SmogRank / United States / Oregon / Gresham
Gresham, month by month
Gresham has a measured daily mean on 1,200 days since 1 January 2023. Its worst month was August 2026, at 56 US AQI (11.8 µg/m³), 585th of 2,896 cities on that month's world ranking. Its cleanest was July 2025, at 15 US AQI (2.7 µg/m³). 2025 averaged 27 US AQI (4.8 µg/m³), against 26 US AQI (4.7 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
5 months
| Month | Why |
|---|---|
| Feb 2024 | 11 of 29 days measured; a month needs 21. The others: 1 missing from OpenAQ's archive, 17 with under 18 hours of readings or readings that failed our checks. |
| Jan 2024 | No day measured. The others: 31 with under 18 hours of readings or readings that failed our checks. |
| Dec 2023 | 1 of 31 days measured; a month needs 22. The others: 30 with under 18 hours of readings or readings that failed our checks. |
| Mar 2023 | 9 of 31 days measured; a month needs 22. The others: 20 missing from OpenAQ's archive, 2 with under 18 hours of readings or readings that failed our checks. |
| 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.
Gresham's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| August 2026 | 5611.8 µg/m³ | 585thof 2,896 | North-western United States and Canada, 4 to 22 August 2026 |
| August 2023 | 427.6 µg/m³ | 1,122ndof 1,980 | North-western United States and Canada, August 2023 |
| November 2023 | 397.0 µg/m³ | 1,448thof 2,243 | – |
| January 2026 | 366.5 µg/m³ | 1,956thof 2,617 | – |
| September 2025 | 366.4 µg/m³ | 1,933rdof 3,104 | – |
| November 2025 | 366.4 µg/m³ | 2,076thof 2,715 | – |
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.
Gresham's worst days
| Day | US AQI | Episode |
|---|---|---|
| 5 Aug 2026 | 16879.9 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 4 Aug 2026 | 14854.4 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 20 Aug 2023 | 11641.5 µg/m³ | North-western United States and Canada, August 2023 |
| 17 Feb 2024 | 11541.1 µg/m³ | – |
| 6 Aug 2026 | 10637.4 µg/m³ | North-western United States and Canada, 4 to 22 August 2026 |
| 31 Aug 2026 | 9230.9 µg/m³ | – |
| 18 Feb 2024 | 8225.8 µg/m³ | – |
| 9 Nov 2024 | 7823.8 µg/m³ | – |
| 6 Sept 2024 | 7421.4 µg/m³ | – |
| 19 Jul 2023 | 7220.3 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, Gresham, 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/gresham/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.
Gresham 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).