Delhi recorded its most polluted Diwali in five years, but the severity of the pollution crisis may have been greater than official figures suggested, as more than half of the Capital's air quality monitoring stations stopped reporting data during peak firecracker use on Sunday night.
The widespread disruption in real-time monitoring raised questions over the reliability of the official Air Quality Index (AQI) readings, particularly as private monitoring platforms reported substantially higher pollution levels across Delhi-NCR.
According to an analysis by the Centre for Research on Energy and Clean Air (CREA), 36 of Delhi's 59 air quality monitoring stations were not reporting readings at 1 am on Monday, leaving only 23 stations operational during one of the most polluted periods of the night.
The gaps emerged as firecracker use continued beyond the Supreme Court-mandated time restrictions, worsening pollution levels across the Capital.
๐ ๐ผ๐ป๐ถ๐๐ผ๐ฟ๐ถ๐ป๐ด ๐ด๐ฎ๐ฝ๐ ๐ฟ๐ฎ๐ถ๐๐ฒ ๐ฐ๐ผ๐ป๐ฐ๐ฒ๐ฟ๐ป๐
CREA's analysis showed that the number of stations with missing readings increased sharply as Diwali night progressed.
At 7 pm on Sunday, only one monitoring station had missing data. The number increased to seven by 10 pm and 23 by 11 pm.
By midnight, 29 stations had stopped reporting readings, while the number rose to 36 at 1 am on Monday.
At 2 am, 35 stations were still not reporting data, followed by 30 at 3 am and 20 at 4 am.
The situation gradually improved during the morning, with 19 stations reporting missing readings at 5 am, 16 at 6 am and 13 at 7 am.
By 8 am, seven stations were not reporting data, while the number fell to two at 9 am. One station continued to have missing readings until 11 am.
The disruption meant that official pollution data was incomplete during the period when residents were likely to have experienced some of the highest concentrations of airborne pollutants.
๐๐ ๐ฝ๐ฒ๐ฟ๐๐ ๐พ๐๐ฒ๐๐๐ถ๐ผ๐ป ๐ฑ๐ฎ๐๐ฎ ๐ฟ๐ฒ๐น๐ถ๐ฎ๐ฏ๐ถ๐น๐ถ๐๐
Anumita Roychowdhury, executive director of the Centre for Science and Environment (CSE), questioned why the Capital's extensive monitoring network failed to provide reliable readings during the pollution emergency.
"When substantial public funds have been invested in establishing Delhi-NCR's air quality monitoring network โ the densest in the country โ backed by active operation and maintenance contracts, a data eclipse precisely during peak Diwali pollution is inexplicable," she said.
Roychowdhury stressed that real-time monitoring was essential for issuing targeted public health advisories and implementing emergency measures.
"While the severity of exposure is evident on the ground, credible official data is needed for institutional accountability, public awareness and mitigation. Losing data does not reduce the public health emergency," she added.
Responding to questions about the monitoring failures at a press conference, Delhi cabinet minister Kapil Mishra asked reporters to provide details of the non-functional stations and said he would seek action on the matter.
๐ฃ๐ฟ๐ถ๐๐ฎ๐๐ฒ ๐ฝ๐น๐ฎ๐๐ณ๐ผ๐ฟ๐บ๐ ๐๐ต๐ผ๐ ๐ต๐ถ๐ด๐ต๐ฒ๐ฟ ๐ฟ๐ฒ๐ฎ๐ฑ๐ถ๐ป๐ด๐
The monitoring gaps coincided with significant differences between official AQI readings and figures reported by private air quality platforms.
Official data showed Delhi's AQI at 370 at 8 am on Monday, while Swiss monitoring platform IQAir recorded an AQI of 245 on the US scale at 8.30 am, categorising the air as very unhealthy.
IQAir also reported a PM2.5 concentration of 170 micrograms per cubic metre, approximately 34 times the World Health Organisation's annual guideline value.
Another private platform, AQI.in, recorded an AQI of 637 on Monday morning, placing the city's air quality in the hazardous category. It also reported that Delhi's AQI had peaked at 2,283 after Diwali.
