Report · 18 October 2026

500 AQI at ITO, 24 hours to 4 PM, 18 October 2026, the worst monitor in Delhi today, Severe on CPCB's documented formula, and PM10 set that figure. 9.4 lakh people live within 4 km of it.

193.8

TODAY

Delhi's AQI calculated with CPCB's documented formula, the mean of 58 stations.

1.70 crore

NEAR POOR OR WORSE

Within 4 km of 24 Poor-or-worse monitors: 75.2 per cent of Delhi, every pollutant counted.

6.1x

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, 4.7 MB

Narrated in Hindi. Runs 80 seconds.

The day in brief

Today, 18 October 2026, 24 hours to 4 PM: Delhi's AQI was 193.8, Moderate, calculated with CPCB's documented formula as the mean of 58 stations' AQIs (CPCB's note "How is AQI calculated?" and its AQI Calculator; page 34 sets out the formula). As measured, 45 of the 45 monitors reading PM2.5 were above the WHO 24-hour guideline of 15 µg/m³. Above AQI 200 today: 24 stations, ITO 500, Vivek Vihar 311, Jahangirpuri 308, Rohini 296, and 20 more in the station table. Poor or worse air reached 1.70 crore people within 4 km of their monitor today, 75.2 per cent of Delhi.

The year so far, 1 January to 17 October: 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 90.3 on the same dates of 2025. The middle day reads 151.1 against 137.1 on the same dates last year. On an average day, 26.7 per cent of Delhi's reporting monitors, about 11 of 44, sat above 200 on the particle AQI.

The findings

What the report says

Against yesterday: the one-day move

From 162 to 190. On the 56 stations that reported on both days, the 95 per cent interval runs 16.2 to 39.9 points.

Against last year: the observed reading

Today 194 across 58 stations. The year is judged on the 38 matched stations: 221 today against 279, the mean of the same date ±7 days of 2025 at those stations. The interval runs -82.1 to -35.3 points.

The worst station in the city today

Severe, set by PM10. Its PM10 averaged 533.7 µg/m³ over the 24 hours to 4 PM, 11.8 times the WHO 24-hour guideline of 45 µg/m³. Last year this station read 275 on the mean of the same date ±7 days, so the change is +224.5 points. 9.4 lakh people live within 4 km of this monitor. Within 500 m of the monitor, 60% of the land is built up and 40% is under vegetation, so this reading describes a mixed neighbourhood.

The year, from its best days to its worst

On the same 290 complete dates, 1 January to 17 October, the best tenth of days reads 75.2 against 72.0 and the worst tenth 288.3 against 280.1. The days at or below 200 went from 211 to 212.

How much of the city was above AQI 200

That is 11.2 of 43.6 reporting stations, against 25.8 per cent over the same dates last year, a change of +0.9 points on an interval of -4.3 to +6.0, 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 44 per cent, and within 500 m only 3.5 per cent. The map holds 55 monitors in 53 zones; 58 monitors reported today. 33 of the 53 zones stretch past our chosen 4 km proximity threshold, informed by US EPA neighbourhood-scale guidance.

What each monitor's reading speaks for

That is 75.2 per cent of Delhi, living around the 24 monitors that read Poor or worse. ITO was worst at 500, and 9.4 lakh people live within 4 km of it. This counts people near the monitors, not measured individual exposure.

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