Portland, ME Air Quality in Summer
Across 2019–2025, Portland's summer (June–August) air quality had a median AQI of 47 (Good) over 644 monitored days in the Portland-South Portland, ME area. 2.1% of summer days (13 of 644) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 54.0% of days. The cleanest summer on record here was 2020 (median AQI 47, 0 days above 100) and the worst was 2025 (median 45, 6 days above 100, peak AQI 169).
- Good: 57.1%
- Moderate: 40.8%
- Unhealthy for Sensitive Groups: 1.9%
- Unhealthy or worse: 0.2%
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 is the air in Portland in summer?
Good on a typical day: median AQI 47 across 2019–2025, with 2.1% of summer days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓57.1% of summer days were Good (AQI 0–50), 40.8% Moderate (51–100).
- ✓13 days of 644 reached AQI 101+; the summer peak was 169.
- ✓Cleanest month: July; worst month: June.
Frequently asked questions
What is the air quality like in Portland in summer?▾
Across 2019–2025, the median daily AQI in Portland in summer was 47 (Good). 57.1% of days were Good, 40.8% Moderate, and 2.1% reached Unhealthy for Sensitive Groups or worse, based on 644 monitored days in EPA's Air Quality System.
Is summer a good time for outdoor exercise in Portland?▾
A typical summer day in Portland sits in the Good range (median AQI 47), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 48 of summer days (2.1%) reached AQI 101+ in 2019–2025.
Which pollutant causes Portland's summer air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 54.0% of summer days in Portland. The highest summer AQI recorded in 2019–2025 was 169 (Unhealthy), in 2025.
Portland summer air quality, year by year
Portland summer 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 | 92 | 52 | 1 | 115 | PM2.5 |
| 2020cleanest | 92 | 47 | 0 | 87 | PM2.5 |
| 2021 | 92 | 39 | 3 | 129 | O3 |
| 2022 | 92 | 38 | 2 | 126 | O3 |
| 2023 | 92 | 51 | 0 | 100 | PM2.5 |
| 2024 | 92 | 51 | 1 | 129 | PM2.5 |
| 2025worst | 92 | 45 | 6 | 169 | PM2.5 |
What summer air means in Portland
A typical summer day in Portland sits in the Good range (median AQI 47), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 48 of summer days (2.1%) reached AQI 101+ in 2019–2025.
Summer's median AQI of 47 is above Portland's whole-year median of 40, making it one of the area's dirtier periods. Nationally, the median Summer AQI across every EPA metro area (308,645 metro-days, 2019–2025) is 46, so Portland runs in line with the national Summer norm; 2.1% of its Summer days topped AQI 100 versus 3.6% nationally (below average).
Within the season, July is the cleanest month (median AQI 52, 1.8% of days above 100) and June the worst (median 44, 2.4% above 100).
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 season 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.