Metro area air quality · 2025
Merced, CA
Median AQI 43 (Good). 64.4% of monitored days rated Good across this metro's EPA monitoring network.
- 43
- Median AQI
- 64.4%
- Good-air days
- 0
- Unhealthy days
- 33%
- Cleaner than US metros
Aggregated from EPA Air Quality System (2025), 90 monitored days. EPA AQS →
The verdict
The Merced, CA metro runs good on the EPA scale, more polluted than the median US metro, a median AQI of 43 with 64.4% of 90 monitored days in the Good band.
- 43
- median AQI · Good
- 64.4%
- days rated Good
- 33%
- cleaner than US metros
- 78
- worst single reading
No day crossed into the Unhealthy tier across the metro's monitors in 2025.
Insights: Merced, CA metro. Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 43 over 90 measured days in 2025, which corresponds to a Good band and a Moderate metro-wide health grade. The monitored-day split lands at 58 Good days (64%), 32 Moderate (36%), and 0 Unhealthy-for-Sensitive-Groups (0%). The 90th-percentile AQI finished at 68 while the highest single-day reading hit 78 (Moderate). Metro residents averaged roughly 19.3 clean-air days per 30-day window across the reporting year.
Across the 2020–2025 trend window, good days shifted by -73 and the median AQI moved -14 points, which classifies the multi-year trajectory as improving. The metro avoided any Unhealthy-tier days entirely, an outcome that typically reflects favorable wind patterns, lower industrial density, or effective regional emission controls. Metros with comparable AQI profiles include Allentown-Bethlehem-Easton, PA-NJ (65.6% good, AQI 43); Amarillo, TX (75.7% good, AQI 43); Ashtabula, OH (81.2% good, AQI 43).
Air Quality Summary
Median AQI
43
Good
Good Days
64.4%
58 of 90 days
Max AQI
78
Moderate
Health Grade
Moderate
90th pct: 68
AQI Day Breakdown (2025)
Distribution of 90 monitored days across EPA AQI categories.
Good
58
64%
Moderate
32
36%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Health Impact Assessment
The Merced, CA metro area's air quality is rated Moderate based on 64.4% 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 Merced, CA metro compare?
How Merced, CA compares
5-Year Air Quality Trend
Air quality is improving in the Merced, CA metro. Best year: 2023 (171 good days).
| Year | Good | Moderate | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|
| 2020 | 131 | 203 | 15 | 57 | 194 |
| 2021 | 155 | 177 | 2 | 54 | 166 |
| 2022 | 140 | 212 | 0 | 56 | 143 |
| 2023 | 171 | 179 | 0 | 51 | 129 |
| 2024 | 168 | 163 | 1 | 52 | 151 |
| 2025 | 58 | 32 | 0 | 43 | 78 |
Metros with Similar Air Quality
Metro areas across the US with a similar median AQI to Merced, CA.
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Worst Air Quality
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All Metro Areas
Annual AQI by CBSA for every monitored U.S. metro area.
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Air Quality Guides
Frequently Asked Questions
What is the air quality in the Merced, CA metro area? ▼
How many unhealthy air days does Merced, CA have? ▼
Is air quality in Merced, CA getting better or worse? ▼
What does AQI 43 mean for health? ▼
What is the 90th percentile AQI for Merced, CA? ▼
How does Merced, CA 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
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.