Portland, ME Air Quality in October
Across 2019–2025, Portland's October air quality had a median AQI of 32 (Good) over 217 monitored days in the Portland-South Portland, ME area. 0.5% of October days (1 of 217) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 58.5% of days. The cleanest October on record here was 2021 (median AQI 29, 0 days above 100) and the worst was 2023 (median 34, 1 day above 100, peak AQI 120).
- Good: 88.5%
- Moderate: 11.1%
- Unhealthy for Sensitive Groups: 0.5%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Portland
Today's main pollutant in Portland is ground-level ozone (AQI 29). Important: standard HEPA filters do NOT remove ozone — only a purifier with a substantial activated-carbon bed adsorbs it. The biggest wins are cutting indoor sources (gas appliances, certain "ionizer" purifiers) and ventilating when outdoor ozone is low (early morning). A high-carbon unit helps with the gases and VOCs that linger indoors.
Recommended: Levoit Core 300 — True HEPA + activated carbon · CADR ~141 CFM · rooms up to 219 sq ft
As an Amazon Associate, we earn from qualifying purchases.
How is the air in Portland in October?
Good on a typical day: median AQI 32 across 2019–2025, with 0.5% of October days above AQI 100. Ground-level ozone is the main driver.
- ✓88.5% of October days were Good (AQI 0–50), 11.1% Moderate (51–100).
- ✓1 day of 217 reached AQI 101+; the October peak was 120.
- ✓Best October: 2021; worst October: 2023.
Frequently asked questions
What is the air quality like in Portland in October?▾
Across 2019–2025, the median daily AQI in Portland in October was 32 (Good). 88.5% of days were Good, 11.1% Moderate, and 0.5% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is October a good time for outdoor exercise in Portland?▾
A typical October day in Portland sits in the Good range (median AQI 32), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of October days reached AQI 101+ in 2019–2025.
Which pollutant causes Portland's October air quality problems?▾
Ground-level ozone set the daily AQI on 58.5% of October days in Portland. The highest October AQI recorded in 2019–2025 was 120 (Unhealthy for Sensitive Groups), in 2023.
Portland October air quality, year by year
Portland October air quality by year (Portland-South Portland, ME, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 31 | 45 | 0 | 56 | PM2.5 |
| 2020 | 31 | 30 | 0 | 49 | O3 |
| 2021cleanest | 31 | 29 | 0 | 46 | O3 |
| 2022 | 31 | 29 | 0 | 67 | O3 |
| 2023worst | 31 | 34 | 1 | 120 | PM2.5 |
| 2024 | 31 | 31 | 0 | 60 | O3 |
| 2025 | 31 | 29 | 0 | 74 | O3 |
What October air means in Portland
A typical October day in Portland sits in the Good range (median AQI 32), so running, cycling and children's outdoor play are fine for everyone on most days; fewer than 1% of October days reached AQI 101+ in 2019–2025.
October's median AQI of 32 is below Portland's whole-year median of 40, making it one of the area's cleaner periods. Nationally, the median October AQI across every EPA metro area (102,872 metro-days, 2019–2025) is 38, so Portland runs below the national October norm; 0.5% of its October days topped AQI 100 versus 1.3% nationally (about the same).
October is part of Portland's fall season (September, October, November); the fall page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Portland
The latest EPA AirNow observation puts Portland's AQI at 29 (O3). The figures above are multi-year month statistics, not today's reading.
View current Portland air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Portland-South Portland, ME), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.