SmogRank / United States / Colorado / Fort Collins
Fort Collins, month by month
Fort Collins has a measured daily mean on 1,320 days since 1 January 2023. Its worst month was October 2024, at 55 US AQI (11.5 µg/m³), 417th of 2,020 cities on that month's world ranking. Its cleanest was May 2024, at 19 US AQI (3.4 µg/m³). 2025 averaged 36 US AQI (6.5 µg/m³), against 36 US AQI (6.5 µg/m³) in 2024.
Every month since 2023
The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales
Months without a mean, and why
1 month
| Month | Why |
|---|---|
| Dec 2023 | 20 of 31 days measured; a month needs 22. The others: 11 with under 18 hours of readings or readings that failed our checks. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Fort Collins's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| October 2024 | 5511.5 µg/m³ | 417thof 2,020 | – |
| August 2026 | 5410.9 µg/m³ | 718thof 2,896 | North-western United States and Canada, July and August 2026 |
| January 2023 | 5310.3 µg/m³ | 447thof 1,261 | – |
| July 2024 | 519.2 µg/m³ | 951stof 2,566 | North-western United States and Canada, July 2024 |
| August 2025 | 488.7 µg/m³ | 1,578thof 2,901 | – |
| July 2026 | 468.2 µg/m³ | 1,821stof 2,784 | North-western United States and Canada, July and August 2026 |
Monthly means over the days measured; finished months only. World rank: its place on that month's world ranking of every city with enough days. Each month opens that ranking.
Fort Collins's worst days
| Day | US AQI | Episode |
|---|---|---|
| 19 May 2023 | 14653.9 µg/m³ | North-western United States and Canada, May 2023 |
| 3 Aug 2026 | 10035.3 µg/m³ | North-western United States and Canada, July and August 2026 |
| 20 May 2023 | 9633.4 µg/m³ | North-western United States and Canada, May 2023 |
| 4 Aug 2026 | 9230.9 µg/m³ | North-western United States and Canada, July and August 2026 |
| 23 Jul 2024 | 8527.5 µg/m³ | North-western United States and Canada, July 2024 |
| 6 Aug 2025 | 8427.0 µg/m³ | – |
| 7 Aug 2026 | 8326.4 µg/m³ | – |
| 5 Aug 2026 | 8024.5 µg/m³ | – |
| 24 Jul 2024 | 8024.4 µg/m³ | North-western United States and Canada, July 2024 |
| 1 Oct 2024 | 7923.9 µg/m³ | – |
Daily means, the highest since 1 Jan 2023; the WHO's daily guideline is 15 µg/m³. Each date opens that day's world ranking, and each episode the bad-air spell it was part of.
Use this history
SmogRank, PM2.5 monthly and daily means, Fort Collins, United States, 1 Jan 2023 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/fort-collins/history (accessed 12 Oct 2026).
You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.
Fort Collins now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 20:07 UTC. Values are PM2.5 (fine particles), the median of each city's monitors, as the US AQI PM2.5 sub-index. Some low-cost readings: Sensor.Community, ODbL (data and licence). Some readings: Uzhydromet (Uzbekistan's Hydrometeorological Service); Department of Environment, Nepal; Vietnam's government monitors; Aurassure; Umhverfisstofnun (Environment Agency of Iceland); RMCAB (Secretaría Distrital de Ambiente, Bogotá); Love My Air (City and County of Denver), no reuse terms published (why we use them).