Metro area air quality · 2025

Lewiston, ID-WA

Median AQI 43 (Good). 60.0% of monitored days rated Good across this metro's EPA monitoring network.

43
Median AQI
60.0%
Good-air days
2
Unhealthy days
25%
Cleaner than US metros

Lewiston, ID-WA posted a 2025 median AQI of 43 (Good) with 60.0% Good days

According to the U.S. EPA Air Quality System, the Lewiston, ID-WA CBSA recorded a median AQI of 43 across 365 monitored days in 2025, with 60.0% rated Good and 2 unhealthy or worse. This is an annual metro comparison, not a live advisory.

Data source EPA Air Quality System (AQS)

Cleaner than US metros
The Lewiston, ID-WA CBSA's 60.0% Good-day share places it cleaner than 25% of US metros in 2025.
Closest median-AQI peer
Ashtabula, OH (81.2% Good, median AQI 43) is the closest nationwide median-AQI peer to Lewiston, ID-WA.
2020–2025 Good-day shift
Lewiston, ID-WA's Good-day share moved -6.3 points from 2020 to 2025 (median AQI +3).
Median AQI
Median AQI: 43

Aggregated from EPA Air Quality System (2025), 365 monitored days. EPA AQS →

The verdict

Lewiston, ID-WA lands in the lower Good-day tercile (60.0% Good), a thinner clean-air share than most CBSA peers here. On the EPA scale the metro runs good, more polluted than the median US metro, with a median AQI of 43 and 60.0% of 365 monitored days in the Good band.

43
median AQI · Good
60.0%
days rated Good
25%
cleaner than US metros
161
worst single reading

2 days reached Unhealthy or worse across the metro's monitors in 2025.

Annual release change

What changed in the 2025 EPA annual release

2024 → 2025
  • Lewiston, ID-WA metro's peak single-day AQI fell from 196 to 161 between the 2024 and 2025 EPA annual releases, a change of -35 points.
  • Lewiston, ID-WA metro's Unhealthy-category days fell from 4 to 2 between the 2024 and 2025 EPA annual releases, a change of -2 days.
  • Lewiston, ID-WA metro's Good-day share fell from 61.9% to 60.3% between the 2024 and 2025 EPA annual releases, a change of -1.5 percentage points.

Compared against 362 monitored days in 2024 and 363 in 2025. These are arithmetic differences between two stored EPA annual summaries, not a cause claim or a live advisory.

National release changes Two-year CSV

Lewiston, ID-WA lands in the lower Good-day tercile (60.0% Good), a thinner clean-air share than most CBSA peers here. Signature read: 60.0% Good-day share (low tercile vs CBSA corpus). Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 43 over 365 measured days in 2025 (Good / Moderate). The monitored-day split lands at 219 Good (60%), 142 Moderate (39%), and 2 Unhealthy-for-Sensitive-Groups (1%). The 90th-percentile AQI finished at 68; the highest single-day reading hit 161 (Unhealthy).

Across 2020–2025, Good-day share shifted -6.3 points and median AQI moved +3 (worsening). The annual record contains 2 days at Unhealthy or worse. Metros with comparable AQI profiles include Ashtabula, OH (81.2% good, AQI 43); Bloomington, IN (67.7% good, AQI 43); Champaign-Urbana, IL (65.8% good, AQI 43).

Health effects of air pollution →

Air Quality Summary

Median AQI

43

Good

Good Days

60.0%

219 of 365 days

Max AQI

161

Unhealthy

Health Grade

Moderate

90th pct: 68

AQI Day Breakdown (2025)

Distribution of 365 monitored days across EPA AQI categories.

Good

219

60%

Moderate

142

39%

USG

2

1%

Unhealthy

2

1%

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 60.0% good air days. There were 2 unhealthy days in 2025 when outdoor activity should be limited.

Air quality is acceptable most days, but 2 days reached "Unhealthy for Sensitive Groups" and peak AQI reached 161. 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 worse than typical
Lewiston, ID-WA 60.0%
Ashtabula, OH 81.2%
Typical US metro 70.6%
Median AQI worse than typical
Lewiston, ID-WA 43
Ashtabula, OH 43
Typical US metro 41
Unhealthy days / yr worse than typical
Lewiston, ID-WA 2
Ashtabula, OH 0
Typical US metro 1

5-Year Air Quality Trend

Air quality is worsening in the Lewiston, ID-WA metro. Highest Good-day share: 2020 (66.7%, 236 of 354 monitored 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 219 142 2 43

Metros with a similar median AQI

CBSA peers nationwide whose annual median AQI sits near Lewiston, ID-WA (43).

Ashtabula, OH

Median AQI 43 · 81.2% Good-day share

43

Bloomington, IN

Median AQI 43 · 67.7% Good-day share

43

Champaign-Urbana, IL

Median AQI 43 · 65.8% Good-day share

43

Cleveland, MS

Median AQI 43 · 71.9% Good-day share

43

Columbus, IN

Median AQI 43 · 72.6% Good-day share

43

Durham-Chapel Hill, NC

Median AQI 43 · 71.5% Good-day share

43

Metros with similar unhealthy-day exposure

A second relationship type: metros whose unhealthy-or-worse day count is closest to Lewiston, ID-WA's 2 (independent of median AQI).

Ardmore, OK

2 unhealthy-or-worse days · median AQI 45

45

Bridgeport-Stamford-Norwalk, CT

2 unhealthy-or-worse days · median AQI 44

44

Chattanooga, TN-GA

2 unhealthy-or-worse days · median AQI 49

49

Cincinnati, OH-KY-IN

2 unhealthy-or-worse days · median AQI 56

56

Columbus, GA-AL

2 unhealthy-or-worse days · median AQI 48

48

Davenport-Moline-Rock Island, IA-IL

2 unhealthy-or-worse days · median AQI 46

46

Frequently Asked Questions

How many unhealthy air days does Lewiston, ID-WA have? ▼
In 2025, the Lewiston, ID-WA metro area recorded 2 unhealthy air days (2 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 161.
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 43, rated "Good." 60.0% of monitored days (219 out of 365) had good air quality in 2025.
Is air quality in Lewiston, ID-WA getting better or worse? ▼
Air quality in the Lewiston, ID-WA metro is worsening across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2020 at 66.7% (236 of 354 days). Lowest qualifying Good-day share: 2023 at 52.1% (187 of 359 days).
What does AQI 43 mean for health? ▼
An AQI of 43 is "Good", air quality is satisfactory and poses little or no health risk. This is the best category on the EPA's AQI scale.
How does Lewiston, ID-WA compare to other metro areas? ▼
The Lewiston, ID-WA metro has 60.0% good air days. Similar metros: Ashtabula, OH (81.2% good), Bloomington, IN (67.7% good), Champaign-Urbana, IL (65.8% good).
What is the 90th percentile AQI for Lewiston, ID-WA? ▼
The 90th percentile AQI for the Lewiston, ID-WA metro area is 68, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 161 (Unhealthy).

Data Sources

Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by CBSA dataset for Lewiston, ID-WA, 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, Lewiston, ID-WA · 2020–2025