Was Delhi pollution data during Diwali misleading?

One example of a station with several hours of missing data was at RK Puram in south Delhi, where 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.

But 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.

The missing data across the city means 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 in London, warned 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 told BBC Verify "for transparency", Delhi's pollution reporting could show two scenarios including and 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," Dr Clark added.

Pollution in Delhi is not limited to PM2.5 and satellite imagery shows a thick haze over the city on 8 and 9 November.