SmogRank / United States / Colorado / Littleton
Littleton, month by month
Littleton has a measured daily mean on 751 days since 17 April 2024. Its worst month was October 2024, at 52 US AQI (9.5 µg/m³), 572nd of 2,020 cities on that month's world ranking. Its cleanest was September 2026, at 16 US AQI (2.9 µg/m³).
Every month since 2024
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
6 months
| Month | Why |
|---|---|
| Jul 2026 | 8 of 31 days measured; a month needs 22. The others: 23 with under 18 hours of readings or readings that failed our checks. |
| Jun 2026 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| May 2026 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Apr 2026 | No day measured. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Mar 2026 | 10 of 31 days measured; a month needs 22. The others: 21 with under 18 hours of readings or readings that failed our checks. |
| Apr 2024 | 14 of 30 days measured; a month needs 21. |
A day counts once 18 hours of it are measured; a month needs 70% of its days.
Littleton's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| October 2024 | 529.5 µg/m³ | 572ndof 2,020 | – |
| August 2026 | 498.9 µg/m³ | 1,219thof 2,896 | North-western United States and Canada, July and August 2026 |
| July 2024 | 458.1 µg/m³ | 1,307thof 2,566 | – |
| February 2025 | 448.0 µg/m³ | 1,586thof 2,633 | – |
| September 2025 | 325.8 µg/m³ | 2,193rdof 3,104 | – |
| January 2025 | 325.7 µg/m³ | 2,066thof 2,474 | – |
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.
Littleton's worst days
| Day | US AQI | Episode |
|---|---|---|
| 4 Aug 2026 | 8829.1 µg/m³ | North-western United States and Canada, July and August 2026 |
| 5 Aug 2026 | 7823.6 µg/m³ | – |
| 5 Sept 2025 | 7723.3 µg/m³ | – |
| 23 Jul 2024 | 7723.2 µg/m³ | – |
| 7 Aug 2026 | 7722.8 µg/m³ | – |
| 24 Jul 2024 | 7521.9 µg/m³ | – |
| 1 Oct 2024 | 7521.9 µg/m³ | – |
| 6 Aug 2026 | 7019.3 µg/m³ | – |
| 20 Feb 2025 | 7019.1 µg/m³ | – |
| 3 Aug 2026 | 7019.1 µg/m³ | North-western United States and Canada, July and August 2026 |
Daily means, the highest since 17 Apr 2024; 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, Littleton, United States, 17 Apr 2024 – 11 Oct 2026. Monitor data from AirNow, via OpenAQ and from the publisher directly; sources listed at smogrank.com/sources. smogrank.com/us/littleton/history (accessed 13 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.
Littleton now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-13 00:07 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).