A day after Diwali, Delhi is technically breathing cleaner air, leaving residents wondering how pollution levels improved despite the festival’s firecracker emissions and a spike in stubble-burning incidents
in neighbouring Punjab.
Experts, however, have pointed to two possible factors behind the improvement: favourable wind conditions that helped disperse pollutants and missing data from a substantial number of air quality monitoring stations when pollution levels were high.
Dr Manoj Kumar, an air quality and energy analyst at the Centre for Research on Energy and Clean Air (CREA), raised concerns over missing PM2.5 readings from 36 of Delhi’s 59 monitoring stations during the early hours of November 9.
He said the absence of data from such a large number of stations could affect the city’s overall pollution averages and potentially paint a misleading picture of air quality.
“For a particular period, data from nearly 36 out of Delhi’s 59 monitoring stations went missing. That’s a substantial number. When data from so many stations is unavailable, the city’s overall average PM2.5 concentration can come down, and we may not get an accurate picture of pollution levels at that particular time.
“Missing data can also bring down the daily average concentration and, consequently, affect the AQI calculation if those readings are excluded. So, effectively, the reported pollution levels could appear lower than the actual levels,” Kumar said.
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According to Kumar, 36 monitoring stations had missing hourly PM2.5 data at 1 am on November 9, raising questions about the accuracy and representativeness of the pollution data during a critical period.
Delhi’s Air Quality Index (AQI) stood at 344 at 4:53 pm on November 9, compared with 376 on November 8, 369 on November 7 and 382 on November 6, according to the Central Pollution Control Board (CPCB) data.
However, Kumar said the improvement was not entirely attributable to missing data, pointing out that favourable meteorological conditions had also helped disperse pollutants across Delhi-NCR.
“Actually, this morning we had very good wind conditions. Better wind conditions support the dispersion of pollutants, and that’s why we had better or cleaner air, not just in Delhi but across the NCR,” he said.
He stressed that favourable winds and missing monitoring-station data were two separate issues that needed to be examined independently.
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Pollution Levels On Diwali: Delhi Records Fourth Most Polluted Day Of 2026
Despite the subsequent improvement in air quality, Diwali 2026 was the fourth most polluted day of the year in Delhi, with the daily average PM2.5 concentration reaching 257 micrograms per cubic metre (µg/m³).
The preceding days also featured among the most polluted days of the year. November 5, 6 and 7 ranked sixth, seventh and eighth, respectively, in terms of daily average PM2.5 concentrations, as per the CREA.
Diwali 2026 was also the fourth most polluted Diwali in Delhi since 2016, with a daily average PM2.5 concentration of 257 µg/m³.
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Meanwhile, Siri Fort recorded a PM2.5 concentration of 1,000 µg/m³, the maximum value displayed on the Central Pollution Control Board’s (CPCB) Central Control Room (CCR) public portal.
The portal does not display readings beyond the 1,000 µg/m³ mark, raising concerns about whether the actual intensity of extreme pollution episodes is being adequately captured and represented.
