For Prelims: Air Quality Index (AQI), PM2.5 and PM10, Central Pollution Control Board (CPCB), Total monitoring stations in Delhi, Stations with complete data on Diwali 2026, Official PM2.5 average (Diwali night 1 AM), Estimated actual peak PM2.5, Pollutant with most missing readings
For Mains: Data integrity in environmental monitoring, Limitations of AQI instruments, Transparency in pollution governance, Impact of missing data on public health response
Source:
Hindustan
5 facts for one-day exams
SSC, railway, police and teaching exams ask direct questions like these.
- Delhi has 59 air quality monitoring stations.
- On Diwali 2026, only 14 stations recorded complete data.
- The official PM2.5 average was 592 µg/m³.
- The estimated actual peak PM2.5 was 800 µg/m³.
- SO₂ had the most missing hourly readings (253).
Why in the news?
Of Delhi's 59 air quality monitoring stations, 45 had missing hourly readings for at least one pollutant during Diwali 2026. Experts warn that official data (PM2.5 average of 592 µg/m³) may understate actual pollution because missing readings often coincided with peak levels near the instrument limit of 1,000 µg/m³, with the real peak estimated at 800 µg/m³.
Summary
- Delhi has 59 air quality monitoring stations; during Diwali 2026, only 14 recorded complete data for all pollutants.
- The Lodhi Road (IITM) station had the most missing data: 96 of 192 expected hourly readings were absent.
- Sulphur dioxide (SO₂) had the most missing readings (253), followed by ammonia (NH₃, 221), PM10 (116) and PM2.5 (55).
- The official PM2.5 average at 1 AM on Diwali night was 592 µg/m³, about 10 times the 24-hour standard, but the actual peak may have been around 800 µg/m³.
Highlights
Data Gaps Mask Real Pollution
45 of 59 monitoring stations had missing hourly readings, potentially understating Delhi's Diwali air pollution.
Peak Readings Near Instrument Limit
Missing data often occurred when PM levels approached the monitor's 1,000 µg/m³ ceiling, hiding the true peak.
Official vs. Estimated Levels
While the official PM2.5 average was 592 µg/m³, experts estimate the actual peak reached about 800 µg/m³.
Background
Delhi's air quality monitoring network of 59 stations is operated by the Central Pollution Control Board (CPCB) and other agencies. During high-pollution events like Diwali, continuous hourly data is critical for accurate assessment. Missing data undermines the credibility of official AQI reports and hampers policy responses.
Key Analysis and Impact
The analysis by the Indian Express and experts from CREA reveals that data gaps were not random but correlated with peak pollution hours. Instruments reaching their upper measurement limit (1,000 µg/m³) may have failed to record further spikes. Treating these as 'missing' and averaging the rest artificially lowers the reported AQI. This has implications for public health advisories, the Graded Response Action Plan (GRAP) implementation, and public trust in official data.
Way Forward
Experts recommend that instead of discarding missing readings, a minimum value of 1,000 µg/m³ should be imputed for those periods to avoid underestimation. CPCB may need to upgrade monitoring instruments with higher measurement ranges and ensure real-time data redundancy. A transparent audit of monitoring station performance during high-pollution events is essential for accurate pollution management.
Official vs estimated PM2.5 levels on Diwali 2026
| Measure | Value |
|---|---|
| Official average (1 AM) | 592 µg/m³ |
| Estimated actual peak | ≈ 800 µg/m³ |
| Instrument measurement limit | 1,000 µg/m³ |
| 24-hour safe standard (India) | 60 µg/m³ |
Delhi connection
Matters for these Delhi exams:DSSSB 7/10
Background GK
Textbook concepts you need to understand this news
- Air Quality Index (AQI)
- A numerical index used to communicate how polluted the air currently is or how polluted it is forecast to become. It is calculated based on eight major pollutants: PM10, PM2.5, NO₂, SO₂, CO, O₃, NH₃, and Pb.
- PM2.5 and PM10
- Particulate matter (PM) with a diameter of less than 2.5 micrometres (PM2.5) and 10 micrometres (PM10). PM2.5 can penetrate deep into the lungs and enter the bloodstream, posing severe health risks.
- Central Pollution Control Board (CPCB)
- A statutory organisation under the Ministry of Environment, Forest and Climate Change (MoEFCC), established in 1974 under the Water (Prevention and Control of Pollution) Act, 1974. It coordinates pollution monitoring and enforcement across India.
Facts to remember
Tap a card to see the answer. Try to recall it first.
