The government’s pollution monitoring app and website went dark for most of Monday even as toxic haze visibly thickened across the Capital—the latest unexplained breakdown in a system meant to help residents measure the pollution they can already see and feel. An update finally came late in the night, by when it crossed into its worst levels and headed for the “severe” category, above 400.
The lack of data meant that amid growing public anger, there was no way to tell how much worse – and it indeed looked worse – the air quality was from the 370 recorded on Sunday according to Central Pollution Control Board’s AQI bulletin. It also meant that most of the day, there was no estimate of how many of the city’s 39 pollution monitoring stations were in the severe (AQI 400-plus) category – a day prior, this number was 24.
The Sameer app remained frozen at 345 through the day. When it finally updated around 10pm, it showed 391—matching Sunday morning’s peak. Two hours later: 398, the season’s worst reading yet and within two points of the “severe” category, confirming what residents had seen and felt through the afternoon hours when monitors went silent. The CPCB also uploaded its daily bulletin at around 11pm, which showed an AQI of 362 — reflective of what the AQI was at 4pm.
HT attempted to access the raw source data of the key pollutants that go into calculating the AQI. The number of stations reporting PM2.5 and PM10—the year’s most prominent pollutants—dropped sharply from the 34-37 range through the morning to 27 in the hour ending noon. Then, after 12pm, data from all stations went to zero for all eight pollutants, except for a single hour when one station reported.
{{/usCountry}}HT attempted to access the raw source data of the key pollutants that go into calculating the AQI. The number of stations reporting PM2.5 and PM10—the year’s most prominent pollutants—dropped sharply from the 34-37 range through the morning to 27 in the hour ending noon. Then, after 12pm, data from all stations went to zero for all eight pollutants, except for a single hour when one station reported.
{{/usCountry}}The data blackout coincided with the afternoon hours when the haze visibly thickened and residents across the Capital reported worsening conditions. One proxy HT used was visibility at the airport, as reported by the METAR updates shared with aviators: visibility at Delhi airport dropped from 3,000 metres on Sunday between 3.30pm and 5.30pm to 1,500 metres on Monday during the same hours.
The persistent haze through daylight hours indicated pollutants were accumulating rather than fog, experts said.
CPCB officials did not respond to requests for a comment on the missing data.
The 24 stations that did provide consistent data until noon painted a grim picture of what the afternoon likely held. Their readings showed the PM2.5 sub-index—which measures fine particulate matter that penetrates deep into lungs—remained above 400, in the “severe” category, every hour from 5am through noon on Monday, peaking above 436 around 7am.
Using CPCB’s own methodology, HT calculated Delhi’s 24-hour average AQI at 362 for the period ending 4pm Monday. But that figure almost certainly understates reality—it excludes the four afternoon hours when the monitoring network went silent precisely as conditions appeared to worsen.
CPCB’s methodology requires 16 hours of data for at least one of PM2.5 or PM10, and 24-hour averages for three pollutants overall, to calculate a city’s AQI.
Officials attributed the outage to server issues that affected monitoring stations nationwide. At 5.30pm, only four of India’s 562 air quality stations were transmitting data to CPCB’s website. The number climbed slowly—66 stations by 6.30pm, roughly half by 8pm—but Delhi’s bulletin remained unpublished past 9pm.
“This was not limited to Delhi but stations across the country,” said an official aware of the situation, adding that while monitoring stations were functional, problems arose in relaying data.
A Commission for Air Quality Management (CAQM) official said the commission had directed CPCB to resolve the data transmission problems urgently. “We issued directions to CPCB to fix any issues they were facing when it comes to sharing data,” the official said.
Yet even as the monitoring breakdown unfolded, the CAQM released a statement highlighting its vigilance. “CAQM continues to closely monitor the overall air quality scenario in Delhi-NCR and remains in constant coordination with concerned agencies... to sustain the improvement trend,” the statement said.
The commission did not invoke Stage 3 restrictions despite visible conditions. “CAQM is regularly reviewing sector-specific actions and compliance,” the statement added, without addressing how such reviews proceed when data is unavailable.
On Sunday, the police detained 60-80 people at India Gate who had gathered to protest worsening air quality without permission. The demonstration followed Sunday morning’s AQI reading of 391 at 10 am—the season’s worst—and hours of deteriorating conditions that prompted the Commission for Air Quality Management to hold an emergency review — though the panel did not invoke harsher measures.
The irony was not lost on environmental analysts.
Vimlendu Jha, an environmental activist and part of the group of protestors at India Gate detained by the Delhi Police on Sunday, said it was sheer brazenness on part of the authorities to not only fail to acknowledge the air pollution but to make data go missing. “This is leading to frustration when something as fundamental as air quality data is going missing — at a time when the air quality is clearly very bad. We know Grap is a band-aid solution, but to even invoke stage 3 and 4, we need data. It is sheer arrogance from authorities, who are not willing to accept their mistakes and be transparent,” Jha said, stating even after air quality stations were found being sprinkled with water, the state government continued doing the same - in broad daylight. “This is why people are protesting,” he said.
“Even with data missing, the situation is terrible. Visibly, it is a highly polluted day,” said Sunil Dahiya, founder and lead analyst at Envirocatalysts. “Without timely data, we cannot take prompt action, including invoking Grap. Missing data only creates more confusion.”
It was the third extended data outage during pollution surges this season. On October 26, updates stopped for 11 hours between noon and 11 pm, delaying the national bulletin from its scheduled 4 pm release to 10:45 pm. The next day brought another 12-hour blackout before CPCB declared the problem resolved.