SmogRank / United States / Idaho / Lewiston
Lewiston, month by month
Lewiston has a measured daily mean on 1,312 days since 1 January 2023. Its worst month was August 2026, at 75 US AQI (21.8 µg/m³), 211th of 2,896 cities on that month's world ranking. Its cleanest was June 2026, at 26 US AQI (4.7 µg/m³). 2025 averaged 49 US AQI (8.9 µg/m³), against 51 US AQI (9.2 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
2 months
| Month | Why |
|---|---|
| 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.
Lewiston's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| August 2026 | 7521.8 µg/m³ | 211thof 2,896 | North-western United States and Canada, 25 to 26 August 2026 North-western United States and Canada, 4 to 22 August 2026and 1 more |
| July 2024 | 7220.4 µg/m³ | 99thof 2,566 | North-western United States and Canada, July 2024 |
| August 2023 | 6818.0 µg/m³ | 154thof 1,980 | North-western United States and Canada, August 2023 |
| July 2026 | 6516.6 µg/m³ | 440thof 2,784 | North-western United States and Canada, July and August 2026 |
| September 2025 | 6114.6 µg/m³ | 352ndof 3,104 | North-western United States and Canada, September 2025 North-western Canada and United States, September 2025and 1 more |
| November 2023 | 5913.2 µg/m³ | 215thof 2,243 | North-western United States and Canada, October and November 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.
Lewiston's worst days
| Day | US AQI | Episode |
|---|---|---|
| 20 Aug 2023 | 198123.0 µg/m³ | North-western United States and Canada, August 2023 |
| 26 Jul 2024 | 189109.9 µg/m³ | North-western United States and Canada, July 2024 |
| 27 Jul 2024 | 15358.0 µg/m³ | North-western United States and Canada, July 2024 |
| 16 Jul 2024 | 15156.2 µg/m³ | – |
| 21 Aug 2023 | 14955.0 µg/m³ | North-western United States and Canada, August 2023 |
| 7 Aug 2026 | 14151.9 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 23 Aug 2025 | 14151.6 µg/m³ | – |
| 28 Jul 2024 | 13750.3 µg/m³ | North-western United States and Canada, July 2024 |
| 24 Aug 2025 | 13549.5 µg/m³ | – |
| 6 Aug 2026 | 12846.6 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, Lewiston, 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/lewiston-idaho/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.
Lewiston now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 22:07 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).