Metro area air quality · 2025
Evanston, WY
Median AQI 9 (Good). 100.0% of monitored days rated Good across this metro's EPA monitoring network.
- 9
- Median AQI
- 100.0%
- Good-air days
- 0
- Unhealthy days
- 99%
- Cleaner than US metros
Evanston, WY posted a 2025 median AQI of 9 (Good) with 100.0% Good days
According to the U.S. EPA Air Quality System, the Evanston, WY CBSA recorded a median AQI of 9 across 269 monitored days in 2025, with 100.0% rated Good and 0 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 Evanston, WY CBSA's 100.0% Good-day share places it cleaner than 99% of US metros in 2025.
- Closest median-AQI peer
- Mayaguez, PR (97.8% Good, median AQI 9) is the closest nationwide median-AQI peer to Evanston, WY.
- 2020–2025 Good-day shift
- Evanston, WY's Good-day share moved +11.3 points from 2020 to 2025 (median AQI -31).
- Median AQI
- Median AQI: 9
Aggregated from EPA Air Quality System (2025), 269 monitored days. EPA AQS →
The verdict
The Evanston, WY metro runs good on the EPA scale, among the cleanest 10% of US metros, a median AQI of 9 with 100.0% of 269 monitored days in the Good band.
- 9
- median AQI · Good
- 100.0%
- days rated Good
- 99%
- cleaner than US metros
- 50
- worst single reading
No day crossed into the Unhealthy tier across the metro's monitors in 2025.
Insights: Evanston, WY metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 9 over 269 measured days in 2025, which corresponds to a Good band and a Excellent metro-wide health grade. The monitored-day split lands at 269 Good days (100%), 0 Moderate (0%), and 0 Unhealthy-for-Sensitive-Groups (0%). The 90th-percentile AQI finished at 19 while the highest single-day reading hit 50 (Good). Metro residents averaged roughly 30.0 clean-air days per 30-day window across the reporting year.
Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +11.3 points (measured against 364 monitored days in 2020 and 269 in 2025, so raw day counts are not comparable) and the median AQI moved -31 points, which classifies the multi-year trajectory as improving. The metro recorded no Unhealthy-tier days in this annual dataset. Metros with comparable AQI profiles include Mayaguez, PR (97.8% good, AQI 9); Santa Rosa, CA (100.0% good, AQI 9); Bozeman, MT (98.1% good, AQI 11).
Air Quality Summary
Median AQI
9
Good
Good Days
100.0%
269 of 269 days
Max AQI
50
Good
Health Grade
Excellent
90th pct: 19
AQI Day Breakdown (2025)
Distribution of 269 monitored days across EPA AQI categories.
Good
269
100%
Moderate
0
0%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Health Impact Assessment
The Evanston, WY metro area's air quality is rated Excellent based on 100.0% good air days. No unhealthy air days were recorded in 2025.
Air quality is generally acceptable. Unusually sensitive people should monitor real-time conditions at AirNow.gov during high-pollution events.
How does the Evanston, WY metro compare?
How Evanston, WY compares
5-Year Air Quality Trend
Air quality is improving in the Evanston, WY metro. Highest Good-day share: 2025 (100.0%, 269 of 269 monitored days).
| Year | Good | Moderate | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|
| 2020 | 323 | 41 | 0 | 40 | 122 |
| 2021 | 361 | 3 | 0 | 7 | 60 |
| 2022 | 363 | 2 | 0 | 7 | 55 |
| 2023 | 365 | 0 | 0 | 6 | 32 |
| 2024 | 297 | 0 | 0 | 7 | 44 |
| 2025 | 269 | 0 | 0 | 9 | 50 |
Metros with a similar median AQI
CBSA peers nationwide whose annual median AQI sits near Evanston, WY (9).
Mayaguez, PR
Median AQI 9 · 97.8% Good-day share
Santa Rosa, CA
Median AQI 9 · 100.0% Good-day share
Bozeman, MT
Median AQI 11 · 98.1% Good-day share
Show Low, AZ
Median AQI 13 · 99.5% Good-day share
Havre, MT
Median AQI 14 · 92.1% Good-day share
Ponce, PR
Median AQI 3 · 91.4% Good-day share
Metros with similar unhealthy-day exposure
A second relationship type: metros whose unhealthy-or-worse day count is closest to Evanston, WY's 0 (independent of median AQI).
Aberdeen, SD
0 unhealthy-or-worse days · median AQI 27
Aberdeen, WA
0 unhealthy-or-worse days · median AQI 22
Adrian, MI
0 unhealthy-or-worse days · median AQI 41
Akron, OH
0 unhealthy-or-worse days · median AQI 45
Albany, GA
0 unhealthy-or-worse days · median AQI 46
Albany, OR
0 unhealthy-or-worse days · median AQI 27
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 Evanston, WY metro area? ▼
How many unhealthy air days does Evanston, WY have? ▼
Is air quality in Evanston, WY getting better or worse? ▼
What does AQI 9 mean for health? ▼
What is the 90th percentile AQI for Evanston, WY? ▼
How does Evanston, WY compare to other metro areas? ▼
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
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Every figure on PlainAirData 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.