Median AQI
38
Good
Michigan · County air quality · 2025
Bay County, Michigan
Median AQI 38 (Good). 71.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 38
- Median AQI
- 71.8%
- Good-air days
- 0
- Unhealthy days
- 35%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Bay County's air is good on balance, more polluted than the median US county, a median AQI of 38 with 71.8% of 181 monitored days in the Good band, driven mainly by PM2.5.
- 38
- median AQI · Good
- 71.8%
- days rated Good
- PM2.5
- main pollutant
- 35%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 99.
Data updated July 2026
- Good · 130 d · 71.8%
- Moderate · 51 d · 28.2%
How did Bay County's air break down in 2025?
Across 181 monitored days, 130 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 99 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 38 (Good).
Insights: Bay County, Michigan. EPA monitors recorded a median Air Quality Index of 38 across 181 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 130 (72%) fell in the Good band (AQI 0–50), 51 (28%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 58, while the worst single-day peak hit 99 (Moderate). Residents averaged about 21.5 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (181 days). Across the 2020–2025 trend window, good days shifted by -195 and the median AQI moved +16 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 99, moderate but never Unhealthy. Nearby counties show comparable readings: Allegan (71.2% good, AQI 43); Benzie (91.1% good, AQI 35); Berrien (80.9% good, AQI 41); Cass (85.3% good, AQI 40); Clinton (90.2% good, AQI 39); Genesee (83.2% good, AQI 38).
Air Quality Summary
Good Days
71.8%
130 of 181 monitored days
-3.2pp vs 75% target
Max AQI Recorded
99
Moderate
Health Grade
Moderate
90th-pct AQI 58
Bay County, Good days share 71.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Bay County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 181 monitored days across EPA AQI categories.
Good
130
72%
Moderate
51
28%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Bay County.
- PM2.5 · 181 days · 100.0%
Health Impact Assessment
Moderate
Bay County's air quality is rated Moderate based on 71.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 71.8% of monitored days in 2025, with a median AQI of 38. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 181 of 181 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Bay County. Best year: 2020 (325 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 325 | 40 | 0 | 0 | 22 | 77 |
| 2021 | 290 | 73 | 0 | 0 | 28 | 86 |
| 2022 | 287 | 67 | 0 | 0 | 32 | 85 |
| 2023 | 229 | 128 | 3 | 3 | 42 | 192 |
| 2024 | 277 | 86 | 0 | 0 | 37 | 73 |
| 2025 | 130 | 51 | 0 | 0 | 38 | 99 |
How does Bay County compare?
How Bay County compares
Good-day share worse than US avg
Bay County 71.8%
Allegan County, Michigan 71.2%
US average 76.5%
Median AQI about average
Bay County 38
Allegan County, Michigan 43
US average 38
Unhealthy days / yr about average
Bay County 0
Allegan County, Michigan 1
US average 0
Other Counties in Michigan
Air quality comparison for nearby counties in Michigan.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Bay County.
Adams County, Illinois
AQI 38 · 94.4% good
Anoka County, Minnesota
AQI 38 · 82.1% good
Atlantic County, New Jersey
AQI 38 · 79.6% good
Avery County, North Carolina
AQI 38 · 93.9% good
Barnstable County, Massachusetts
AQI 38 · 92.5% good
Becker County, Minnesota
AQI 38 · 84.7% good
What Bay County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 38 means for exposure. Health guidance
- See how Bay County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Bay County with its Michigan neighbours before drawing a conclusion about the region. All of Michigan
Based on 181 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Bay County, Michigan? ▼
Bay County has a median Air Quality Index (AQI) of 38, rated "Good." 71.8% of monitored days (130 out of 181) had good air quality in 2025.
What is the main pollutant in Bay County? ▼
The primary pollutant in Bay County is Fine Particles (PM2.5), which was the main AQI driver on 181 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Bay County have? ▼
In 2025, Bay County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 99.
Is the air quality in Bay County getting better or worse? ▼
Air quality in Bay County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 325 good days. Worst year: 2025 with 130 good days.
What does AQI 38 mean for health? ▼
Bay County's median AQI of 38 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Bay County compare to other counties in Michigan? ▼
Bay County has 71.8% good air days. Nearby counties in Michigan: Allegan (71.2% good), Benzie (91.1% good), Berrien (80.9% good), Cass (85.3% good), Clinton (90.2% good), Genesee (83.2% good).
What is the 90th percentile AQI in Bay County? ▼
The 90th percentile AQI for Bay County is 58, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 99 (Moderate).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir 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.