At peak of air pollution on Deepavali, data goes missing at several government monitoring stations in Delhi

Air quality data from several government monitoring stations in Delhi went missing for hours during the pollution spike following Deepavali on Sunday (November 8, 2026), with experts warning that the gaps have led to understated pollution levels and resulted in a lower official air quality index (AQI).

According to Dr. D. Saha, former head of the Central Pollution Control Board (CPCB)’s air quality laboratory, AQI values are calculated using a moving or running average of hourly concentrations of eight parameters, including PM2.5 and PM10, over the previous 24 hours.

On Monday (November 9, 2026), PM2.5 data were missing for several hours at many stations in the city, including Anand Vihar, Patparganj and Bawana, on the CPCB website. PM2.5 (particulate matter measuring 2.5 micrometres or less in diameter) consists of fine inhalable particles that can penetrate the lungs and enter the bloodstream, causing respiratory and other diseases.

Similar data gaps were reported at several monitoring stations during Deepavali last year as well. Manoj Kumar, an analyst at the Centre for Research on Energy and Clean Air (CREA), a Finland-based non-profit research organisation, said the missing hourly PM2.5 data “raised concerns about the assessment of Delhi’s air quality”.

“From midnight on November 8 until 5 a.m. on November 9, 227 hourly PM2.5 observations were missing across 59 CPCB monitoring stations in Delhi. Only 14 stations reported complete data, while the remaining 45 had at least one missing hourly observation,” Mr.

Kumar said, adding, “When the hourly PM2.5 data is missing, it will artificially lower the AQI, showing better air quality when the actual air quality is worse.” When asked about the missing air quality data at several monitoring stations, Delhi Labour Minister Kapil Mishra told the media that the government would look into the issue.

The Member Secretary of the CPCB, which releases AQI data, did not respond to calls and messages seeking comment. Dr. Saha told The Hindu that there should not be gaps in the data, especially during crucial periods. “If hourly PM2.5 or PM10 value is blank or missing, it will affect the AQI calculated and the final value of the AQI calculated will be less than the actual value of AQI and scientifically incorrect,” Mr.

Saha said. He also said the CPCB had set the measurement range of PM2.5 analysers at 0–1,000 micrograms per cubic metre, which meant they could not measure concentrations above that level. “So, if the value of PM2.5 is beyond 1,000, it should at least be shown as 1,000 instead of showing blank,” he said.

A former DPCC scientist, who did not wish to be identified, said the CPCB recorded PM2.5 values only up to 1,000 micrograms per cubic metre because there was a minor drop in accuracy at higher levels. “But at very high values, a small drop in accuracy will not matter a lot.

Ideally, the CPCB should be measuring the higher values so that we are not missing the peak values,” the official said, adding that not measuring higher concentrations would artificially make air quality appear better. Bhavreen Kandhari, an environmental activist, alleged that the government was clearly fudging the data to conceal the actual air pollution situation rather than solving the problem.

On the CPCB website, PM2.5 readings appeared to be capped at 1,000 micrograms per cubic metre across all stations, with data missing for several hours at multiple locations. According to CPCB data, PM2.5 concentration in Anand Vihar spiked to 767 micrograms per cubic metre at 11 p.m.

on Sunday (November 8, 2026), about 51.13 times the World Health Organization’s (WHO) 24-hour guideline of 15 micrograms per cubic metre. However, readings were missing for the next three hours, while PM10 data were unavailable for five hours.

Similarly, PM2.5 concentration in Patparganj, east Delhi, peaked at 930 micrograms per cubic metre at 10 p.m. on Sunday (November 8, 2026), about 62 times the WHO’s guideline, before readings went missing for three hours.

CPCB data also showed that PM10 readings were missing for seven hours at the station. Mr. Kumar said Siri Fort in south Delhi recorded a PM2.5 concentration of 1,000 micrograms per cubic metre. “The portal does not display readings above this level, raising concerns about the representation of extreme pollution concentrations,” he said.