Metro area air quality · 2025
Merced, CA
Median AQI 50 (Good). 51.0% of monitored days rated Good across this metro's EPA monitoring network.
- 50
- Median AQI
- 51.0%
- Good-air days
- 0
- Unhealthy days
- 13%
- Cleaner than US metros
Merced, CA posted a 2025 median AQI of 50 (Good) with 51.0% Good days
According to the U.S. EPA Air Quality System, the Merced, CA CBSA recorded a median AQI of 50 across 365 monitored days in 2025, with 51.0% 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 Merced, CA CBSA's 51.0% Good-day share places it cleaner than 13% of US metros in 2025.
- Closest median-AQI peer
- Fort Collins, CO (50.7% Good, median AQI 50) is the closest nationwide median-AQI peer to Merced, CA.
- 2020–2025 Good-day shift
- Merced, CA's Good-day share moved +13.4 points from 2020 to 2025 (median AQI -7).
- Median AQI
- Median AQI: 50
Aggregated from EPA Air Quality System (2025), 365 monitored days. EPA AQS →
The verdict
Merced, CA lands in the lower Good-day tercile (51.0% Good), a thinner clean-air share than most CBSA peers here. On the EPA scale the metro runs good, among the more polluted US metros, with a median AQI of 50 and 51.0% of 365 monitored days in the Good band.
- 50
- median AQI · Good
- 51.0%
- days rated Good
- 13%
- cleaner than US metros
- 100
- 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
- Merced, CA metro's peak single-day AQI fell from 151 to 100 between the 2024 and 2025 EPA annual releases, a change of -51 points.
- Merced, CA metro's Unhealthy-category days fell from 1 to 0 between the 2024 and 2025 EPA annual releases, a change of -1 days.
Merced, CA lands in the lower Good-day tercile (51.0% Good), a thinner clean-air share than most CBSA peers here. Signature read: 51.0% Good-day share (low tercile vs CBSA corpus). Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 50 over 365 measured days in 2025 (Good / Moderate). The monitored-day split lands at 186 Good (51%), 179 Moderate (49%), and 0 Unhealthy-for-Sensitive-Groups (0%). The 90th-percentile AQI finished at 77; the highest single-day reading hit 100 (Moderate).
Across 2020–2025, Good-day share shifted +13.4 points and median AQI moved -7 (improving). No Unhealthy-tier days appear in this annual dataset. Metros with comparable AQI profiles include Fort Collins, CO (50.7% good, AQI 50); Madera, CA (50.4% good, AQI 50); Nashville-Davidson--Murfreesboro--Franklin, TN (51.2% good, AQI 50).
Air Quality Summary
Median AQI
50
Good
Good Days
51.0%
186 of 365 days
Max AQI
100
Moderate
Health Grade
Moderate
90th pct: 77
AQI Day Breakdown (2025)
Distribution of 365 monitored days across EPA AQI categories.
Good
186
51%
Moderate
179
49%
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 51.0% 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. Highest Good-day share: 2025 (51.0%, 186 of 365 monitored 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 | 186 | 179 | 0 | 50 | 100 |
Metros with a similar median AQI
CBSA peers nationwide whose annual median AQI sits near Merced, CA (50).
Fort Collins, CO
Median AQI 50 · 50.7% Good-day share
Madera, CA
Median AQI 50 · 50.4% Good-day share
Nashville-Davidson--Murfreesboro--Franklin, TN
Median AQI 50 · 51.2% Good-day share
Oxnard-Thousand Oaks-Ventura, CA
Median AQI 50 · 52.0% Good-day share
Reno, NV
Median AQI 50 · 50.1% Good-day share
San Luis Obispo-Paso Robles-Arroyo Grande, CA
Median AQI 50 · 52.3% Good-day share
Metros with similar unhealthy-day exposure
A second relationship type: metros whose unhealthy-or-worse day count is closest to Merced, CA'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
How many unhealthy air days does Merced, CA have? ▼
What is the air quality in the Merced, CA metro area? ▼
Is air quality in Merced, CA getting better or worse? ▼
What does AQI 50 mean for health? ▼
How does Merced, CA compare to other metro areas? ▼
What is the 90th percentile AQI for Merced, CA? ▼
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by CBSA dataset for Merced, CA, 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, Merced, CA · 2020–2025