Metro area air quality · 2025
Mount Vernon, IL
Median AQI 42 (Good). 67.9% of monitored days rated Good across this metro's EPA monitoring network.
- 42
- Median AQI
- 67.9%
- Good-air days
- 0
- Unhealthy days
- 40%
- Cleaner than US metros
Mount Vernon, IL posted a 2025 median AQI of 42 (Good) with 67.9% Good days
According to the U.S. EPA Air Quality System, the Mount Vernon, IL CBSA recorded a median AQI of 42 across 361 monitored days in 2025, with 67.9% 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 Mount Vernon, IL CBSA's 67.9% Good-day share places it cleaner than 40% of US metros in 2025.
- Closest median-AQI peer
- Allentown-Bethlehem-Easton, PA-NJ (66.8% Good, median AQI 42) is the closest nationwide median-AQI peer to Mount Vernon, IL.
- 2020–2025 Good-day shift
- Mount Vernon, IL's Good-day share moved +4.5 points from 2020 to 2025 (median AQI -4).
- Median AQI
- Median AQI: 42
Aggregated from EPA Air Quality System (2025), 361 monitored days. EPA AQS →
The verdict
The Mount Vernon, IL metro runs good on the EPA scale, more polluted than the median US metro, a median AQI of 42 with 67.9% of 361 monitored days in the Good band.
- 42
- median AQI · Good
- 67.9%
- days rated Good
- 40%
- cleaner than US metros
- 98
- worst single reading
No day crossed into the Unhealthy tier across the metro's monitors in 2025.
Annual release change
What changed in the 2025 EPA annual release
- Mount Vernon, IL metro's Good-day share rose from 64.7% to 67.9% between the 2024 and 2025 EPA annual releases, a change of +3.2 percentage points.
- Mount Vernon, IL metro's peak single-day AQI fell from 112 to 98 between the 2024 and 2025 EPA annual releases, a change of -14 points.
Insights: Mount Vernon, IL metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 42 over 361 measured days in 2025, which corresponds to a Good band and a Moderate metro-wide health grade. The monitored-day split lands at 245 Good days (68%), 116 Moderate (32%), and 0 Unhealthy-for-Sensitive-Groups (0%). The 90th-percentile AQI finished at 61 while the highest single-day reading hit 98 (Moderate). Metro residents averaged roughly 20.4 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 +4.5 points and the median AQI moved -4 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 Allentown-Bethlehem-Easton, PA-NJ (66.8% good, AQI 42); Amarillo, TX (78.4% good, AQI 42); Carson City, NV (86.2% good, AQI 42).
Air Quality Summary
Median AQI
42
Good
Good Days
67.9%
245 of 361 days
Max AQI
98
Moderate
Health Grade
Moderate
90th pct: 61
AQI Day Breakdown (2025)
Distribution of 361 monitored days across EPA AQI categories.
Good
245
68%
Moderate
116
32%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Health Impact Assessment
The Mount Vernon, IL metro area's air quality is rated Moderate based on 67.9% 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 Mount Vernon, IL metro compare?
How Mount Vernon, IL compares
5-Year Air Quality Trend
Air quality is improving in the Mount Vernon, IL metro. Highest Good-day share: 2025 (67.9%, 245 of 361 monitored days).
| Year | Good | Moderate | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|
| 2020 | 223 | 129 | 0 | 46 | 118 |
| 2021 | 207 | 155 | 0 | 48 | 115 |
| 2022 | 227 | 138 | 0 | 45 | 88 |
| 2023 | 213 | 141 | 1 | 46 | 157 |
| 2024 | 236 | 129 | 0 | 44 | 112 |
| 2025 | 245 | 116 | 0 | 42 | 98 |
Metros with a similar median AQI
CBSA peers nationwide whose annual median AQI sits near Mount Vernon, IL (42).
Allentown-Bethlehem-Easton, PA-NJ
Median AQI 42 · 66.8% Good-day share
Amarillo, TX
Median AQI 42 · 78.4% Good-day share
Carson City, NV
Median AQI 42 · 86.2% Good-day share
Casper, WY
Median AQI 42 · 86.3% Good-day share
Clarksville, TN-KY
Median AQI 42 · 72.0% Good-day share
Daphne-Fairhope-Foley, AL
Median AQI 42 · 75.5% Good-day share
Metros with similar unhealthy-day exposure
A second relationship type: metros whose unhealthy-or-worse day count is closest to Mount Vernon, IL'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 Mount Vernon, IL metro area? ▼
How many unhealthy air days does Mount Vernon, IL have? ▼
Is air quality in Mount Vernon, IL getting better or worse? ▼
What does AQI 42 mean for health? ▼
What is the 90th percentile AQI for Mount Vernon, IL? ▼
How does Mount Vernon, IL 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.