Patna — Seasonal Pollution Patterns

December is the most polluted month in Patna on average, with a long-run AQI of 304 — firmly in the Very Poor band. This is drawn from 6 CPCB monitoring stations across 9 years of daily readings. Through December, residents should expect elevated PM2.5 and PM10, reduced visibility on cooler mornings, and strong recommendations from doctors to limit outdoor exertion, wear well-fitted N95 masks, and run indoor purifiers through evening and overnight hours when pollutant accumulation typically peaks.

August is the cleanest month of the year in Patna, averaging AQI 76 in the Satisfactory band. The months immediately before and after also tend to sit well below the annual mean of 179, so a visit window centred on August is the safest choice for outdoor sightseeing, marathons, school trips and wedding events. Mornings are usually the crispest time to head out; pollution tends to creep up slightly during the evening commute even in the cleanest months. Always cross-check the day-of live AQI before any high-exertion outdoor plan.

Patna shows a clear monsoon-cleansed signature — rain and deeper atmospheric mixing drop AQI to a seasonal trough, and everything else relative to that trough looks elevated. The specific December spike combines pre-monsoon dust, post-rain rebounds and the arrival of cool-season trapping effects.

Across the CPCB record, the week around Diwali in Patna averages AQI 294 — 1.52× the normal October baseline of AQI 194, a spike of 100 AQI points. Firework particulates combine with a cooler, more stagnant late-October atmosphere to produce some of the worst air-quality days of the entire year. Sensitive groups should treat Diwali eve and the two days after as peak-alert days: stay indoors, close windows by evening, run purifiers on high, and reserve any outdoor celebrations for daytime hours when mixing is strongest.

Yes — meaningfully. Patna's core monsoon window (Jul 15 – Sep 15) averages AQI 100, a 55.6% improvement on the annual mean of 225. Rain removes airborne particulates by wet deposition, and the deeper monsoon boundary layer disperses what remains vertically. Across 980 measured monsoon days we see 48.1% in the Good-or-Satisfactory band.

Between 2016 and 2024, Patna's annual average AQI moved from 212 to 172 — a change of -18.9%. In the most recent year-on-year comparison, the winter season specifically improved by 8.4%. The long-run direction is improving — NCAP policy pressure, cleaner fuels and tighter vehicle standards are showing up.

August is the single best month at AQI 76. Based on the 12-month averages, the three cleanest months in Patna are August (AQI 76), July (AQI 77), September (AQI 79). These are the safest choices for outdoor itineraries, long walks, open-air concerts and day-trips. Sensitive groups can treat these months as near-normal activity windows but should still check live AQI for the specific date. Avoid planning outdoor-heavy trips in December, when the baseline jumps into Very Poor territory.

Patna is classified as monsoon-cleansed. Based on a 12-month cosine-similarity index computed across all monitored Indian cities, the city whose seasonal signature most closely resembles Patna's is Asansol (West Bengal), with its own worst month in December. Cities with similar signatures often respond to similar policy levers — if a neighbouring peer has demonstrated improvements through specific interventions (construction-dust controls, bus electrification, brick-kiln regulation), they are likely candidates for Patna too. The peer-city panel on this page lists the closest four additional matches.