Was October 2026 Delhi's cleanest in years? Yes: the cleanest since at least 2018, with no Very Poor day

Yes. From 1 to 31 October 2026, Delhi's mean 24-hour AQI in CPCB's daily bulletin was 166 (Moderate), the lowest of the nine Octobers in the bulletins since 2018, below 2021 (173) and 26% below 2025 (223). It stays the lowest when Diwali and the three days after it are left out of every year.

The bigger change is at the top end. Delhi had 5 Poor days and no Very Poor day in October 2026, the fewest bad days of any October since 2018. The worst day was 245 on 21 October (CPCB, 21 October), against 373 on 30 October 2025 (CPCB, 30 October 2025).

Key findings

• First of nine, with or without Diwali. Leaving out Diwali and the 3 days after it, 2026 (166) still ranks ahead of 2021 (173) and 2022 (195). Against 2025, the fall is 20%, not 26%. The worst years were 2018 (269) and 2020 (265).
• Early October was not clean. From 1 to 15 October, 2026 averaged 156, worse than 2022 (121), 2025 (144) and 2021 (146). The difference came in the second half.
• Fewest bad days. 5 Poor and none Very Poor, against 18 Poor-or-worse days in 2025 (14 without Diwali) and 8 in 2021.
• Not everywhere. Like for like, 11 of 20 big cities were cleaner than in 2025, led by Chandigarh (down 38%). Ahmedabad, Varanasi, Pune and Bengaluru were worse.

How does October 2026 compare with every October since 2018?

All figures are Delhi's city AQI in CPCB's 4 pm bulletin, the official 24-hour figure, for 1 to 31 October each year. "Like for like" leaves out Diwali day and the 3 days after it. On India's NAQI scale, 101 to 200 is Moderate, 201 to 300 Poor, 301 to 400 Very Poor and above 400 Severe.

Day counts are for all 31 days. The only Severe days were at the very end of the month: 401 on 30 October 2018, and 419 and 410 on 30 and 31 October 2019. Diwali dates are the central government's gazetted holiday (timeanddate.com, India holidays 2018, 2019, 2020, 2021 to 2026).

October 2026 was the steadiest month in the set: Delhi sat in the Moderate band on 23 of 31 days, more than in any other year. It dipped to Satisfactory three times, 83 on 12 October, 90 on 16 October (CPCB, 12 October) and 60 on 30 October, and crossed 200 five times: 245, 223 and 230 from 21 to 23 October, then 229 and 222 on 28 and 29 October (CPCB, 29 October). The middle day of the month, the median, was 174, against 233 in 2025.

The 60 on 30 October is the lowest October reading for Delhi in 2026, and the bulletin named carbon monoxide, not PM2.5, as the main pollutant that day (CPCB, 30 October). IMD had forecast light rain with thunderstorms and gusty winds for 29 and 30 October (our Cyclone Arnab report). The next day, Delhi was back at 117.

2021 got its low mean partly from very clean days after heavy rain. Delhi's AQI was 46 (Good) on 18 October 2021 (CPCB, 18 October 2021), the day 87.9 mm of rain fell at Safdarjung (IMD, below). It also had 8 Poor days, three more than 2026.

Does the headline survive the Diwali test?

Yes. Diwali fireworks push up the next few days' AQI, and Diwali moves by up to three weeks. In 2025 it fell on 20 October, and 20 to 23 October averaged 339. In 2026 it falls on 8 November. So a plain October mean flatters 2026 against 2019, 2022, 2024 and 2025.

We checked two fairer measures:

1. Leaving out Diwali and the 3 days after it. 2026 (166) is still first, ahead of 2021 (173) and 2022 (195). The change from 2025 shrinks from minus 26% to minus 20% (206 to 166).
2. 1 to 15 October only, before Diwali every year and before the usual peak of crop burning. Here 2026 (156) is only fourth.

So "cleanest since 2018" holds for the month, but not for the first half. From 16 to 31 October, with Diwali days left out, Delhi averaged 175 in 2026, against 284 in 2025 and 199 in 2021.

Why was October 2026 cleaner? What we know and what we don't

The bulletins show how much cleaner the air was, not why. Farm fires and rain are the usual suspects.

Farm fires were about the same as 2025. Punjab counted 574 farm fires from 15 September to 24 October 2026, against 561 in 2025 and 1,678 in 2024 (Outlook, 25 October 2026). Yet Delhi's late October was far cleaner this year. Our Punjab stubble burning report has the district figures.

Sources: 2018 to 2023 totals and the 29 October counts, Punjab Remote Sensing Centre and PPCB data via PTI, 29 October 2024; 2024 and 2025 totals, Rozana Spokesman, 16 October 2026; 24 October counts, Outlook, 25 October 2026.