However, experts cautioned that direct comparisons between these figures could be misleading because monitoring agencies use different AQI scales, averaging periods and calculation methods.
The discrepancies nevertheless intensified scrutiny of the official monitoring network, particularly because several stations were not providing data during the most critical hours.
๐ช๐ผ๐ฟ๐๐ ๐๐ถ๐๐ฎ๐น๐ถ ๐ฎ๐ถ๐ฟ ๐ถ๐ป ๐ณ๐ถ๐๐ฒ ๐๐ฒ๐ฎ๐ฟ๐
According to official figures, Delhi recorded an average AQI of 376 on Diwali, making it the most polluted celebration in five years.
The morning after Diwali was only marginally better, with an AQI of 371 recorded at 10 am on Monday, the worst post-Diwali reading since 2021.
A thick blanket of smog and fog enveloped the Capital, reducing visibility and exposing residents to hazardous concentrations of pollutants.
By 4 pm on Monday, the city's average AQI had improved to 344, compared with 376 at the corresponding time on Diwali.
However, only 47 monitoring stations were reporting data at that hour. Of these, 40 recorded air quality in the very poor category, while seven were in the poor category.
Bawana registered the highest AQI at 396, followed by Burari at 393.
๐๐๐ฃ ๐ฎ๐น๐น๐ฒ๐ด๐ฒ๐ ๐ฑ๐ฎ๐๐ฎ ๐บ๐ฎ๐ป๐ถ๐ฝ๐๐น๐ฎ๐๐ถ๐ผ๐ป
The monitoring failures triggered a political confrontation, with senior Aam Aadmi Party (AAP) leader Saurabh Bharadwaj accusing the BJP-led Delhi government of manipulating air quality data to conceal the actual extent of pollution.
Bharadwaj alleged that monitoring stations were deliberately switched off during Diwali night and accused the government of using water sprinklers near certain stations to lower pollution readings.
"They are constantly sprinkling water near the Jahangirpuri AQI station so that the average comes down. Similarly, the government switched off AQI monitoring stations on Diwali night and committed data fraud. How do you trust such a government?" he asked.
The allegations have not been independently established.
Bharadwaj also claimed that 20 new monitoring stations had been installed in open and green areas with lower traffic and population density to reduce the city's overall average AQI.
Drawing a comparison with medical monitoring devices, he argued that inaccurate pollution readings could prevent residents from taking necessary precautions against hazardous air.
A similar controversy had emerged after Diwali last year, when the AAP alleged that several monitoring stations operated by the Central Pollution Control Board (CPCB), Delhi Pollution Control Committee (DPCC), India Meteorological Department (IMD) and Indian Institute of Tropical Meteorology (IITM) had stopped reporting data as pollution levels increased.
๐ง๐ฟ๐ฎ๐ป๐๐ฝ๐ฎ๐ฟ๐ฒ๐ป๐ฐ๐ ๐ฐ๐ฟ๐๐ฐ๐ถ๐ฎ๐น ๐ฑ๐๐ฟ๐ถ๐ป๐ด ๐ฒ๐บ๐ฒ๐ฟ๐ด๐ฒ๐ป๐ฐ๐
Radhey Shyam Sharma, head of the Department of Environmental Studies at Delhi University, said transparency in air quality monitoring was essential, particularly during severe pollution episodes.
"Transparency in data should be there. There is also the question of accountability. We are talking about an emergency situation, a severe emergency," Sharma said.
He warned that missing readings could create confusion among residents and undermine efforts to assess the actual severity of pollution.
Sharma also pointed out that private monitoring platforms do not necessarily calculate AQI using the same averaging methods as government agencies.
"The official data should clearly specify the location and time of the readings. The exposure levels need to be clear so that there is a better picture of the situation," he said.
He added that citywide average AQI figures could differ substantially from peak pollution levels, when exposure-related health risks were particularly high.
Experts maintained that the monitoring network needed stronger management and accountability to ensure uninterrupted reporting during severe pollution episodes.
The latest controversy has brought renewed attention to the reliability of Delhi's air quality monitoring system, with experts warning that incomplete data during pollution emergencies could undermine public health advisories, policy decisions and efforts to hold authorities accountable.