Portland, ME Air Quality in 2025
In 2025, Portland's air quality (Portland-South Portland, ME area) had a median daily AQI of 40 (Good) across 365 monitored days. 6 days (1.6%) reached Unhealthy for Sensitive Groups or worse, 270 were Good, and the year's peak AQI was 169 (Unhealthy). Ground-level ozone set the daily AQI on 229 of those days. The cleanest month of 2025 was October (median AQI 29, 0 days above 100) and the worst was August (median 42, 3 days above 100, peak 169).
- Good: 74.0%
- Moderate: 24.4%
- Unhealthy for Sensitive Groups: 1.4%
- Unhealthy or worse: 0.3%
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
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How was Portland's air quality in 2025?
Good on a typical day: median AQI 40, with 6 days above AQI 100 out of 365 monitored — the 7th cleanest of 7 years on record for the area.
- ✓Peak AQI in 2025: 169 (Unhealthy).
- ✓Ground-level ozone was the main pollutant on 229 days.
- ✓Cleanest month: October; worst: August.
Frequently asked questions
What was the average AQI in Portland in 2025?▾
EPA's Air Quality System puts Portland's (Portland-South Portland, ME) median daily AQI for 2025 at 40, which is Good. 6 days were Unhealthy for Sensitive Groups or worse and the year's highest AQI was 169.
Which month had the worst air quality in Portland in 2025?▾
The cleanest month of 2025 was October (median AQI 29, 0 days above 100) and the worst was August (median 42, 3 days above 100, peak 169).
Was 2025 a good or bad year for Portland's air?▾
Among the 7 years EPA has published for the area (2019–2025), 2025 ranks 7th cleanest by days above AQI 100 — the worst year on record here. 2025's median of 40 is in line with the area's typical annual median of 40.
Portland month by month in 2025
Portland air quality month by month, 2025 (Portland-South Portland, ME, EPA AQS daily AQI)
| Month | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| January | 31 | 41 | 0 | 78 | O3 |
| February | 28 | 43 | 0 | 79 | O3 |
| March | 31 | 44 | 0 | 60 | O3 |
| April | 30 | 46 | 0 | 84 | O3 |
| May | 31 | 39 | 0 | 69 | O3 |
| June | 30 | 42 | 2 | 147 | PM2.5 |
| July | 31 | 51 | 1 | 114 | PM2.5 |
| Augustworst | 31 | 42 | 3 | 169 | O3 |
| September | 30 | 32 | 0 | 56 | O3 |
| Octobercleanest | 31 | 29 | 0 | 74 | O3 |
| November | 30 | 31 | 0 | 57 | O3 |
| December | 31 | 42 | 0 | 63 | PM2.5 |
How 2025 compares
Among the 7 years EPA has published for the area (2019–2025), 2025 ranks 7th cleanest by days above AQI 100 — the worst year on record here.
2025's median of 40 is in line with the area's typical annual median of 40.
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 annual 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.