What Is the Air Quality in Flathead, Montana?
Flathead, Montana has an Air Quality Grade of C (fair) with a 5-year median AQI of 40. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been stable over the past decade.
Flathead, Montana Air Quality Snapshot
| Air Quality Grade | C63/100 |
| 5-Year Median AQI | 40 (Good) |
| Most Recent Median AQI (2023) | 43 (Good) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Stable (-0.08 AQI/yr) |
| Unhealthy Days (last 5 yr) | 29 |
| National Rank (cleanest = #1) | #472 of 1,020 (46th cleanest percentile) |
| Montana Rank | #15 of 19 |
What Does the C Grade Mean?
Flathead, Montana earns a C — air quality is fair, but not great. With a 5-year median AQI of 40, the city sees a meaningful number of "Moderate" days each year, when the EPA flags air as a concern for unusually sensitive people.
Flathead, Montana's 5-year median AQI of 40 is right around the national average of 41 across the 1,020 monitored U.S. cities tracked here. Within Montana, Flathead, Montana runs more polluted than the state average of 31 — local sources or geography are concentrating pollution above the state's typical reading.
For context within Montana: Rosebud, Montana currently holds the state's cleanest grade (A, AQI 23), while Sanders, Montana sits at the bottom (D, AQI 36).
What's in Flathead, Montana's Air?
The dominant pollutant in Flathead, Montana is Fine Particulate Matter (PM2.5). Fine particulate matter — particles less than 2.5 micrometers across — comes mostly from combustion: vehicle exhaust, wildfire smoke, residential wood burning, and industrial emissions. Because these particles are small enough to enter the bloodstream, PM2.5 is the pollutant most strongly linked to cardiovascular disease, respiratory illness, and premature death.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Fine Particulate Matter (PM2.5) | 213 | 58% |
| Ground-Level Ozone | 135 | 37% |
| Coarse Particulate Matter (PM10) | 17 | 5% |
Is the Air Getting Better or Worse?
Air quality in Flathead, Montana has held roughly steady over the past decade, with year-to-year shifts in median AQI of less than half a point. That stability makes the city's long-run grade a reliable signal of what residents can expect day-to-day.
In 2014, Flathead, Montana posted a median AQI of 41. By 2023 that figure was 43 — a rise of 2 AQI points dirtier across 10 years of EPA records.
Year-by-Year AQI in Flathead, Montana
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 41 | 254 | 2 | PM2.5 |
| 2015 | 44 | 216 | 12 | PM2.5 |
| 2016 | 37 | 298 | 0 | Ozone |
| 2017 | 42 | 250 | 11 | PM2.5 |
| 2018 | 45 | 222 | 16 | PM2.5 |
| 2019 | 39 | 267 | 1 | Ozone |
| 2020 | 37 | 286 | 8 | Ozone |
| 2021 | 39 | 268 | 9 | Ozone |
| 2022 | 41 | 249 | 3 | PM2.5 |
| 2023 | 43 | 237 | 8 | PM2.5 |
Health Context for Flathead, Montana
Across the past five years, this area has logged 29 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 6 days per year. That is roughly typical for a U.S. metro, with most caution days clustered in summer (ozone) or wildfire season.
Healthy adults can continue normal outdoor activity in most weather, but should pay attention to AQI alerts during the worst pollution windows. People with asthma, heart disease, or pregnancy should reduce prolonged or intense outdoor exertion on flagged days, and consider running an indoor HEPA air cleaner during peak season. Because PM2.5 penetrates deep into the lungs and bloodstream, an N95 or KN95 mask provides meaningful protection on smoky or high-particulate days — surgical masks do not.
How This Grade Is Calculated
The AirHistory Air Quality Grade combines four signals: the 5-year median AQI (40% of the score), the 10-year trend direction (30%), the count of unhealthy days per year (20%), and the dominant pollutant type (10%). All four come directly from the EPA Air Quality System (AQS), which aggregates readings from federally certified monitors. Read the full methodology.
Flathead, Montana has an Air Quality Grade of C (fair) with a 5-year median AQI of 40. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been stable over the past decade.
The data source behind this answer is the EPA Air Quality System (AQS). Every figure on the page traces back to that source; the methodology page describes the inputs and the refresh cadence in full detail.
A practical caveat: the headline answer above reflects the most recent the EPA Air Quality System (AQS) vintage; underlying data is often revised for months after first publication, and the right reference for any specific decision is whichever vintage is current at the time of the decision. The as-of date is stamped on every page.
Source: EPA Outdoor Air Quality Data, 2026.