Nearly a day after air quality readings went missing from several monitoring stations in the national capital on Diwali night, the Delhi Pollution Control Committee (DPCC) on Monday released the missing data, revealing that concentrations of fine particulate matter (PM2.5) had soared to 3,744 micrograms per cubic metre (µg/m³) at one of the locations.
The readings, released around 8 pm, showed that PM2.5 concentrations at several monitoring stations had crossed 2,000 µg/m³ in the early hours of Monday, exceeding the national 24-hour standard of 60 µg/m³ by more than 60 times at the worst-affected location.
Mundka recorded the highest concentration of 3,744 µg/m³ at 2 am, followed by Jawaharlal Nehru University (JNU), which registered 3,023 µg/m³ at 4 am. The NSUT West Campus station recorded 3,008 µg/m³ at 5 am. Mandir Marg, Nehru Nagar and Wazirpur were among the other locations where concentrations exceeded 2,000 µg/m³.
11 DPCC monitoring stations recorded PM2.5 concentrations above 2,000 µg/m³. All 125 station-hour readings missing from the Central Pollution Control Board's (CPCB) records were above 1,000 µg/m³ in the DPCC data. The highest reading available in the CPCB records for the night was 1,000 µg/m³.
The release comes amid questions over the availability of pollution data during the hours when the city's air quality deteriorated sharply following Diwali celebrations.
More than 20 monitoring stations were not reporting data between midnight and 2 am during peak smog hours, according to an analysis by the Centre for Research on Energy and Clean Air (CREA).
Data from Delhi's 59 air quality monitoring stations showed that the number of stations with missing readings rose sharply as Diwali night progressed, peaking in the early hours of Monday.
While only one station had missing data at 7 pm on Sunday, the number rose to seven by 10 pm and 23 by 11 pm. By midnight, 29 stations were not reporting readings, with the number rising further to 36 at 1 am on Monday. This meant that only 23 of the city's 59 monitoring stations were reporting data at that time.
The number remained high at 2 am, when 35 stations had missing data, before gradually declining. At 3 am, 30 stations were not reporting readings, while the number fell to 20 by 4 am, 19 by 5 am and 16 by 6 am.
The situation gradually improved through the morning, with 13 stations reporting missing data at 7 am and seven at 8 am. By 9 am, only two stations were not reporting readings, while one continued to have missing data until 11 am.
The missing readings were particularly significant as pollution levels were at their highest during the intervening night of Sunday and Monday.
A government official, meanwhile, told the Hindustan Times that the monitors were providing hourly data and that there had been some technical glitches. "There were some technical glitches, but all our 43 stations are giving data," the official said.
The controversy over the missing readings has triggered a political confrontation between the Aam Aadmi Party (AAP) and the BJP.
AAP president Saurabh Bharadwaj accused the BJP-led Delhi government of manipulating pollution data and alleged that several monitoring stations had been shut down during the period of peak pollution.
"The government's data is based on fraud. We showed how monitoring stations were shut down, and how 20 new AQI stations were installed in remote, lush green areas of Delhi. Water is being sprinkled directly over the monitoring stations in polluted spots to manipulate the readings," he told ANI, urging residents not to trust the official figures.
The BJP, in turn, accused the AAP of orchestrating a conspiracy to keep pollution levels high in Delhi during Diwali by encouraging stubble burning in Punjab, where the party is in power.
Delhi Minister Kapil Mishra cited around 1,200 stubble-burning incidents reported in Punjab on Sunday. His remarks came amid reports of more than 3,000 such incidents in the State between September 15 and November 6.
The release of the missing readings has brought the scale of the Diwali-night pollution spike into sharper focus, even as questions remain over the gaps in the official monitoring records and their impact on the assessment of the capital's air quality.