Delhi's October average AQI falls to 166, but not every pollution measure improves

Clear improvement from a year earlier, but monthly and year-to-date comparisons differ

India's Ministry of Environment, Forest and Climate Change announced through the Press Information Bureau on October 31 that Delhi's average air quality index (AQI) for October 2026 was 166, below 223 in the same month of 2025. It was the lowest October reading among the years 2018–2026 listed in the release. The figure represents the monthly average from October 1 through 31, not air quality on a particular day or at a particular moment.¹

A second set of figures covers a longer period: from January 1 through October 31, Delhi's average AQI was 167, compared with 170 a year earlier. “This October was better than last October” and “the first ten months were slightly better than the equivalent period last year” can therefore both be true, but are not interchangeable. A marked monthly improvement does not mean every month improved by the same amount. Nor can the first ten months' average stand in for the unfinished full year.¹

Archival photograph: sunset on a Delhi street, August 19, 2026. Photograph by Mrstulipsua; Delhi skyline.jpg, used under CC BY 4.0. The photograph does not represent October AQI measurements.

Particulate readings did not all decline

The release reported 220 days with daily average AQI below 200 during January–October, compared with 200 days in the equivalent period a year earlier. This counts days within a specified range; it is not the same statistic as averaging readings over the entire period. The count of 220 days does not establish precise pollution levels on the remaining dates, and an average cannot reconstruct daily fluctuations.¹

Individual pollutants also moved in different directions. Year-to-date average PM2.5 concentration through October 29 was 69 micrograms per cubic meter, compared with 72 a year earlier. PM10 was 171 micrograms per cubic meter, above the previous year's 166. The reporting period for these concentrations ended two days earlier than the AQI comparison. The AQI, particulate concentrations and counts of days within a given range answer different questions; they cannot be combined into a claim that “all pollution indicators declined.”¹

The new official statistics thus support an improvement in the monthly composite indicator while leaving component changes that warrant further analysis. Falling PM2.5 and rising PM10 are not contradictory: they are different statistical measures. This summary release alone cannot establish how much each pollution source contributed to the changes, or whether conditions were consistent across different parts of the city.

A lower average is not a complete explanation of policy effects

A lower monthly average does not by itself prove how much a particular pollution-control measure achieved. Comparisons between years also need to distinguish possible influences such as weather, pollution transport, the timing of festivals, monitoring coverage and local emissions. This release offers no factor-by-factor attribution. Assigning the entire change to one policy would go beyond what the available material supports.

What merits continued attention is daily AQI, concentrations of different particulates and developments during the approaching winter, rather than presenting October's improvement as advance proof that winter pollution has been resolved. Statistical improvement is worth recording, but the distance between that result and sustained, stable improvement across all indicators still needs to be tested against subsequent data.

Source notes

1. 2026-10-31 21:22 (India time) · Delhi Records Lowest Average AQI for October in the Last Eight Years at 166 · Ministry of Environment, Forest and Climate Change / Press Information Bureau, India. Government release material used under the PIB copyright policy; the separate reporting periods for each indicator are retained. ↩ ↩² ↩³ ↩⁴