SmogRank / United States / Maine / Portland
Portland, month by month
Portland, Maine has a measured daily mean on 1,354 days since 1 January 2023. Its worst month was July 2023, at 57 US AQI (12.1 µg/m³), 391st of 1,432 cities on that month's world ranking. Its cleanest was March 2023, at 19 US AQI (3.5 µg/m³). 2025 averaged 37 US AQI (6.7 µg/m³), against 32 US AQI (5.8 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
Portland's worst months
| Month | US AQI | World rank | Episode |
|---|---|---|---|
| July 2023 | 5712.1 µg/m³ | 391stof 1,432 | United States and Canada, July 2023 Eastern United States and Canada, June and July 2023 |
| July 2026 | 5511.5 µg/m³ | 996thof 2,784 | Northern United States and Canada, July 2026 |
| September 2023 | 5410.7 µg/m³ | 472ndof 2,176 | North-eastern United States and Canada, September and October 2023 Eastern Canada and United States, September 2023 |
| February 2026 | 5410.6 µg/m³ | 1,274thof 2,866 | – |
| January 2026 | 5410.5 µg/m³ | 1,035thof 2,617 | – |
| July 2025 | 529.9 µg/m³ | 1,283rdof 2,889 | North-eastern United States and Canada, 29 July to 9 August 2025 North-eastern United States and Canada, 24 to 28 July 2025 |
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.
Portland's worst days
| Day | US AQI | Episode |
|---|---|---|
| 26 Jul 2025 | 11039.1 µg/m³ | North-eastern United States and Canada, 24 to 28 July 2025 |
| 1 Oct 2023 | 10236.1 µg/m³ | North-eastern United States and Canada, September and October 2023 |
| 6 Sept 2023 | 9532.6 µg/m³ | Eastern Canada and United States, September 2023 |
| 18 Jul 2026 | 9532.6 µg/m³ | Northern United States and Canada, July 2026 |
| 4 Aug 2025 | 9331.5 µg/m³ | North-eastern United States and Canada, 29 July to 9 August 2025 |
| 7 Sept 2023 | 9230.9 µg/m³ | – |
| 8 Jun 2025 | 9029.8 µg/m³ | Northern United States and Canada, May and June 2025 |
| 18 Jul 2023 | 8828.7 µg/m³ | United States and Canada, July 2023 |
| 9 Jun 2025 | 8326.5 µg/m³ | Northern United States and Canada, May and June 2025 |
| 9 Sept 2023 | 8326.3 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, Portland, Maine, 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/portland-maine/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.
Portland now: the last 24 hours, its ranks today and the last 12 months day by day.
Updated 2026-10-12 19:07 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).