Punjab's fires fell by about nine-tenths from 2018 to 2025, but Delhi's October did not improve in step: 2025, with the fewest fires, was only fourth-cleanest like for like. Most fires come after October.

Rain explains the two clean years before this one. The two wettest Octobers at Safdarjung since 1961 were 2022 (128.6 mm) and 2021 (122.5 mm), according to the India Meteorological Department (IMD). They were also Delhi's two cleanest Octobers in the bulletins before 2026. October 2025 was the third wettest (89.3 mm), but the rain days IMD recorded all fell between 1 and 8 October (IMD monthly weather report for Delhi, October 2025); its first half was clean (144) and its second half was not. Safdarjung had no October rain at all in 2018, 2020 and 2024, the three years with the highest like-for-like means (IMD, Safdarjung October records).

October 2026 had less of that help. IMD's rainfall total for the month is not out yet. A Climate Trends analysis put September-October 2026 rainfall 78.2% below the same period of 2025, with El Niño strengthening (PTI via The Tribune, 28 October 2026). The sharp dips, to 83 on 12 October, 90 on 16 October and 60 on 30 October, each came with rain or a rain forecast (our rain report).

We have not checked wind or Delhi's own emissions, so we can't say what made the difference. See why Delhi's air turns toxic every winter for the usual causes.

Which Indian cities had cleaner air than last October?

The table compares 20 large cities in CPCB's bulletin, 1 to 31 October 2025 and 2026, sorted by the 2026 mean. "Like for like" leaves out Diwali 2025 (20 October) and the 3 days after it from both years.

Changes use unrounded means. Faridabad had no bulletin value on 29 October 2025 or 6 October 2026; every other city has all 31 days in both years.

• Diwali changes the picture. On plain means, 13 of 20 cities were cleaner than in 2025. Like for like, it is 11: Kanpur and Kolkata flip to worse.
• The north improved most. Chandigarh, Noida, Delhi, Jaipur and Ghaziabad all fell by 19% or more like for like.
• Ghaziabad and Noida were still the worst, with 14 and 12 Poor-or-worse days. Noida peaked at 281 on 4 October (CPCB, 4 October).
• The west and south got worse. Pune rose from 87 to 112 and Ahmedabad from 103 to 137. We have not checked the weather there, so we can't say why.

For the full October ranking of every city in the bulletin, see the most polluted cities in India in October 2026.

What others have reported

• Envirocatalysts. The Delhi think tank found every major pollutant lower in October 2026 than in most earlier years. Its PM2.5 average for 1 to 25 October 2026 was 67 µg/m³, the lowest in its table back to 2015, against 75 for the whole of October 2021 and 108 for October 2025 (The Pioneer, 27 October 2026). It compares a part month with full months, so it is not like for like, but it points the same way as the bulletins.
• Climate Trends. Its analysis, reported by PTI on 28 October, found Delhi's mean AQI fell 15.8%, from 169.3 to 142.6, from September-October 2025 to 2026, while the median rose from 135 to 154 (PTI via The Tribune, 28 October 2026). That report includes September, does not give exact dates, and its 2025 window includes Diwali, so it differs from ours.
• CAQM. As of 1 November we found no full-month October figure from CPCB or the Commission for Air Quality Management (CAQM). CAQM put Delhi's September 2026 average at 102, the lowest September in five years (Organiser, 1 October 2026).

What happens next

Diwali is on Sunday 8 November 2026. Last year Delhi was Very Poor on Diwali and each of the 3 days after it, at 305 to 353. Our Diwali 2026 air quality guide covers the firecracker rules and how to protect your home. For today's reading, see the Delhi live page and the Delhi air pollution tracker.

How we measured

• Data. CPCB's 4 pm daily AQI bulletin: each city's AQI over the past 24 hours, averaged across its monitors. We used all 279 bulletins for 1 to 31 October, 2018 to 2026; none was missing. Good Air's own monitor archive starts in September 2026, so it is not used here.
• Checks. A script read every city row and checked the row count against the bulletin's serial numbers and the date against the file. On 2 October 2018 some values were printed without a band after a recalculation; we used the value (Delhi 200) and assigned the band.
• Means and bands. Means of daily bulletin values, on India's National AQI bands: 0 to 50 Good, 51 to 100 Satisfactory, 101 to 200 Moderate, 201 to 300 Poor, 301 to 400 Very Poor, above 400 Severe.
• Diwali. "Like for like" leaves out the gazetted Diwali date and the 3 days after it that fall in October: 4 days in 2019 (27 to 30 October), 4 in 2022, 4 in 2025 and 1 in 2024 (31 October).
• Network changes. The Delhi average used 31 stations on 15 October 2018 and 56 on 15 October 2026, so treat small gaps between years, such as 2026 against 2021, with care.