India’s major cities woke up to varying levels of air pollution post-Diwali on November 9 morning, with Delhi recording air quality that bordered on ‘severe’ even as Chennai, Mumbai, Bengaluru and Kolkata remained in comparatively better categories.
Data from the Central Pollution Control Board (CPCB) dashboard at 6 am showed Delhi’s city-level Air Quality Index (AQI) at 366, while readings at several monitoring stations in the national capital crossed 430.
Delhi worst-affected
Delhi recorded its most polluted Diwali in five years with an average AQI of 376. The AQI at 10 am on Monday was recorded at 371 when a blanket of smog and fog blanketed the city.
The overall AQI stood at 371 at 10 am on Monday, also the highest for a post-Diwali day since 2021.
Of the 51 monitoring stations that recorded data, 14 were in the ‘severe’ category, four in the ‘poor’ category and the remaining 33 in the ‘very poor’ category. Delhi Technological University (DTU) recorded the worst reading of 439. Earlier in the morning, the overall AQI stood at 370 at 8 am.
According to CPCB data, the Diwali-day AQI of 376 was the highest recorded on the day of the festival since 2021, when it was recorded at 382.
According to the Central Pollution Control Board (CPCB), an AQI between 0 and 50 is classified as ‘good’, 51 and 100 as ‘satisfactory’, 101 and 200 as ‘moderate’, 201 and 300 as ‘poor’, 301 and 400 as ‘very poor’, and 401 and 500 as ‘severe’.
It is worth noting that Diwali falls on different days in October or November every year. It was on November 8 this year, on October 20 in 2025, October 31 in 2024, November 12 in 2023, October 24 in 2022 and November 4 in 2021.
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The high readings come amid concerns over firecracker use during Diwali. In several parts of Delhi, firecracker activity reportedly continued beyond 10 pm, the permitted time window. The resulting pollution adds to the city’s existing winter air quality challenges.
Chennai’s AQI in ‘poor’ category
Southern cities recorded relatively lower AQI readings. Chennai’s city-level AQI stood at 206, with Arumbakkam recording 243 and Manali Village 269. The readings placed the city in the ‘poor’ category. Chennai also experienced rainfall through much of Sunday, which could help disperse pollutants and improve air quality.
Mumbai recorded a city-level AQI of 170. However, some monitoring stations reported higher readings, with Deonar at 221, Bandra-Kurla Complex at 224 and Kerwadi in Bandra East at 259.
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Bengaluru recorded the lowest city-level AQI among the five cities at 124. The City Railway Station monitoring station registered 217, while Silk Board recorded 146 and Hombegowda Nagar 129.
In Kolkata, the city-level AQI stood at 169. Among individual monitoring stations, Ballygunge recorded 185, Rabindra Bharati University area 182 and Fort William 183.
Why some AQI data gives scores above 1,000
Different air quality indices use different scales, which explains why some platforms report readings exceeding 1,000 while the CPCB dashboard does not.
India’s national AQI system has a scale ranging from zero to 500. The highest category, ‘severe’, covers readings between 401 and 500. The scale is capped at 500, meaning that even when pollution levels rise further, the reported AQI does not necessarily increase beyond this limit.
Other systems, including the US Environmental Protection Agency’s AQI framework, use different calculation methods and scales. Some alternative reporting systems also provide extended or uncapped readings, which can result in scores above 1,000.
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However, a reading of 500 or 1,200 indicates extremely hazardous air quality, even though the numbers cannot be directly compared across different AQI systems.
PM2.5 pollution
A more useful way to understand the health risks is to examine the concentration of fine particulate matter, particularly PM2.5, measured in micrograms per cubic metre (µg/m³). These particles are small enough to penetrate deep into the lungs and can enter the bloodstream.
Under India’s national standards, the 24-hour permissible limit for PM2.5 is 60 µg/m³, while the World Health Organisation recommends a much lower limit of 15 µg/m³. Concentrations above these thresholds pose increasing health risks, particularly for children, older people and those with respiratory conditions.
The CPCB dashboard and the government’s SAMEER mobile application provide PM2.5 and PM10 concentration readings alongside AQI data, offering a clearer picture of the pollution burden.