Delhi Records Lowest Average AQI for October in the Last Eight Years at 166

The Air Quality Index, or AQI, is a numerical way to describe overall air pollution and its potential health concern. It combines pollution measurements into one public-facing number. Higher values mean more polluted air. The article groups daily averages below 200 as “Good to Moderate” and values above 200 as “Poor to Severe+.”

Delhi’s monthly average AQI for October 2026 was 166. This is below 200, so it was substantially better than a month dominated by daily readings above that threshold. However, 166 is a monthly average, not a claim that every day had the same air quality or that the air was pollution-free.

The result was notable because October 2026 had Delhi’s lowest October average in the article’s 2018–2026 comparison. The next-lowest was 173 in October 2021. Continued monitoring and pollution-control work remain important, since the January–October period still included 84 days above 200.

The October 2026 average AQI was 166, while October 2025 recorded 223. Subtracting the two gives a 57-point improvement. Because AQI rises as pollution worsens, the lower number represents cleaner average air during October 2026 than during October 2025.

The comparison is unusually strong across the full period. October averages were 234 in 2024, 219 in 2023, 210 in 2022, 173 in 2021, 265 in 2020, 234 in 2019, and 269 in 2018. Even the previous low, 173 in 2021, was seven points higher than 2026’s 166.

These figures show a clear improvement for October, but they do not describe every day individually. The broader January–October average was 167, and the period still had 84 days with daily AQI above 200. Monthly and longer-period averages therefore need to be read alongside daily categories.

The two counts divide January through October 2026 by daily average AQI. A Good-to-Moderate day had an AQI below 200, while a Poor-to-Severe+ day had an AQI above 200. Delhi recorded 220 days in the first group and 84 in the second.

That means cleaner-category days outnumbered more polluted-category days by 136. Together, the counts cover 304 days, matching the length of the January–October period in 2026. The pattern was better than 2025, which had 200 Good-to-Moderate days and 104 Poor-to-Severe+ days.

The improvement also stands out against several earlier years. The 220 cleaner days were higher than every listed year except 2020’s 224, while 84 polluted days were fewer than every listed year except 2020’s 81. Still, 84 days above 200 remain a substantial pollution burden, so CAQM’s continuing control efforts matter.

PM2.5 improved from 72 µg/m³ in 2025 to 69 µg/m³ in 2026, a decrease of 3 µg/m³. PM10 moved in the opposite direction, rising from 166 to 171 µg/m³, an increase of 5 µg/m³. The two measures can change differently because they represent different particle-size ranges and sources.

The article gives no causal explanation for this split. It reports averages for 1 January–29 October and compares them with earlier years. PM2.5 in 2026 was lower than every listed comparison year, while PM10 was higher than 2025 but lower than all listed years from 2024 through 2018.

Therefore, the figures show a mixed particulate-pollution picture, not a uniform improvement. PM2.5 was better than recent comparisons, but PM10 worsened slightly from 2025. More detailed source and weather analysis would be needed to explain why these pollutants diverged.

PM2.5 refers to fine particles with diameters of 2.5 micrometres or less. PM10 includes particles with diameters of 10 micrometres or less, so it includes PM2.5 plus larger particles. Both are measured as concentrations, commonly in micrograms per cubic metre. The article reports both measures for Delhi.

Their sizes help explain different health effects. Fine PM2.5 can travel deeper into the respiratory system and may enter the bloodstream. Larger PM10 particles are more likely to deposit in the nose, throat, and upper airways. Both can irritate the respiratory system and worsen health, although risks depend on concentration, exposure time, and individual vulnerability.

Delhi’s 2026 averages illustrate why both measures matter. PM2.5 was 69 µg/m³ through 29 October, compared with 72 in 2025. PM10 was 171, compared with 166 in 2025. One pollutant improved while the other increased, so air quality cannot be judged from only one particle measure.

The article reports Delhi’s AQI and particulate averages but does not explain the weather or human causes behind them. Based on established air-pollution science, weather strongly affects concentration. Wind can disperse pollutants, while rain can remove particles from the air. Calm conditions can allow pollution to accumulate near the ground.

Seasonal changes also matter. October and winter can bring cooler, more stable air that limits vertical mixing. Delhi may then experience higher concentrations when emissions continue. Human sources can include traffic, industry, construction dust, waste burning, and seasonal agricultural burning, though the article does not attribute 2026’s figures to any of these sources.

The 2026 data show a better October average AQI of 166 and 220 Good-to-Moderate days through October. Yet 84 days were above 200. This contrast suggests that conditions vary over time. CAQM’s planned intensified efforts will be important as Delhi-NCR moves into the coming days.

Repeated days with AQI above 200 mean people are regularly exposed to higher pollution levels. Established health evidence links prolonged particulate exposure with irritation, breathing difficulty, asthma aggravation, and increased cardiovascular and respiratory risks. Pollution can also reduce visibility, stress vegetation, and deposit particles on soil and water. The article itself reports the AQI counts but does not list these consequences.

Delhi recorded 84 Poor-to-Severe+ days from January through October 2026. That is fewer than the 104 such days in both 2025 and 2024, but it still represents many days with daily average AQI above 200. Exposure risk depends on the pollutant, concentration, duration, and a person’s health and activity.

The article says CAQM is working with stakeholders on prevention, control, and abatement of air pollution in Delhi-NCR. Those efforts can include coordinated action, monitoring, and stronger implementation of pollution controls. The agency says these efforts will be intensified to improve air quality in coming days.