Boise Air Quality in January
Across 2019–2025, Boise's January air quality had a median AQI of 58 (Moderate) over 217 monitored days in the Boise City, ID area. 1.8% of January days (4 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 100.0% of days. The cleanest January on record here was 2025 (median AQI 54, 0 days above 100) and the worst was 2024 (median 56, 4 days above 100, peak AQI 157).
- Good: 11.1%
- Moderate: 87.1%
- Unhealthy for Sensitive Groups: 0.9%
- Unhealthy or worse: 0.9%
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.
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How is the air in Boise in January?
Moderate on a typical day: median AQI 58 across 2019–2025, with 1.8% of January days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓11.1% of January days were Good (AQI 0–50), 87.1% Moderate (51–100).
- ✓4 days of 217 reached AQI 101+; the January peak was 157.
- ✓Best January: 2025; worst January: 2024.
Frequently asked questions
What is the air quality like in Boise in January?▾
Across 2019–2025, the median daily AQI in Boise in January was 58 (Moderate). 11.1% of days were Good, 87.1% Moderate, and 1.8% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is January a good time for outdoor exercise in Boise?▾
A typical January day in Boise is Moderate (median AQI 58): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 56 of January days (1.8%) 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 January air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 100.0% of January days in Boise. The highest January AQI recorded in 2019–2025 was 157 (Unhealthy), in 2024.
Boise January air quality, year by year
Boise January air quality by year (Boise City, ID, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 31 | 63 | 0 | 88 | PM2.5 |
| 2020 | 31 | 56 | 0 | 79 | PM2.5 |
| 2021 | 31 | 60 | 0 | 80 | PM2.5 |
| 2022 | 31 | 59 | 0 | 76 | PM2.5 |
| 2023 | 31 | 56 | 0 | 70 | PM2.5 |
| 2024worst | 31 | 56 | 4 | 157 | PM2.5 |
| 2025cleanest | 31 | 54 | 0 | 82 | PM2.5 |
What January air means in Boise
A typical January day in Boise is Moderate (median AQI 58): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 56 of January days (1.8%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
January's median AQI of 58 is above Boise's whole-year median of 54, making it one of the area's dirtier periods. Nationally, the median January AQI across every EPA metro area (95,602 metro-days, 2019–2025) is 39, so Boise runs above the national January norm; 1.8% of its January days topped AQI 100 versus 0.7% nationally (above average).
January is part of Boise's winter season (December, January, February); the winter page pools all three months.
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 month 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.