Billings Air Quality in Fall
Across 2019–2025, Billings's fall (September–November) air quality had a median AQI of 36 (Good) over 630 monitored days in the Billings, MT area. 1.0% of fall days (6 of 630) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 86.0% of days. The cleanest fall on record here was 2019 (median AQI 30, 0 days above 100) and the worst was 2020 (median 41, 2 days above 100, peak AQI 126).
- Good: 79.2%
- Moderate: 19.8%
- Unhealthy for Sensitive Groups: 0.8%
- Unhealthy or worse: 0.2%
Reduce Indoor Ozone in Billings
Today's main pollutant in Billings is ground-level ozone (AQI 21). 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 Billings in fall?
Good on a typical day: median AQI 36 across 2019–2025, with 1.0% of fall days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓79.2% of fall days were Good (AQI 0–50), 19.8% Moderate (51–100).
- ✓6 days of 630 reached AQI 101+; the fall peak was 191.
- ✓Cleanest month: November; worst month: September.
Frequently asked questions
What is the air quality like in Billings in fall?▾
Across 2019–2025, the median daily AQI in Billings in fall was 36 (Good). 79.2% of days were Good, 19.8% Moderate, and 1.0% reached Unhealthy for Sensitive Groups or worse, based on 630 monitored days in EPA's Air Quality System.
Is fall a good time for outdoor exercise in Billings?▾
A typical fall day in Billings sits in the Good range (median AQI 36), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 100 of fall days (1.0%) reached AQI 101+ in 2019–2025.
Which pollutant causes Billings's fall air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 86.0% of fall days in Billings. The highest fall AQI recorded in 2019–2025 was 191 (Unhealthy), in 2020.
Billings fall air quality, year by year
Billings fall air quality by year (Billings, MT, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019cleanest | 91 | 30 | 0 | 59 | PM2.5 |
| 2020worst | 91 | 41 | 2 | 126 | PM2.5 |
| 2021 | 89 | 40 | 1 | 126 | PM2.5 |
| 2022 | 91 | 42 | 1 | 107 | PM2.5 |
| 2023 | 87 | 35 | 2 | 191 | PM2.5 |
| 2024 | 90 | 36 | 0 | 100 | PM2.5 |
| 2025 | 91 | 34 | 0 | 91 | O3 |
What fall air means in Billings
A typical fall day in Billings sits in the Good range (median AQI 36), so running, cycling and children's outdoor play are fine for everyone on most days; about 1 day in 100 of fall days (1.0%) reached AQI 101+ in 2019–2025.
Fall's median AQI of 36 is in line with Billings's whole-year median of 38, 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 Billings runs below the national Fall norm; 1.0% of its Fall days topped AQI 100 versus 1.5% nationally (about the same).
Within the season, November is the cleanest month (median AQI 33, 0.0% of days above 100) and September the worst (median 42, 2.9% above 100).
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Billings
The latest EPA AirNow observation puts Billings's AQI at 21 (O3). The figures above are multi-year season statistics, not today's reading.
View current Billings air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Billings, MT), 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.