What Is the Air Quality in Twin Falls, Idaho?
Twin Falls, Idaho has an Air Quality Grade of B (good) with a 5-year median AQI of 27. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been improving over the past decade.
Twin Falls, Idaho Air Quality Snapshot
| Air Quality Grade | B76/100 |
| 5-Year Median AQI | 27 (Good) |
| Most Recent Median AQI (2023) | 25 (Good) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Improving (-0.87 AQI/yr) |
| Unhealthy Days (last 5 yr) | 16 |
| National Rank (cleanest = #1) | #100 of 1,020 (10th cleanest percentile) |
| Idaho Rank | #6 of 20 |
What Does the B Grade Mean?
Twin Falls, Idaho earns a B — air quality is reliably in the safe range for most residents most of the time, with a 5-year median AQI of 27. Sensitive groups will see occasional caution days, but the typical resident will not need to change behavior based on air quality.
Twin Falls, Idaho's 5-year median AQI of 27 is 14 points below the national average of 41 — meaningfully cleaner than the typical U.S. metro tracked here. Within Idaho, Twin Falls, Idaho runs cleaner than the state average of 33 — a positive signal that local conditions (terrain, wind patterns, emission sources) are working in residents' favor.
For context within Idaho: Custer, Idaho currently holds the state's cleanest grade (A, AQI 8), while Valley, Idaho sits at the bottom (D, AQI 37).
What's in Twin Falls, Idaho's Air?
The dominant pollutant in Twin Falls, Idaho 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) | 344 | 100% |
Is the Air Getting Better or Worse?
Air quality in Twin Falls, Idaho has been improving over the past decade, with median AQI dropping by roughly 0.9 points per year. That is consistent with the broader national pattern — most U.S. metros have seen steady reductions in particulate and ozone pollution since the 2010s as cleaner vehicles and power plants come online.
In 2015, Twin Falls, Idaho posted a median AQI of 32. By 2023 that figure was 25 — a drop of 7 AQI points cleaner across 9 years of EPA records.
Year-by-Year AQI in Twin Falls, Idaho
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2015 | 32 | 237 | 3 | PM2.5 |
| 2016 | 22 | 333 | 0 | PM2.5 |
| 2017 | 46 | 168 | 6 | PM2.5 |
| 2018 | 39 | 271 | 5 | PM2.5 |
| 2019 | 26 | 344 | 0 | PM2.5 |
| 2020 | 24 | 313 | 7 | PM2.5 |
| 2021 | 28 | 298 | 7 | PM2.5 |
| 2022 | 31 | 280 | 2 | PM2.5 |
| 2023 | 25 | 328 | 0 | PM2.5 |
Health Context for Twin Falls, Idaho
Across the past five years, this area has logged just 16 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 3 days per year, or roughly one every other month. That is a low count by national standards.
For most healthy adults, current air quality in this area does not require any change in behavior. People with severe asthma, COPD, or recent cardiac events should still keep an eye on daily AQI alerts, especially during wildfire 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.
Twin Falls, Idaho has an Air Quality Grade of B (good) with a 5-year median AQI of 27. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been improving 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.