Missing AQI data may have hidden Delhi's 'severe' Diwali pollution spike

This Diwali brought a shocking lapse to Delhi's pollution story: 173 hours of air quality readings vanished from across 31 monitoring stations, with 163 hours lost during peak pollution

Delhi’s average Air Quality Index (AQI) on the day after Diwali was likely in the ‘severe’ category contrary to what official figures indicate, The Times of India reported. The apparent mismatch stemmed from the failure of most air quality stations in the capital, which stopped recording data during the peak pollution hours on Diwali night and the following morning.

 

Surprisingly, only eight of the 39 stations in Delhi recorded uninterrupted hourly data in the 24 hours ending 4 pm on Tuesday, a period covering Diwali night and the subsequent morning. This data was used to calculate the city’s AQI for the day after Diwali (October 21).

 

173 hours of AQI data missing

While gaps in hourly AQI readings are not uncommon, the extent of the disruption this Diwali was unprecedented. A total of 173 hours of AQI data were missing across 31 stations, with nearly 163 hours lost during peak pollution hours. All figures are based on hourly data from the Central Pollution Control Board (CPCB) website.

 

According to CPCB’s hourly data, Delhi’s average air quality entered the ‘severe’ category (AQI of 400 and above) in the hour ending 10 pm on Diwali and remained there for 13 hours. During the first hour of ‘severe’ air, all 39 stations were functional. However, by 1 am – when the hourly average AQI peaked at 489, a level associated with ‘air emergency’ – only 19 stations were operational. By 3 am, data was available from just 12 stations, less than a third of the total.

 

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Extrapolated data shows severe pollution

Extrapolation of the missing hourly data paints a different picture. According to a Times of India analysis of hourly air quality readings, it is likely that the day’s average AQI would have crossed 380, approaching the ‘severe’ threshold. This estimate is consistent with readings from 29 stations that recorded an AQI of 500 — the highest on the scale — both before and after the outage.

Based on trends from the available readings, had most stations continued transmitting data, the number of stations averaging over 400 (‘severe’) for 24 hours would likely have increased from one to eight.

Minister says no data’s missing

 

There were several media reports highlighting the missing data on the night of October 22. However, Delhi Environment Minister Manjinder Singh Sirsa dismissed the claim, stating, “All data is available on CPCB and DPCC, there is no missing data.”

Yet, five days later, the AQI figures continued to reflect unavailable on the CPCB website. Officially, Delhi recorded an average AQI of 351 (‘very poor’) the day after Diwali, only six points higher than the previous day’s 345.

 

No official explanation for outage 

There has been no official explanation yet for the disruption. Despite the Supreme Court’s directive to use green crackers and restrict bursting times, many Delhi-NCR residents continued to celebrate Diwali with conventional fireworks late into the night.

3 in 4 Delhi-NCR residents say pollution harming health

 

A survey conducted by community platform LocalCircles among 44,000 verified residents of Delhi, Gurugram, Noida, Faridabad, and Ghaziabad found that three in four households were already feeling the effects of worsening air quality.  ALSO READ | Delhi's air quality 'poor'; minimum temperature lowest for Oct in 2 years

Survey reveals impact of pollution

The survey revealed that 42 per cent of respondents or their family members reported sore throats or coughs, while 25 per cent complained of burning eyes or headaches. Another 17 per cent said they faced breathing issues or asthma flare-ups, and an equal share reported runny noses, congestion, or anxiety.

Sales of air purifiers in Delhi and the National Capital Region (NCR) are also rising once again, with electronic retailers reporting higher footfall and more customer inquiries about air-cleaning devices.