SmogRank / United States / Washington / Chehalis
Chehalis, month by month
Chehalis has a measured daily mean on 1,256 days since 1 January 2023. Its worst month was November 2023, at 52 US AQI (9.7 µg/m³), 696th of 2,243 cities on that month's world ranking. Its cleanest was May 2025, at 15 US AQI (2.7 µg/m³). 2025 averaged 26 US AQI (4.6 µg/m³), against 26 US AQI (4.6 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
4 months
| Month | Why |
|---|---|
| Nov 2025 | 18 of 30 days measured; a month needs 21. The others: 12 with under 18 hours of readings or readings that failed our checks. |
| Aug 2025 | 3 of 31 days measured; a month needs 22. The others: 28 with under 18 hours of readings or readings that failed our checks. |
| Mar 2023 | 11 of 31 days measured; a month needs 22. The others: 20 missing from OpenAQ's archive. |
| Feb 2023 | 1 of 28 days measured; a month needs 20. The others: 25 missing from OpenAQ's archive, 2 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.
Chehalis's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| November 2023 | 529.7 µg/m³ | 696thof 2,243 | – |
| January 2025 | 529.6 µg/m³ | 1,064thof 2,474 | – |
| January 2026 | 519.2 µg/m³ | 1,203rdof 2,617 | Washington and Oregon, United States, January 2026 |
| October 2023 | 448.0 µg/m³ | 764thof 2,012 | – |
| August 2026 | 447.9 µg/m³ | 1,670thof 2,896 | North-western United States and Canada, 4 to 22 August 2026 |
| August 2023 | 437.7 µg/m³ | 1,101stof 1,980 | North-western United States and Canada, August 2023 |
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.
Chehalis's worst days
| Day | US AQI | Episode |
|---|---|---|
| 5 Aug 2026 | 12043.2 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 20 Aug 2023 | 10436.7 µg/m³ | North-western United States and Canada, August 2023 |
| 4 Aug 2026 | 9432.3 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 5 Jul 2023 | 9130.7 µg/m³ | Washington, United States, July 2023 |
| 25 Jan 2026 | 8326.4 µg/m³ | Washington and Oregon, United States, January 2026 |
| 29 Nov 2023 | 7723.2 µg/m³ | – |
| 9 Nov 2024 | 7622.3 µg/m³ | – |
| 31 Oct 2023 | 7421.7 µg/m³ | – |
| 28 Jan 2025 | 7421.4 µg/m³ | – |
| 6 Aug 2026 | 7320.9 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
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, Chehalis, 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/chehalis/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.
Chehalis now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 17:07 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).