/m³ to 39 µg/m³.
• The apparent contradiction is due to the AQI calculation method, which is determined by the pollutant with the highest sub-index, not an average of all pollutants.

Detailed Insights:

• Delhi's September AQI of 102 falls into the 'Moderately polluted' category, according to the National Air Quality Index (NAQI) classification.
• The AQI is a composite measure based on various pollutants, including PM2.5, PM10, nitrogen dioxide, ozone, sulphur dioxide, carbon monoxide, and ammonia.
• A sub-index is calculated for each pollutant, and the overall AQI reflects the highest sub-index value, meaning a rise in one pollutant might not change the overall AQI if another pollutant remains dominant.
• Monthly averages of nitrogen dioxide (NO2) and ozone were lower in September this year compared to September 2025, contributing to the overall lower AQI.
• The CAQM is a statutory body established in August 2021 to manage air quality in the National Capital Region and adjoining areas, replacing multiple previous bodies.
• The CPCB, a statutory organization established in 1974, is responsible for monitoring and controlling air and water pollution and advising the government.

Key Concepts Involved:

• Air Quality Index (AQI): A numerical index that converts concentrations of multiple air pollutants into a single measure of air quality, launched in India in October 2014.
• PM2.5: Fine inhalable particulate matter with a diameter of 2.5 micrometers or less, capable of penetrating deep into the lungs and bloodstream.
• PM10: Inhalable particulate matter with a diameter of 10 micrometers or less, which can enter and deposit within the respiratory tract.
• Commission for Air Quality Management (CAQM): A statutory body established in 2021 to coordinate and implement strategies for air quality improvement in the Delhi-NCR and surrounding regions.
• Central Pollution Control Board (CPCB): A statutory organization under the Ministry of Environment, Forest and Climate Change, responsible for air and water quality monitoring and setting environmental standards.
• National Air Quality Index (NAQI): The specific framework in India that classifies air quality into six categories from Good to Severe, based on eight key pollutants.