What Is the Air Quality in Asotin, Washington?
Asotin, Washington has an Air Quality Grade of D (poor) with a 5-year median AQI of 43. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been worsening over the past decade.
Asotin, Washington Air Quality Snapshot
| Air Quality Grade | D47/100 |
| 5-Year Median AQI | 43 (Good) |
| Most Recent Median AQI (2023) | 49 (Good) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Worsening (+1.64 AQI/yr) |
| Unhealthy Days (last 5 yr) | 42 |
| National Rank (cleanest = #1) | #669 of 1,020 (66th most polluted percentile) |
| Washington Rank | #27 of 30 |
What Does the D Grade Mean?
Asotin, Washington earns a D — air quality falls below the U.S. average, with a 5-year median AQI of 43. Residents with asthma, COPD, heart disease, or young children should watch daily AQI forecasts and limit outdoor exertion when alerts go out.
Asotin, Washington's 5-year median AQI of 43 is 2 points above the national average of 41 — meaningfully more polluted than the typical U.S. metro tracked here. Within Washington, Asotin, Washington 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 Washington: Garfield, Washington currently holds the state's cleanest grade (A, AQI 20), while Yakima, Washington sits at the bottom (C, AQI 49).
What's in Asotin, Washington's Air?
The dominant pollutant in Asotin, Washington 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) | 359 | 100% |
Is the Air Getting Better or Worse?
Air quality in Asotin, Washington has been getting worse over the past decade, with median AQI climbing by roughly 1.6 points per year. That bucks the national trend of broad improvement, and most often reflects either growing wildfire smoke exposure (particularly across the West) or rising local emissions from population and freight growth.
In 2014, Asotin, Washington posted a median AQI of 33. By 2023 that figure was 49 — a rise of 16 AQI points dirtier across 10 years of EPA records.
Year-by-Year AQI in Asotin, Washington
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 33 | 221 | 3 | PM2.5 |
| 2015 | 36 | 177 | 0 | PM2.5 |
| 2016 | 36 | 280 | 0 | PM2.5 |
| 2017 | 39 | 226 | 19 | PM2.5 |
| 2018 | 36 | 214 | 8 | PM2.5 |
| 2019 | 36 | 250 | 1 | PM2.5 |
| 2020 | 38 | 229 | 9 | PM2.5 |
| 2021 | 48 | 176 | 19 | PM2.5 |
| 2022 | 46 | 195 | 7 | PM2.5 |
| 2023 | 49 | 184 | 6 | PM2.5 |
Health Context for Asotin, Washington
Across the past five years, this area has logged 42 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 8 days per year. That is roughly typical for a U.S. metro, with most caution days clustered in summer (ozone) or wildfire season.
Treat daily AQI forecasts as essential input. On flagged days, sensitive groups (asthma, COPD, heart disease, pregnancy, young children, older adults) should limit outdoor exertion and keep windows closed. A HEPA air cleaner sized to a bedroom or family room can cut indoor PM2.5 by 80%+ during smoke or pollution events. 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.
Asotin, Washington has an Air Quality Grade of D (poor) with a 5-year median AQI of 43. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been worsening 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.
For readers turning this answer into action: cross-reference against the underlying the EPA Air Quality System (AQS) record before acting on time-sensitive decisions. The site renders the data as it was published; subsequent revisions can shift the picture, and the live federal data is always the authoritative current reference.
Source: EPA Outdoor Air Quality Data, 2026.