Air pollution in Delhi reached extraordinary levels during Diwali celebrations, with newly released monitoring data showing PM2.5 concentrations climbing to 3,744 micrograms per cubic metre (µg/m³), more than 62 times India's national 24-hour standard of 60 µg/m³.
The Delhi Pollution Control Committee (DPCC) released the previously missing hourly readings around 8 pm on Monday, revealing the extent of pollution during the night of November 8 and the early hours of November 9.
The data emerged after questions were raised about the disappearance of particulate matter readings from several monitoring stations as pollution intensified following Diwali celebrations.
According to an analysis by Hindustan Times, the newly available figures suggest that the capital experienced substantially higher pollution than was reflected in the Central Pollution Control Board's (CPCB) publicly available records.
𝐏𝐌𝟐.𝟓 𝐫𝐞𝐚𝐝𝐢𝐧𝐠𝐬 𝐜𝐫𝐨𝐬𝐬 𝟑,𝟎𝟎𝟎
The highest PM2.5 concentration was recorded at Mundka, where pollution reached 3,744 µg/m³ at 2 am on November 9.
Jawaharlal Nehru University recorded 3,023 µg/m³ at 4 am, while NSUT's West Campus registered 3,008 µg/m³ at 5 am.
Other severely affected locations included Mandir Marg, where PM2.5 reached 2,908 µg/m³ at 3 am, and Nehru Nagar, which recorded 2,808 µg/m³ during the same hour.
Wazirpur registered 2,721 µg/m³ at 1 am.
Altogether, 11 DPCC-operated monitoring stations recorded PM2.5 concentrations exceeding 2,000 µg/m³.
The readings were significantly higher than the national 24-hour permissible concentration of 60 µg/m³, although the newly released figures represent individual hourly measurements rather than full-day averages.
PM2.5 refers to fine particulate matter measuring 2.5 micrometres or less in diameter. These particles can penetrate deep into the lungs and enter the bloodstream, posing serious health risks.
𝐌𝐢𝐬𝐬𝐢𝐧𝐠 𝐝𝐚𝐭𝐚 𝐫𝐚𝐢𝐬𝐞𝐬 𝐪𝐮𝐞𝐬𝐭𝐢𝐨𝐧𝐬
The release followed reports that numerous monitoring stations had stopped displaying PM2.5 readings during the period when pollution was rising sharply.
At 1 am on November 9, 36 of Delhi's 59 air quality monitoring stations had no PM2.5 readings in the CPCB's records.
The analysis found that 125 station-hour readings missing from the CPCB database were subsequently available on the DPCC website.
Every one of those 125 readings exceeded 1,000 µg/m³.
Interestingly, the highest PM2.5 reading visible in the CPCB's records for the night was exactly 1,000 µg/m³, even though the DPCC figures showed concentrations reaching several times that level.
Where both agencies had published readings for the same period, the figures matched.
The discrepancy raised questions about whether technical limitations in the central reporting system prevented exceptionally high pollution concentrations from appearing in publicly accessible records.
𝐎𝐟𝐟𝐢𝐜𝐢𝐚𝐥 𝐀𝐐𝐈 𝐮𝐧𝐝𝐞𝐫 𝐬𝐜𝐫𝐮𝐭𝐢𝐧𝐲
The newly released readings also raised questions about Delhi's officially reported Air Quality Index (AQI).
According to the newspaper's calculations using the CPCB's methodology, Delhi's AQI for the 24-hour period ending at 9 am on November 9 would have been approximately 384 after incorporating the released readings.
However, the CPCB had published an AQI of 370 for the same period.
Similarly, the newspaper estimated that the 4 pm AQI would have been approximately 360, compared with the officially published figure of 344.
These are independent estimates, not revised official AQI figures.
The difference is significant because Delhi's AQI categories range from good at 0–50 to severe at 401–500.
A higher AQI indicates greater pollution exposure and associated health risks.
The AQI scale also has an upper limit of 500, meaning extremely high hourly pollutant concentrations do not translate proportionately into higher index values.
Consequently, concentrations reaching several thousand micrograms per cubic metre cannot be fully represented by the AQI scale.
𝐎𝐟𝐟𝐢𝐜𝐢𝐚𝐥 𝐜𝐢𝐭𝐞𝐬 𝐭𝐞𝐜𝐡𝐧𝐢𝐜𝐚𝐥 𝐠𝐥𝐢𝐭𝐜𝐡𝐞𝐬
A government official, speaking on condition of anonymity, attributed the missing readings to technical glitches.
The official maintained that air quality monitors had continued generating hourly readings and that all 43 DPCC-operated stations were providing data.
However, the figures remained provisional, and the released readings had not appeared in the CPCB's publicly accessible records as of 7.58 pm on Monday.
The episode has highlighted the importance of reliable pollution monitoring, particularly during episodes of exceptionally poor air quality when residents depend on official readings to assess health risks.
The discrepancy between the previously available records and the subsequently released measurements has also brought renewed attention to the limitations of reporting systems during extreme pollution events.
With Delhi already experiencing deteriorating winter air quality, the exceptionally high Diwali-night concentrations have reinforced concerns about public exposure to hazardous particulate pollution and the need for accurate, timely environmental information.