Report · 21 September 2026

235 AQI at Sirifort, 24 hours to 4 PM, 21 September 2026, Poor on CPCB's documented formula, and PM2.5 set that figure. 8.9 lakh people live within 4 km of it.

167.3

TODAY

Delhi's AQI calculated with CPCB's documented formula, the mean of 44 stations.

1.79 crore

NEAR MODERATE OR WORSE

Within 4 km of 43 Moderate-or-worse monitors: 85.7 per cent of Delhi, every pollutant counted.

4.7x

THE WHO 24-HOUR LINE

Delhi's PM2.5 today, as measured, against the WHO 24-hour guideline.

The AQI figures here are calculated with the formula that the Central Pollution Control Board (CPCB) publishes for its air quality index. CPCB's own documents set out that formula: CPCB's note on how the AQI is calculated; CPCB's AQI calculator.

The full report

The complete written report for this day, with every figure and the source it comes from.

Download the daily reportPDF, 2.8 MB

The day in brief

Today, 21 September 2026, 24 hours to 4 PM: Delhi's air today is 48.2 points worse than on this date last year, which is 39.6 per cent higher, on the Central Pollution Control Board's own readings. Delhi's AQI was 167.3, Moderate, calculated with CPCB's documented formula as the mean of 44 stations' AQIs (CPCB's note "How is AQI calculated?" and its AQI Calculator; page 24 sets out the formula). Above AQI 200 today: 4 stations, Sirifort 235, Nehru Nagar 216, Chandni Chowk 214, Patparganj 208. The highest reading anywhere in Delhi today was 260 at IGI Airport (T3), and ozone set that figure. The figure at the head of this page is lower, because this record does not anchor its headline on IGI Airport (T3), whose nitrogen oxide readings fail this record's consistency check; the count below includes every pollutant. Poor or worse air reached 41.7 lakh people within 4 km of their monitor today, 19.9 per cent of Delhi.

The year so far, 1 January to 21 September: the cleaner days of 2026 have been the dirtiest for these dates since 2019, because three days in four read above 106.7 on the particle AQI, against 88.5 on the same dates of 2025. On an average day, 28.3 per cent of Delhi's reporting monitors, about 12 of 43, sat above 200 on the particle AQI.

The findings

What the report says

Against yesterday: the one-day move

From 163 to 167. On the 44 stations that reported on both days, the 95 per cent interval runs -2.8 to 11.2 points, so the honest reading is level, not worse.

Against last year: the observed reading

Today 167 across 44 stations. The year is judged on the 37 matched stations: 170 today against 122, the mean of the same date ±7 days of 2025 at those stations. The interval runs 36.3 to 60.1 points.

The highest particle reading in the city today

Poor, set by PM2.5. Its PM2.5 averaged 100.3 µg/m³ over the 24 hours to 4 PM, 6.6 times the WHO 24-hour guideline of 15 µg/m³. Last year this station read 123 on the mean of the same date ±7 days, so the change is +112.4 points. 8.9 lakh people live within 4 km of this monitor. The highest reading of the day was 260 at IGI Airport (T3), set by ozone. Within 500 m of the monitor, 39% of the land is built up and 61% is under vegetation, so this reading describes a mixed neighbourhood.

The year, from its best days to its worst

On the same 264 complete dates, 1 January to 21 September, the best tenth of days reads 78.1 against 71.9 and the worst tenth 293.0 against 297.2. The days at or below 200 went from 188 to 186.

How much of the city was above AQI 200

That is 11.8 of 43.2 reporting stations, against 26.8 per cent over the same dates last year, a change of +1.4 points on an interval of -3.9 to +7.0, so it is unchanged inside its margin.

Who the monitoring network reaches

Within 4 km live 92 per cent of Delhi's people, within 2 km 45 per cent, and within 500 m only 3.6 per cent. Delhi has 55 monitors in 53 zones, of which 44 reported today, and 30 of the 53 zones stretch past 4 km, the distance that the US EPA's neighbourhood scale treats as the furthest a monitor speaks for.

What each monitor's reading speaks for

That is 19.9 per cent of Delhi, living around the 4 monitors that read Poor or worse. The highest reading this record leads on is Sirifort at 235, and 8.9 lakh people live within 4 km of it; the higher readings it sets aside are named below. On the wider count, 1.79 crore people, 85.7 per cent of Delhi, live within 4 km of a monitor at Moderate or worse.

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