Delhi’s missing Diwali night data released; PM2.5 at over 60 times national standard

HT had reported earlier that PM2.5 readings at many of Delhi’s stations went blank as the air worsened on the night of November 8.

The hourly air-quality readings missing from Delhi’s official record for Diwali night were released by the Delhi Pollution Control Committee (DPCC) around 8pm on Monday. They show PM2.5, the fine particles that firecracker smoke fills the air with, at up to 3,744 micrograms per cubic metre (µg/m³), more than 60 times the national 24-hour standard of 60.

A thick layer of smog engulfs Kartavya Path near India Gate following Diwali celebrations in New Delhi, India. (Arvind Yadav/HT Photo)

The highest readings came in the small hours of November 9. Mundka recorded 3,744 µg/m³ at 2am, JNU 3,023 at 4am and NSUT’s West Campus 3,008 at 5am. Mandir Marg reached 2,908 at 3am, Nehru Nagar 2,808 at 3am and Wazirpur 2,721 at 1am. Eleven of DPCC’s stations went past 2,000.

Every one of the 125 station-hours missing from the Central Pollution Control Board’s (CPCB) records is above 1,000 µg/m³ on DPCC’s website. Where both sources have a reading, the figures match. The highest reading anywhere in CPCB’s records for the night is 1,000.

HT had reported earlier that PM2.5 readings at many of Delhi’s stations went blank as the air worsened on the night of November 8. At 1am, 36 of the city’s 59 stations had no PM2.5 reading in CPCB’s records.

Counting the released readings, CPCB’s own method of calculation puts Delhi’s air quality index (AQI) for the 24 hours to 9am on November 9 at about 384, against the 370 CPCB published, and its 4pm bulletin figure at about 360, against 344, HT estimates show. The index stops at 500 for any hour above about 420 µg/m³, so readings in the thousands add little to it.

The figures are provisional. As of CPCB’s records read at 7.58pm, the released readings had not appeared there.