Metro area air quality · 2025
Boulder, CO
Median AQI 48 (Good). 58.4% of monitored days rated Good across this metro's EPA monitoring network.
- 48
- Median AQI
- 58.4%
- Good-air days
- 0
- Unhealthy days
- 23%
- Cleaner than US metros
Boulder, CO posted a 2025 median AQI of 48 (Good) with 58.4% Good days
According to the U.S. EPA Air Quality System, the Boulder, CO CBSA recorded a median AQI of 48 across 365 monitored days in 2025, with 58.4% 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 Boulder, CO CBSA's 58.4% Good-day share places it cleaner than 23% of US metros in 2025.
- Closest median-AQI peer
- Baltimore-Columbia-Towson, MD (58.1% Good, median AQI 48) is the closest nationwide median-AQI peer to Boulder, CO.
- 2020–2025 Good-day shift
- Boulder, CO's Good-day share moved +9.0 points from 2020 to 2025 (median AQI -3).
- Median AQI
- Median AQI: 48
Aggregated from EPA Air Quality System (2025), 365 monitored days. EPA AQS →
The verdict
Boulder, CO lands in the lower Good-day tercile (58.4% 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 48 and 58.4% of 365 monitored days in the Good band.
- 48
- median AQI · Good
- 58.4%
- days rated Good
- 23%
- cleaner than US metros
- 119
- 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
- Boulder, CO metro's peak single-day AQI fell from 154 to 119 between the 2024 and 2025 EPA annual releases, a change of -35 points.
- Boulder, CO metro's Unhealthy-category days fell from 1 to 0 between the 2024 and 2025 EPA annual releases, a change of -1 days.
Boulder, CO lands in the lower Good-day tercile (58.4% Good), a thinner clean-air share than most CBSA peers here. Signature read: 58.4% 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 48 over 365 measured days in 2025 (Good / Moderate). The monitored-day split lands at 213 Good (58%), 149 Moderate (41%), and 3 Unhealthy-for-Sensitive-Groups (1%). The 90th-percentile AQI finished at 71; the highest single-day reading hit 119 (USG).
Across 2020–2025, Good-day share shifted +9.0 points and median AQI moved -3 (improving). No Unhealthy-tier days appear in this annual dataset. Metros with comparable AQI profiles include Baltimore-Columbia-Towson, MD (58.1% good, AQI 48); Columbus, GA-AL (53.4% good, AQI 48); Durango, CO (60.8% good, AQI 48).
Air Quality Summary
Median AQI
48
Good
Good Days
58.4%
213 of 365 days
Max AQI
119
USG
Health Grade
Moderate
90th pct: 71
AQI Day Breakdown (2025)
Distribution of 365 monitored days across EPA AQI categories.
Good
213
58%
Moderate
149
41%
USG
3
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Health Impact Assessment
The Boulder, CO metro area's air quality is rated Moderate based on 58.4% 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 Boulder, CO metro compare?
How Boulder, CO compares
5-Year Air Quality Trend
Air quality is improving in the Boulder, CO metro. Highest Good-day share: 2022 (62.6%, 224 of 358 monitored days).
| Year | Good | Moderate | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|
| 2020 | 173 | 172 | 2 | 51 | 181 |
| 2021 | 154 | 176 | 3 | 52 | 160 |
| 2022 | 224 | 134 | 0 | 47 | 129 |
| 2023 | 192 | 167 | 2 | 50 | 181 |
| 2024 | 212 | 144 | 1 | 49 | 154 |
| 2025 | 213 | 149 | 0 | 48 | 119 |
Metros with a similar median AQI
CBSA peers nationwide whose annual median AQI sits near Boulder, CO (48).
Baltimore-Columbia-Towson, MD
Median AQI 48 · 58.1% Good-day share
Columbus, GA-AL
Median AQI 48 · 53.4% Good-day share
Durango, CO
Median AQI 48 · 60.8% Good-day share
Greenville-Anderson-Mauldin, SC
Median AQI 48 · 55.3% Good-day share
Knoxville, TN
Median AQI 48 · 56.4% Good-day share
Lake City, FL
Median AQI 48 · 57.3% Good-day share
Metros with similar unhealthy-day exposure
A second relationship type: metros whose unhealthy-or-worse day count is closest to Boulder, CO'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 Boulder, CO have? ▼
What is the air quality in the Boulder, CO metro area? ▼
Is air quality in Boulder, CO getting better or worse? ▼
What does AQI 48 mean for health? ▼
How does Boulder, CO compare to other metro areas? ▼
What is the 90th percentile AQI for Boulder, CO? ▼
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by CBSA dataset for Boulder, CO, 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, Boulder, CO · 2020–2025