Metro area air quality · 2025

Lewiston, ID-WA

Median AQI 38 (Good). 72.2% of monitored days rated Good across this metro's EPA monitoring network.

38
Median AQI
72.2%
Good-air days
1
Unhealthy days
48%
Cleaner than US metros

Aggregated from EPA Air Quality System (2025), 241 monitored days. EPA AQS →

The verdict

The Lewiston, ID-WA metro runs good on the EPA scale, more polluted than the median US metro, a median AQI of 38 with 72.2% of 241 monitored days in the Good band.

38
median AQI · Good
72.2%
days rated Good
48%
cleaner than US metros
151
worst single reading

1 day reached Unhealthy or worse across the metro's monitors in 2025.

Insights: Lewiston, ID-WA metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 38 over 241 measured days in 2025, which corresponds to a Good band and a Moderate metro-wide health grade. The monitored-day split lands at 174 Good days (72%), 65 Moderate (27%), and 1 Unhealthy-for-Sensitive-Groups (0%). The 90th-percentile AQI finished at 65 while the highest single-day reading hit 151 (Unhealthy). Metro residents averaged roughly 21.7 clean-air days per 30-day window across the reporting year.

Across the 2020–2025 trend window, good days shifted by -62 and the median AQI moved -2 points, which classifies the multi-year trajectory as improving. The metro recorded 1 unhealthy-or-worse days combined, on those days the EPA recommends that sensitive groups limit prolonged outdoor exertion, and many schools and athletic programs adjust outdoor activity accordingly. Metros with comparable AQI profiles include Appleton, WI (78.5% good, AQI 38); Atlantic City-Hammonton, NJ (79.6% good, AQI 38); Barnstable Town, MA (92.5% good, AQI 38).

Air Quality Summary

Median AQI

38

Good

Good Days

72.2%

174 of 241 days

Max AQI

151

Unhealthy

Health Grade

Moderate

90th pct: 65

AQI Day Breakdown (2025)

Distribution of 241 monitored days across EPA AQI categories.

Good

174

72%

Moderate

65

27%

USG

1

0%

Unhealthy

1

0%

Very Unhealthy

0

0%

Hazardous

0

0%

Health Impact Assessment

Moderate

The Lewiston, ID-WA metro area's air quality is rated Moderate based on 72.2% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.

Air quality is acceptable most days, but 1 days reached "Unhealthy for Sensitive Groups" and peak AQI reached 151. Sensitive groups should monitor real-time conditions at AirNow.gov.

How does the Lewiston, ID-WA metro compare?

How Lewiston, ID-WA compares

Good-day share better than US avg
Lewiston, ID-WA 72.2%
Appleton, WI 78.5%
US average 71.3%
Median AQI better than US avg
Lewiston, ID-WA 38
Appleton, WI 38
US average 41
Unhealthy days / yr about average
Lewiston, ID-WA 1
Appleton, WI 1
US average 1

5-Year Air Quality Trend

Air quality is improving in the Lewiston, ID-WA metro. Best year: 2020 (236 good days).

Year Good Moderate Unhealthy Median AQI
2020 236 118 0 40
2021 201 145 4 46
2022 196 162 4 47
2023 187 171 1 49
2024 224 134 4 43
2025 174 65 1 38

Metros with Similar Air Quality

Metro areas across the US with a similar median AQI to Lewiston, ID-WA.

Appleton, WI

AQI 38 · 78.5% good

38

Atlantic City-Hammonton, NJ

AQI 38 · 79.6% good

38

Barnstable Town, MA

AQI 38 · 92.5% good

38

Bay City, MI

AQI 38 · 71.8% good

38

Cadillac, MI

AQI 38 · 89.5% good

38

Claremont-Lebanon, NH-VT

AQI 38 · 81.3% good

38

More Air Quality Data

Explore EPA air quality rankings and guides across U.S. metros and counties.

Cleanest Metro Areas

U.S. metros ranked by their share of Good air-quality days.

Worst Air Quality

Counties and metros with the most unhealthy air days.

All Metro Areas

Annual AQI by CBSA for every monitored U.S. metro area.

Best and Worst City Air

What drives urban air quality and how metro areas compare.

Air Quality Guides

Frequently Asked Questions

What is the air quality in the Lewiston, ID-WA metro area? ▼
The Lewiston, ID-WA metro area has a median Air Quality Index (AQI) of 38, rated "Good." 72.2% of monitored days (174 out of 241) had good air quality in 2025.
How many unhealthy air days does Lewiston, ID-WA have? ▼
In 2025, the Lewiston, ID-WA metro area recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 151.
Is air quality in Lewiston, ID-WA getting better or worse? ▼
Air quality in the Lewiston, ID-WA metro is improving based on 5-year trends (2020-2025). Best year: 2020 with 236 good days. Worst year: 2025 with 174 good days.
What does AQI 38 mean for health? ▼
An AQI of 38 is "Good", air quality is satisfactory and poses little or no health risk. This is the best category on the EPA's AQI scale.
What is the 90th percentile AQI for Lewiston, ID-WA? ▼
The 90th percentile AQI for the Lewiston, ID-WA metro area is 65, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 151 (Unhealthy).
How does Lewiston, ID-WA compare to other metro areas? ▼
The Lewiston, ID-WA metro has 72.2% good air days. Similar metros: Appleton, WI (78.5% good), Atlantic City-Hammonton, NJ (79.6% good), Barnstable Town, MA (92.5% good).

Data Sources

Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by CBSA dataset, 2020–2025. See our methodology for how AQI, median, and coverage figures are computed.

Read our methodology , how this data is sourced, computed, and verified.

Source: U.S. EPA Air Quality System (AQS) Annual AQI by CBSA summary files (metro-level) · 2020–2025

Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.