Metro area air quality · 2025
Bay City, MI
Median AQI 39 (Good). 70.4% of monitored days rated Good across this metro's EPA monitoring network.
- 39
- Median AQI
- 70.4%
- Good-air days
- 0
- Unhealthy days
- 47%
- Cleaner than US metros
Bay City, MI posted a 2025 median AQI of 39 (Good) with 70.4% Good days
According to the U.S. EPA Air Quality System, the Bay City, MI CBSA recorded a median AQI of 39 across 358 monitored days in 2025, with 70.4% 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 Bay City, MI CBSA's 70.4% Good-day share places it cleaner than 47% of US metros in 2025.
- Closest median-AQI peer
- Brainerd, MN (74.3% Good, median AQI 39) is the closest nationwide median-AQI peer to Bay City, MI.
- 2020–2025 Good-day shift
- Bay City, MI's Good-day share moved -18.1 points from 2020 to 2025 (median AQI +17).
- Median AQI
- Median AQI: 39
Aggregated from EPA Air Quality System (2025), 358 monitored days. EPA AQS →
The verdict
Bay City, MI's peak reading 139 is in the upper max-AQI tercile among CBSA metros here. On the EPA scale the metro runs good, more polluted than the median US metro, with a median AQI of 39 and 70.4% of 358 monitored days in the Good band.
- 39
- median AQI · Good
- 70.4%
- days rated Good
- 47%
- cleaner than US metros
- 139
- 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
- Bay City, MI metro's peak single-day AQI rose from 73 to 139 between the 2024 and 2025 EPA annual releases, a change of +66 points.
- Bay City, MI metro's Good-day share fell from 76.3% to 71.0% between the 2024 and 2025 EPA annual releases, a change of -5.3 percentage points.
Bay City, MI's peak reading 139 is in the upper max-AQI tercile among CBSA metros here. Signature read: peak AQI 139 (high tercile vs CBSA corpus). Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 39 over 358 measured days in 2025 (Good / Moderate). The monitored-day split lands at 252 Good (70%), 103 Moderate (29%), and 3 Unhealthy-for-Sensitive-Groups (1%). The 90th-percentile AQI finished at 60; the highest single-day reading hit 139 (USG).
Across 2020–2025, Good-day share shifted -18.1 points and median AQI moved +17 (worsening). No Unhealthy-tier days appear in this annual dataset. Metros with comparable AQI profiles include Brainerd, MN (74.3% good, AQI 39); Cambridge, MD (86.0% good, AQI 39); Charleston, WV (77.0% good, AQI 39).
Air Quality Summary
Median AQI
39
Good
Good Days
70.4%
252 of 358 days
Max AQI
139
USG
Health Grade
Moderate
90th pct: 60
AQI Day Breakdown (2025)
Distribution of 358 monitored days across EPA AQI categories.
Good
252
70%
Moderate
103
29%
USG
3
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Health Impact Assessment
The Bay City, MI metro area's air quality is rated Moderate based on 70.4% 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 Bay City, MI metro compare?
How Bay City, MI compares
5-Year Air Quality Trend
Air quality is worsening in the Bay City, MI metro. Highest Good-day share: 2020 (89.0%, 325 of 365 monitored days).
| Year | Good | Moderate | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|
| 2020 | 325 | 40 | 0 | 22 | 77 |
| 2021 | 290 | 73 | 0 | 28 | 86 |
| 2022 | 287 | 67 | 0 | 32 | 85 |
| 2023 | 229 | 128 | 3 | 42 | 192 |
| 2024 | 277 | 86 | 0 | 37 | 73 |
| 2025 | 252 | 103 | 0 | 39 | 139 |
Metros with a similar median AQI
CBSA peers nationwide whose annual median AQI sits near Bay City, MI (39).
Brainerd, MN
Median AQI 39 · 74.3% Good-day share
Cambridge, MD
Median AQI 39 · 86.0% Good-day share
Charleston, WV
Median AQI 39 · 77.0% Good-day share
Dalton, GA
Median AQI 39 · 90.3% Good-day share
Harrisonburg, VA
Median AQI 39 · 80.0% Good-day share
Indiana, PA
Median AQI 39 · 74.8% Good-day share
Metros with similar unhealthy-day exposure
A second relationship type: metros whose unhealthy-or-worse day count is closest to Bay City, MI'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
Frequently Asked Questions
What is the 90th percentile AQI for Bay City, MI? ▼
How many unhealthy air days does Bay City, MI have? ▼
What is the air quality in the Bay City, MI metro area? ▼
Is air quality in Bay City, MI getting better or worse? ▼
What does AQI 39 mean for health? ▼
How does Bay City, MI compare to other metro areas? ▼
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by CBSA dataset for Bay City, MI, 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, Bay City, MI · 2020–2025