Metro area air quality · 2025
Modesto, CA
Median AQI 51 (Moderate). 49.9% of monitored days rated Good across this metro's EPA monitoring network.
- 51
- Median AQI
- 49.9%
- Good-air days
- 0
- Unhealthy days
- 12%
- Cleaner than US metros
Modesto, CA posted a 2025 median AQI of 51 (Moderate) with 49.9% Good days
According to the U.S. EPA Air Quality System, the Modesto, CA CBSA recorded a median AQI of 51 across 365 monitored days in 2025, with 49.9% 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 Modesto, CA CBSA's 49.9% Good-day share places it cleaner than 12% of US metros in 2025.
- Closest median-AQI peer
- Boise City, ID (49.9% Good, median AQI 51) is the closest nationwide median-AQI peer to Modesto, CA.
- 2020–2025 Good-day shift
- Modesto, CA's Good-day share moved +12.3 points from 2020 to 2025 (median AQI -9).
- Median AQI
- Median AQI: 51
Aggregated from EPA Air Quality System (2025), 365 monitored days. EPA AQS →
The verdict
Modesto, CA lands in the lower Good-day tercile (49.9% Good), a thinner clean-air share than most CBSA peers here. On the EPA scale the metro runs moderate, among the more polluted US metros, with a median AQI of 51 and 49.9% of 365 monitored days in the Good band.
- 51
- median AQI · Moderate
- 49.9%
- days rated Good
- 12%
- cleaner than US metros
- 115
- 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
- Modesto, CA metro's peak single-day AQI fell from 150 to 115 between the 2024 and 2025 EPA annual releases, a change of -35 points.
Modesto, CA lands in the lower Good-day tercile (49.9% Good), a thinner clean-air share than most CBSA peers here. Signature read: 49.9% 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 51 over 365 measured days in 2025 (Moderate / Poor). The monitored-day split lands at 182 Good (50%), 180 Moderate (49%), and 3 Unhealthy-for-Sensitive-Groups (1%). The 90th-percentile AQI finished at 80; the highest single-day reading hit 115 (USG).
Across 2020–2025, Good-day share shifted +12.3 points and median AQI moved -9 (improving). No Unhealthy-tier days appear in this annual dataset. Metros with comparable AQI profiles include Boise City, ID (49.9% good, AQI 51); Hot Springs, AR (49.2% good, AQI 51); Kansas City, MO-KS (49.3% good, AQI 51).
Air Quality Summary
Median AQI
51
Moderate
Good Days
49.9%
182 of 365 days
Max AQI
115
USG
Health Grade
Poor
90th pct: 80
AQI Day Breakdown (2025)
Distribution of 365 monitored days across EPA AQI categories.
Good
182
50%
Moderate
180
49%
USG
3
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Health Impact Assessment
The Modesto, CA metro area's air quality is rated Poor based on 49.9% 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 Modesto, CA metro compare?
How Modesto, CA compares
5-Year Air Quality Trend
Air quality is improving in the Modesto, CA metro. Highest Good-day share: 2024 (50.6%, 166 of 328 monitored days).
| Year | Good | Moderate | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|
| 2020 | 131 | 198 | 16 | 60 | 195 |
| 2021 | 84 | 234 | 5 | 61 | 172 |
| 2022 | 108 | 234 | 1 | 57 | 166 |
| 2023 | 166 | 176 | 0 | 54 | 150 |
| 2024 | 166 | 162 | 0 | 53 | 150 |
| 2025 | 182 | 180 | 0 | 51 | 115 |
Metros with a similar median AQI
CBSA peers nationwide whose annual median AQI sits near Modesto, CA (51).
Boise City, ID
Median AQI 51 · 49.9% Good-day share
Hot Springs, AR
Median AQI 51 · 49.2% Good-day share
Kansas City, MO-KS
Median AQI 51 · 49.3% Good-day share
Laredo, TX
Median AQI 51 · 49.9% Good-day share
Tulsa, OK
Median AQI 51 · 49.6% Good-day share
Waco, TX
Median AQI 51 · 46.6% Good-day share
Metros with similar unhealthy-day exposure
A second relationship type: metros whose unhealthy-or-worse day count is closest to Modesto, 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 Modesto, CA have? ▼
What is the air quality in the Modesto, CA metro area? ▼
Is air quality in Modesto, CA getting better or worse? ▼
What does AQI 51 mean for health? ▼
How does Modesto, CA compare to other metro areas? ▼
What is the 90th percentile AQI for Modesto, CA? ▼
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by CBSA dataset for Modesto, 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, Modesto, CA · 2020–2025