Delhi's Diwali Pollution Data: Are Official Figures Misleading?

As fireworks illuminated Delhi's sky on 8 November, marking one of India's most celebrated festivals, monitoring stations across the capital recorded alarming levels of PM2.5, the fine particulate matter that poses severe risks to lung health and overall well-being. However, a BBC Verify investigation has uncovered significant discrepancies between two government datasets, suggesting that official air quality figures may have understated the true extent of the pollution crisis during Diwali.

Discrepancies in Official Data

The analysis compared data from the Central Pollution Control Board (CPCB) and the Delhi Pollution Control Commission (DPCC). It found that every hourly PM2.5 reading above 1,000 micrograms per cubic metre was absent from the CPCB's widely cited Air Quality Index (AQI), despite being recorded by DPCC monitors. The CPCB, whose figures are typically referenced by Indian media, explained in a statement that readings above 1,000 micrograms fall outside the calibrated range of its equipment and are thus excluded from calculations. "During extreme episodes which are occasional like Diwali firecracker bursting, this may appear as a data gap at the particular station concerned," the statement noted, adding that such hours do not contribute to the 24-hour average.

Expert Concerns

Dr Manoj Kumar, a researcher at the Centre for Research on Energy and Clean Air (CREA), warned that omitting high readings risks misrepresenting actual pollution levels and could erode public trust in official data. "Even short-term exposure to extreme levels of particulate matter can have adverse health impacts," he told BBC Verify. The World Health Organization recommends that annual average PM2.5 concentrations should not exceed 5 micrograms per cubic metre, highlighting the severity of Delhi's air quality crisis.

Analysis Reveals Stark Contrast

BBC Verify's analysis of 30 stations over 24 hours covering Diwali night found that available CPCB readings averaged 240 micrograms per cubic metre, less than half the average of 551 recorded in DPCC's data. On the night of Diwali, pollution levels soared as celebrations peaked. Three monitoring stations recorded hourly PM2.5 concentrations above 3,000 micrograms, according to DPCC data. Between 21:00 local time on 8 November and 07:00 on 9 November, 217 hourly PM2.5 observations were missing across 59 CPCB monitoring stations in Delhi. Only 16 stations reported complete data during this period, while 43 had at least one missing observation. None of the 116 readings above 1,000 micrograms from the 30 DPCC-managed stations appeared in the CPCB's published records.

This matters because stations need at least 16 hours of valid PM2.5 measurements to calculate a daily average, according to CPCB's methodology. A station with too many missing or invalid readings will not contribute to official pollution calculations. For instance, at RK Puram in south Delhi, pollution peaked at nearly 2,500 micrograms. Using hourly PM2.5 readings from this station, BBC Verify calculated an average concentration of about 945 micrograms over the 24-hour period after 17:00 on 8 November. However, similar averages of CPCB's published data for 14 of those 24 hours produced a much lower figure of 299 micrograms. The missing 10 hours also meant this data was not included in daily average calculations.

Impact on AQI Reporting

The missing data across the city meant that despite a sharp overnight rise in pollution at some monitoring stations, CPCB reported Delhi's AQI at 344 at 16:00 on 9 November, down from 376 at the same time the day before. Dr Sierra Clark, an environmental epidemiologist from City St George's, University of London, cautioned that classifying high pollution readings as missing could leave out days which "contribute the most to short-term health events, such as asthma attacks and heart attacks." She suggested that for transparency, Delhi's pollution reporting could show two scenarios: one including and one excluding extreme pollution episodes. "The latter would give a sense of typical pollution levels that are more representative of people's day-to-day experience. But it is also important to show the impact of those few days and what they contribute," she added.

Beyond PM2.5

Pollution in Delhi is not limited to PM2.5. Satellite imagery shows a thick haze over the city on 8 and 9 November. Measurements of other pollutants like nitrogen dioxide (NO2) and carbon monoxide (CO), as well as fire activity in the atmosphere, showed increases on 8 November. However, their overall average for Diwali week was not very high compared with 2024 and 2025.