New Delhi: Delhi witnessed a massive spike in air pollution following Diwali celebrations on Sunday (November 8), with PM2.5 concentrations in several parts of the national capital exceeding 66 times the World Health Organization’s (WHO) recommended 24-hour guideline, as per a report by The Hindu.The choking pollution, however, is only part of Delhi’s Diwali air nightmare. Equally disturbing are the questions surrounding the transparency of its air quality monitoring systems, after several stations stopped reporting data just as pollution levels surged. More troublingly, this is no isolated incident nor is it the first time. Similar disruptions have occurred on previous Diwali nights, as The Wire previously reported, raising serious questions about why critical pollution data repeatedly disappears when the city needs it most.Missing data: Delhi’s Diwali pollution mystery returnsIn a report, NDTV highlighted how the Delhi Pollution Control Committee’s (DPCC) website suddenly stopped displaying real-time pollution data from several monitoring stations just as pollution levels were surging on Diwali night. The affected stations included R.K. Puram, Nehru Nagar, Mundka, Sonia Vihar and Dwarka.The report stated that R.K. Puram recorded fine particulate matter (PM2.5) levels of 504 micrograms per cubic metre (µg/m³) before its data stopped appearing after 9 P.M. The concentration had reportedly reached 924 µg/m³ by then. India’s National Ambient Air Quality Standards (NAAQS) and WHO’s air quality guidelines set different permissible levels for PM2.5 levels. NAAQS prescribes a 24-hour permissible PM2.5 limit of 60µg/m³ and an annual average of 40 µg/m³. The WHO, however, has more stringent standards. It recommends that levels of PM 2.5 should be no more than 15 µg/m³ for a 24-hour period and 5 µg/m³ annually. Meanwhile, the JNU monitoring station, located in a relatively less-populated part of South Delhi, continued reporting readings. Its PM2.5 concentration increased from 161 µg/m³ at 8 P.M. to 786 µg/m³ by 11 PM.NDTV also pointed out that interruptions in online pollution data were observed last Diwali as well, with technical glitches often cited as the reason.Residents continued bursting firecrackers well beyond the 10 PM deadline set by the Supreme Court, despite restrictions allowing only green firecrackers during specified time windows on November 7 and 8.The Hindu’s report stated that data from the DPCC showed that Punjabi Bagh recorded PM2.5 concentration of 993 µg/m³ at 4 AM on Monday (November 9), approximately 66.2 times the WHO’s recommended limit of 15 µg/m³Vivek Vihar recorded 873 µg/m³ at 2 AM, while R.K. Puram registered 924 µg/m³ at 10 PM on Sunday, highlighting the extent of the pollution spike.However, these figures do not capture the full extent of Delhi’s pollution crisis. A separate analysis by Hindustan Times found that 42% of the expected hourly PM2.5 readings from 39 monitoring stations were missing between 10 p.m. and 6 a.m. on Diwali night. The newspaper also found that several stations continued reporting gaseous pollutants even as their particulate matter readings disappeared.AAP accuses Delhi government of fudging numbersThe Aam Aadmi Party (AAP) on Wednesday accused the BJP government in Delhi of deliberately shutting down air quality monitoring stations on Diwali night to conceal the actual pollution levels.In a video post on X, AAP Delhi president Saurabh Bharadwaj questioned the government’s handling of pollution data.“The government which shuts down air quality monitoring stations on the night of Diwali, the government that does data fraud, how will you trust such a government?” he asked.Bharadwaj further alleged that his party had written to the Commission for Air Quality Management (CAQM) and the Central Pollution Control Board (CPCB) over suspected manipulation but claimed that no action had been taken.Last week, AAP had also accused the Delhi government of manipulating AQI readings by allegedly spraying water on monitoring stations. The party described the alleged practice of altering pollution figures as a serious public health concern.However, concerns over the credibility of Delhi’s air quality monitoring systems have surfaced before as well. In an earlier Hindi video report, The Wire highlighted reports of monitoring stations being sprayed with water to bring down pollution readings. The report also raised questions about the placement of monitoring stations, pointing out that some were located under trees or near green belts rather than in densely populated areas like schools and residential neighbourhoods. Bharadwaj too questioned the expansion and placement of Delhi’s air quality monitoring systems, alleging that the BJP government had added stations in greener and less polluted areas to artificially bring down the city’s average AQI. Drawing a parallel with what he described as manipulation of national economic data, he said:“In the last two years, this BJP government added 20 new AQI monitoring stations at far greener and cleaner locations so that the average AQI of Delhi can be reduced mathematically. This is similar to GDP manipulation by the Central Government.”Diwali air pollution spike hits cities across IndiaThe post-Diwali pollution spike was not confined to the national capital, with several other Indian cities also reporting deteriorating air quality. In another report, The Hindu highlighted worsening conditions across the country, with Mumbai witnessing hazy skies and a thick blanket of smog over areas such as Kalanagar and Bandra.According to the report, Kherwadi-Bandra East recorded an AQI of 264, followed by Sewri at 226, Ghatkopar at 221 and Chembur at 216. Byculla recorded 193, Mindspace-Malad West 191, Kandivali West 187 and Worli 148, while Kurla registered a comparatively lower AQI of 96.In Uttar Pradesh, a thick layer of smog blanketed Lucknow, with several parts of the city waking up to hazy conditions.As per the CPCB website, as of 4:00 P.M. today, Chennai recorded an AQI of 199, followed by Amritsar (257), Nagpur (268), Indore (261), Ahmedabad (223), Kolkata (153) and Mumbai at 172. Delhi remains under ‘severe’ pollutionAs per the report by The Hindu, according to CPCB data, Delhi’s 24-hour average AQI stood at 370 at 9 A.M. on Monday, placing the city in the ‘very poor’ category. Several localities, including Chandni Chowk, ITO, Rohini, Mundka and Delhi University’s North Campus, continued recording ‘severe’ air quality.In a post on X, the official account of AQI India, a private air quality monitoring platform said, “99 out of 100 most polluted cities in the World are in India right now.” However, AQI’s readings are not directly comparable with CPCB official data, as the platform may use a different monitoring network and methodology.According to the CPCB website, as of 4:00 P.M. today, Delhi’s PM2.5 reading stood at 344 µg/m³, placing it in the ‘very poor’ category while Burari-DPCC recorded the highest concentration at 376 µg/m³.