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

Evanston, WY sits in the upper Good-day tercile among EPA CBSA metros on this site (100.0% of 269 monitored days). On the EPA scale the metro runs good, among the cleanest 10% of US metros, with a median AQI of 9 and 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.

Evanston, WY sits in the upper Good-day tercile among EPA CBSA metros on this site (100.0% of 269 monitored days). Signature read: 100.0% Good-day share (high tercile vs CBSA corpus). Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 9 over 269 measured days in 2025 (Good / Excellent). The monitored-day split lands at 269 Good (100%), 0 Moderate (0%), and 0 Unhealthy-for-Sensitive-Groups (0%). The 90th-percentile AQI finished at 19; the highest single-day reading hit 50 (Good).

Across 2020–2025, Good-day share shifted +11.3 points and median AQI moved -31 (improving). No Unhealthy-tier days appear 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).

Best and worst city air quality →

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

Excellent

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

Good-day share better than typical
Evanston, WY 100.0%
Mayaguez, PR 97.8%
Typical US metro 70.6%
Median AQI better than typical
Evanston, WY 9
Mayaguez, PR 9
Typical US metro 41
Unhealthy days / yr better than typical
Evanston, WY 0
Mayaguez, PR 2
Typical US metro 1

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
2020 323 41 0 40
2021 361 3 0 7
2022 363 2 0 7
2023 365 0 0 6
2024 297 0 0 7
2025 269 0 0 9

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

9

Santa Rosa, CA

Median AQI 9 · 100.0% Good-day share

9

Bozeman, MT

Median AQI 11 · 98.1% Good-day share

11

Show Low, AZ

Median AQI 13 · 99.5% Good-day share

13

Havre, MT

Median AQI 14 · 92.1% Good-day share

14

Ponce, PR

Median AQI 3 · 91.4% Good-day share

3

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

27

Aberdeen, WA

0 unhealthy-or-worse days · median AQI 22

22

Adrian, MI

0 unhealthy-or-worse days · median AQI 41

41

Akron, OH

0 unhealthy-or-worse days · median AQI 45

45

Albany, GA

0 unhealthy-or-worse days · median AQI 46

46

Albany, OR

0 unhealthy-or-worse days · median AQI 27

27

Frequently Asked Questions

How many unhealthy air days does Evanston, WY have? ▼
In 2025, the Evanston, WY metro area recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 50.
What is the air quality in the Evanston, WY metro area? ▼
The Evanston, WY metro area has a median Air Quality Index (AQI) of 9, rated "Good." 100.0% of monitored days (269 out of 269) had good air quality in 2025.
Is air quality in Evanston, WY getting better or worse? ▼
Air quality in the Evanston, WY metro is improving across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2025 at 100.0% (269 of 269 days). Lowest qualifying Good-day share: 2020 at 88.7% (323 of 364 days).
What does AQI 9 mean for health? ▼
An AQI of 9 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 Evanston, WY compare to other metro areas? ▼
The Evanston, WY metro has 100.0% good air days. Similar metros: Mayaguez, PR (97.8% good), Santa Rosa, CA (100.0% good), Bozeman, MT (98.1% good).
What is the 90th percentile AQI for Evanston, WY? ▼
The 90th percentile AQI for the Evanston, WY metro area is 19, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 50 (Good).

Data Sources

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