Lewis, Washington Air Quality
Lewis County, Washington (WA)
↓ Improvingover 10 years
How Lewis, Washington Air Quality Compares
Lewis, Washington's median AQI of 25is 39% better than the national average of 41. Air quality has improved by 6 AQI points over the past decade. The area averages 3 unhealthy air days per year. The primary pollutant of concern is Fine Particulate Matter (PM2.5).
10-Year AQI Trend
The solid line shows the median AQI each year. The dashed line shows the 90th percentile (worst 10% of days). This area has seen measurable air quality improvement over the decade.
Air Quality Day Breakdown
Number of days per year in each EPA AQI category. Green = Good (AQI 0-50), Yellow = Moderate (51-100), Orange = Unhealthy for Sensitive Groups (101-150), Red = Unhealthy or worse (151+).
Year-by-Year Data
| Year | Median AQI | 90th Pct | Max AQI | Good Days | Moderate | Unhealthy+ | Pollutant |
|---|---|---|---|---|---|---|---|
| 2023 | 25 | 54 | 159 | 314 | 46 | 2 | PM2.5 |
| 2022 | 26 | 66 | 198 | 285 | 70 | 10 | PM2.5 |
| 2021 | 23 | 46 | 71 | 328 | 22 | 0 | PM2.5 |
| 2020 | 25 | 46 | 258 | 314 | 20 | 1 | PM2.5 |
| 2019 | 27 | 54 | 66 | 308 | 57 | 0 | PM2.5 |
| 2018 | 28 | 58 | 172 | 298 | 61 | 6 | PM2.5 |
| 2017 | 26 | 57 | 162 | 302 | 60 | 3 | PM2.5 |
| 2016 | 26 | 44 | 70 | 340 | 26 | 0 | PM2.5 |
| 2015 | 30 | 53 | 154 | 311 | 49 | 1 | PM2.5 |
| 2014 | 31 | 54 | 78 | 312 | 53 | 0 | PM2.5 |
What This Means for Lewis County Residents
Lewis, Washington has received an Air Quality Grade of B (75/100) based on a decade of monitoring data from the EPA's air quality monitoring program. The current median AQI of 25 falls in the "Good" range.
Encouragingly, air quality here has been improving, with the median AQI dropping by 6 points over the monitoring period. This trend suggests continued investment in emission controls and cleaner energy.
The primary pollutant affecting this area is Fine Particulate Matter (PM2.5). Over the past 5 years, this area has averaged 3 unhealthy air quality days per year, days when sensitive groups (children, elderly, those with respiratory conditions) should limit outdoor activity. The American Lung Association's State of the Air report provides additional context on long-term health risks from air pollution exposure.
Related Cities in Washington
Frequently Asked Questions
Lewis, Washington has a current median AQI of 25, which falls in the "Good" range. The area has received an Air Quality Grade of B (75/100) based on 10 years of EPA monitoring data.
Air quality in Lewis, Washington is improving over the past decade. The median AQI has changed by -6 points from 2014 to 2023.
Lewis, Washington averages 3 unhealthy air quality days per year over the past 5 years. On these days, sensitive groups including children, the elderly, and those with respiratory conditions should limit outdoor activity.
The primary pollutant affecting Lewis, Washington is Fine Particulate Matter (PM2.5). This is the dominant contributor to elevated AQI readings in the Lewis County area.
Lewis, Washington averages 3 unhealthy air days per year. This is relatively low, making it a reasonable choice for asthma sufferers. The primary pollutant is Fine Particulate Matter (PM2.5), which is a known asthma trigger.
With a median AQI of 25 (Good), outdoor exercise in Lewis, Washington is generally safe year-round. Lewis, Washington averages 3 days per year when athletes should move workouts indoors.
this entity is one of the data points covered by this site’s U.S. air quality and pollution monitoring dataset. The detail above comes directly from the EPA Air Quality System (AQS); the context that follows situates the headline numbers against the broader distribution across U.S. counties and states.
The methodology behind every numeric value on this page is publicly documented on the the EPA Air Quality System (AQS) portal and described in detail on this site’s methodology page. Refresh cadence varies by underlying series; the page surfaces the as-of date for each number so readers can trace any figure back to the source release.
For readers using this page as a decision input, the related-entity pages elsewhere on the site provide the comparison set. The most useful comparison for this entity is typically a peer within U.S. counties and states with similar size, similar exposure, or similar geography — not the national-level summary alone.