How exams will ask this
- Data: 59 monitoring stations in Delhi; only 14 had complete data on Diwali 2026; official PM2.5 average was 592 µg/m³; estimated peak was 800 µg/m³.
- Nodal Body: Central Pollution Control Board (CPCB) under the Ministry of Environment, Forest and Climate Change.
- Legal Point: Graded Response Action Plan (GRAP) — implemented by the Commission for Air Quality Management (CAQM) for Delhi-NCR.
Don't make this mistake!
They may ask about the 'official' PM2.5 level (592 µg/m³) vs the 'estimated actual peak' (800 µg/m³) and try to swap the two. Also, note that the 24-hour safe standard for PM2.5 is 60 µg/m³ (India) or 15 µg/m³ (WHO). The official level was 'about 10 times' the standard, so the standard implied is 60 µg/m³.
Write these in mains answers
- Data integrity in environmental monitoring, Limitations of AQI instruments, Transparency in pollution governance, Impact of missing data on public health response
Stuck? Get it in one tap
Delhi has 59 air quality monitoring stations that measure pollutants every hour. On Diwali 2026, 45 of these stations did not record complete data for all pollutants. Many readings went missing when pollution levels were very high, near the instrument's limit of 1,000 µg/m³. Because of this, the official average PM2.5 level of 592 µg/m³ may be lower than the actual peak, which experts estimate was around 800 µg/m³.
- Delhi has 59 air quality monitoring stations.
- On Diwali 2026, only 14 stations recorded complete data.
- The official PM2.5 average was 592 µg/m³.
- The estimated actual peak PM2.5 was 800 µg/m³.
- SO₂ had the most missing hourly readings (253).
- Environment: Air pollution and monitoring
- Governance: Environmental governance and regulatory bodies
Related concepts: Air Quality Index (AQI), PM2.5 and PM10, Central Pollution Control Board (CPCB)
Practice questions
Pick an answer, then read the explanation.
- Q1Easy
Which body is primarily responsible for operating air quality monitoring stations in Delhi?
Explanation: The Central Pollution Control Board (CPCB) is the statutory body under the MoEFCC that coordinates and operates the national air quality monitoring network, including stations in Delhi. The DPCC is a state-level body under CPCB. CAQM is a separate body for GRAP implementation, not for routine monitoring.
- Q2Hard
Consider the following statements regarding Delhi's air quality monitoring during Diwali 2026:
- 1.Of the 59 monitoring stations, 45 had missing data for at least one pollutant.
- 2.The pollutant with the most missing hourly readings was PM2.5.
- 3.The official PM2.5 average at 1 AM on Diwali night was 592 µg/m³.
Which of the statements given above is/are correct?
Explanation: Statement 1 is correct: 45 of 59 stations had missing data. Statement 2 is incorrect: SO₂ had the most missing readings (253), not PM2.5 (55). Statement 3 is correct: the official CPCB average was 592 µg/m³ at 1 AM on Diwali night. Hence option C is correct.
- Q3Medium
What was the estimated actual peak level of PM2.5 in Delhi on Diwali night 2026?
Explanation: Environmental expert Sunil Dahiya estimated that the actual peak PM2.5 level may have reached about 800 µg/m³. 592 µg/m³ was the official recorded average. 1,000 µg/m³ is the instrument's measurement limit. 253 is the number of missing SO₂ readings, not a pollution level.
- Q4Medium
What is the primary concern raised by experts regarding the missing data from monitoring stations?
Explanation: Experts noted that missing readings often coincided with peak pollution hours near the instrument limit of 1,000 µg/m³. Averaging the remaining data without imputing a minimum value for those periods leads to an understated AQI. There is no evidence of deliberate removal, station shutdown, or cyber attack.
Frequently asked questions
1. How many air quality monitoring stations are there in Delhi?
There are 59 air quality monitoring stations in Delhi, operated by the Central Pollution Control Board and other agencies.
2. How many stations had complete data on Diwali 2026?
Only 14 of the 59 stations recorded complete hourly data for all pollutants during Diwali 2026.
3. What was the official PM2.5 level on Diwali night 2026?
The official average PM2.5 level at 1 AM on Diwali night was 592 µg/m³, about 10 times the 24-hour safe standard.
4. Why do experts think the actual pollution was higher?
Missing readings occurred when pollution neared the instrument limit of 1,000 µg/m³, so discarding them lowered the average. Experts estimate the actual peak was around 800 µg/m³.
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- Original9 November 2026 · Read story
