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

The Bay City, MI metro runs good on the EPA scale, more polluted than the median US metro, a median AQI of 39 with 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

2024 → 2025
  • 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.

Compared against 363 monitored days in 2024 and 355 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

Insights: Bay City, MI metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 39 over 358 measured days in 2025, which corresponds to a Good band and a Moderate metro-wide health grade. The monitored-day split lands at 252 Good days (70%), 103 Moderate (29%), and 3 Unhealthy-for-Sensitive-Groups (1%). The 90th-percentile AQI finished at 60 while the highest single-day reading hit 139 (USG). Metro residents averaged roughly 21.1 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 -18.1 points and the median AQI moved +17 points, which classifies the multi-year trajectory as worsening. The metro recorded no Unhealthy-tier days 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

Moderate

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

Good-day share about typical
Bay City, MI 70.4%
Brainerd, MN 74.3%
Typical US metro 70.6%
Median AQI better than typical
Bay City, MI 39
Brainerd, MN 39
Typical US metro 41
Unhealthy days / yr better than typical
Bay City, MI 0
Brainerd, MN 8
Typical US metro 1

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
2020 325 40 0 22
2021 290 73 0 28
2022 287 67 0 32
2023 229 128 3 42
2024 277 86 0 37
2025 252 103 0 39

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

39

Cambridge, MD

Median AQI 39 · 86.0% Good-day share

39

Charleston, WV

Median AQI 39 · 77.0% Good-day share

39

Dalton, GA

Median AQI 39 · 90.3% Good-day share

39

Harrisonburg, VA

Median AQI 39 · 80.0% Good-day share

39

Indiana, PA

Median AQI 39 · 74.8% Good-day share

39

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

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

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 Bay City, MI metro area? ▼
The Bay City, MI metro area has a median Air Quality Index (AQI) of 39, rated "Good." 70.4% of monitored days (252 out of 358) had good air quality in 2025.
How many unhealthy air days does Bay City, MI have? ▼
In 2025, the Bay City, MI metro area recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 139.
Is air quality in Bay City, MI getting better or worse? ▼
Air quality in the Bay City, MI 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 89.0% (325 of 365 days). Lowest qualifying Good-day share: 2023 at 63.6% (229 of 360 days).
What does AQI 39 mean for health? ▼
An AQI of 39 is "Good", air quality is satisfactory and poses little or no health risk. This is the best category on the EPA's AQI scale.
What is the 90th percentile AQI for Bay City, MI? ▼
The 90th percentile AQI for the Bay City, MI metro area is 60, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 139 (USG).
How does Bay City, MI compare to other metro areas? ▼
The Bay City, MI metro has 70.4% good air days. Similar metros: Brainerd, MN (74.3% good), Cambridge, MD (86.0% good), Charleston, WV (77.0% good).

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.