Billings Best & Worst AQI Days: Air Quality Guide
The worst air quality day on record for Billings (Billings, MT area) was September 5, 2023, when the daily AQI reached 191 (Unhealthy), set by fine particulate matter (PM2.5), in wildfire smoke season. Across 2,440 monitored days in 2019–2025, 5 of the 10 worst days were Unhealthy (AQI 151+) or worse; 10 of the 10 were driven by fine particulate matter (PM2.5), and 5 of them fell in 2021. The cleanest day was September 18, 2024 at AQI 0 (Good); the 10 best days span 4 different years.
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.
Recommended: Levoit Core 300 — True HEPA + activated carbon · CADR ~141 CFM · rooms up to 219 sq ft
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When were Billings's worst and best air quality days?
Worst: September 5, 2023, AQI 191 (Unhealthy, PM2.5). Best: September 18, 2024, AQI 0 (Good). Based on 2,440 EPA-monitored days in the Billings, MT area, 2019–2025.
- ✓5 of the 10 worst days were Unhealthy (AQI 151+) or worse; the 10th-worst was AQI 126 (Unhealthy for Sensitive Groups).
- ✓Fine particulate matter (PM2.5) drove 10 of the 10 worst days.
- ✓2021 accounts for 5 of the 10 worst days.
Frequently asked questions
What was the worst air quality day in Billings?▾
September 5, 2023: the Billings, MT area's daily AQI hit 191 (Unhealthy), driven by fine particulate matter (PM2.5), in wildfire smoke season. That is the highest of 2,440 monitored days in 2019–2025.
What was the best air quality day in Billings?▾
September 18, 2024, with a daily AQI of 0 (Good). The daily AQI is the highest reading from any monitor in the area, so even the cleanest day reflects the area's worst monitor.
What was Billings's worst air quality day in 2025?▾
September 3, 2025, AQI 91 (Moderate), set by fine particulate matter (PM2.5).
Which pollutant causes Billings's worst air days?▾
Fine particulate matter (PM2.5) set the AQI on 10 of the 10 worst days. The tables above list the defining pollutant for every day.
Billings's 10 worst air quality days, 2019–2025
Highest daily AQI recorded for the Billings, MT area (EPA AQS). The daily AQI is the highest reading from any monitor in the area that day.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2023 page) | 191 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 2 | (2021 page) | 167 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 3 | (2020 page) | 163 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 4 | (2019 page) | 159 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 5 | (2022 page) | 155 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 6 | (2021 page) | 136 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 7 | (2021 page) | 128 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 8 | (2023 page) | 126 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 9 | (2021 page) | 126 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 10 | (2021 page) | 126 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
Worst day of each year in Billings
The single highest-AQI day in each year on record. Click a year for its full month-by-month statistics.
| Year | Worst day | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 2019 | 159 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2020 | 163 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2021 | 167 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2022 | 155 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2023 | 191 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2024 | 105 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season | |
| 2025 | 91 | Moderate | PM2.5 — fine particulate matter (PM2.5) |
Billings's 10 best air quality days, 2019–2025
Lowest daily AQI recorded for the Billings, MT area. Ties are listed most recent first.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2024 page) | 0 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 2 | (2023 page) | 2 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 3 | (2023 page) | 3 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 4 | (2023 page) | 3 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 5 | (2023 page) | 3 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 6 | (2023 page) | 4 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 7 | (2023 page) | 4 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 8 | (2022 page) | 4 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 9 | (2023 page) | 5 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 10 | (2019 page) | 5 | Good | PM2.5 — fine particulate matter (PM2.5) |
Right now in Billings
The latest EPA AirNow observation puts Billings's AQI at 21 (O3). The days above are historical records, 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.