Boise Air Quality in Fall
Across 2019–2025, Boise's fall (September–November) air quality had a median AQI of 56 (Moderate) over 637 monitored days in the Boise City, ID area. 8.5% of fall days (54 of 637) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 83.0% of days. The cleanest fall on record here was 2025 (median AQI 50, 0 days above 100) and the worst was 2024 (median 63, 23 days above 100, peak AQI 265).
- Good: 35.2%
- Moderate: 56.4%
- Unhealthy for Sensitive Groups: 4.9%
- Unhealthy or worse: 3.6%
Reduce Indoor Ozone in Boise
Today's main pollutant in Boise is ground-level ozone (AQI 38). 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 Boise in fall?
Moderate on a typical day: median AQI 56 across 2019–2025, with 8.5% of fall days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓35.2% of fall days were Good (AQI 0–50), 56.4% Moderate (51–100).
- ✓54 days of 637 reached AQI 101+; the fall peak was 265.
- ✓Cleanest month: November; worst month: September.
Frequently asked questions
What is the air quality like in Boise in fall?▾
Across 2019–2025, the median daily AQI in Boise in fall was 56 (Moderate). 35.2% of days were Good, 56.4% Moderate, and 8.5% reached Unhealthy for Sensitive Groups or worse, based on 637 monitored days in EPA's Air Quality System.
Is fall a good time for outdoor exercise in Boise?▾
A typical fall day in Boise is Moderate (median AQI 56): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 12 of fall days (8.5%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Boise's fall air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 83.0% of fall days in Boise. The highest fall AQI recorded in 2019–2025 was 265 (Very Unhealthy), in 2024.
Boise fall air quality, year by year
Boise fall air quality by year (Boise City, ID, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 91 | 54 | 1 | 104 | PM2.5 |
| 2020 | 91 | 62 | 14 | 223 | PM2.5 |
| 2021 | 91 | 55 | 6 | 153 | PM2.5 |
| 2022 | 91 | 64 | 9 | 188 | PM2.5 |
| 2023 | 91 | 48 | 1 | 120 | PM2.5 |
| 2024worst | 91 | 63 | 23 | 265 | PM2.5 |
| 2025cleanest | 91 | 50 | 0 | 97 | PM2.5 |
What fall air means in Boise
A typical fall day in Boise is Moderate (median AQI 56): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 12 of fall days (8.5%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Fall's median AQI of 56 is in line with Boise's whole-year median of 54, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median Fall AQI across every EPA metro area (296,275 metro-days, 2019–2025) is 40, so Boise runs above the national Fall norm; 8.5% of its Fall days topped AQI 100 versus 1.5% nationally (above average).
Within the season, November is the cleanest month (median AQI 61, 1.0% of days above 100) and September the worst (median 55, 17.6% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Boise
The latest EPA AirNow observation puts Boise's AQI at 38 (O3). The figures above are multi-year season statistics, not today's reading.
View current Boise air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Boise City, ID), 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.