Median AQI
24
Good
Colorado · County air quality · 2025
Alamosa County, Colorado
Median AQI 24 (Good). 90.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 24
- Median AQI
- 90.8%
- Good-air days
- 0
- Unhealthy days
- 78%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Alamosa County's air is good on balance, cleaner than most US counties, a median AQI of 24 with 90.8% of 273 monitored days in the Good band, driven mainly by PM2.5.
- 24
- median AQI · Good
- 90.8%
- days rated Good
- PM2.5
- main pollutant
- 78%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 76.
Data updated July 2026
- Good · 248 d · 90.8%
- Moderate · 25 d · 9.2%
How did Alamosa County's air break down in 2025?
Across 273 monitored days, 248 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 76 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 273 days monitored. Median AQI: 24 (Good).
Insights: Alamosa County, Colorado. EPA monitors recorded a median Air Quality Index of 24 across 273 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 248 (91%) fell in the Good band (AQI 0–50), 25 (9%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 49, while the worst single-day peak hit 76 (Moderate). Residents averaged about 27.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (230 days), PM10 (43 days). Across the 2020–2025 trend window, good days shifted by +136 and the median AQI moved +10 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 76, moderate but never Unhealthy. Nearby counties show comparable readings: Adams (50.2% good, AQI 50); Arapahoe (47.3% good, AQI 51); Archuleta (79.5% good, AQI 32); Boulder (50.9% good, AQI 50); Clear Creek (64.4% good, AQI 48); Delta (88.0% good, AQI 28).
Air Quality Summary
Good Days
90.8%
248 of 273 monitored days
15.8pp vs 75% target
Max AQI Recorded
76
Moderate
Health Grade
Excellent
90th-pct AQI 49
Alamosa County, Good days share 90.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Alamosa 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 273 monitored days across EPA AQI categories.
Good
248
91%
Moderate
25
9%
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 Alamosa County.
- PM2.5 · 230 days · 84.2%
- PM10 · 43 days · 15.8%
Health Impact Assessment
Excellent
Alamosa County's air quality is rated Excellent based on 90.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 90.8% of monitored days in 2025, with a median AQI of 24. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 230 of 273 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Alamosa County. Best year: 2024 (325 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 112 | 7 | 0 | 0 | 14 | 65 |
| 2021 | 114 | 5 | 1 | 0 | 12 | 109 |
| 2022 | 107 | 8 | 1 | 0 | 11 | 134 |
| 2023 | 142 | 23 | 0 | 0 | 22 | 70 |
| 2024 | 325 | 40 | 0 | 0 | 26 | 98 |
| 2025 | 248 | 25 | 0 | 0 | 24 | 76 |
How does Alamosa County compare?
How Alamosa County compares
Good-day share better than US avg
Alamosa County 90.8%
Adams County, Colorado 50.2%
US average 76.5%
Median AQI better than US avg
Alamosa County 24
Adams County, Colorado 50
US average 38
Unhealthy days / yr about average
Alamosa County 0
Adams County, Colorado 0
US average 0
Other Counties in Colorado
Air quality comparison for nearby counties in Colorado.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Alamosa County.
Anchorage County, Alaska
AQI 24 · 80.8% good
Charlton County, Georgia
AQI 24 · 79.0% good
Crook County, Oregon
AQI 24 · 80.7% good
Culberson County, Texas
AQI 24 · 80.0% good
Kootenai County, Idaho
AQI 24 · 88.4% good
Lake County, Oregon
AQI 24 · 82.8% good
What Alamosa 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 24 means for exposure. Health guidance
- See how Alamosa County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Alamosa County with its Colorado neighbours before drawing a conclusion about the region. All of Colorado
Based on 273 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 Alamosa County, Colorado? ▼
Alamosa County has a median Air Quality Index (AQI) of 24, rated "Good." 90.8% of monitored days (248 out of 273) had good air quality in 2025.
What is the main pollutant in Alamosa County? ▼
The primary pollutant in Alamosa County is Fine Particles (PM2.5), which was the main AQI driver on 230 days (84% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Alamosa County have? ▼
In 2025, Alamosa County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 76.
Is the air quality in Alamosa County getting better or worse? ▼
Air quality in Alamosa County is worsening based on 5-year trends (2020-2025). Best year: 2024 with 325 good days. Worst year: 2022 with 107 good days.
What does AQI 24 mean for health? ▼
Alamosa County's median AQI of 24 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 Alamosa County compare to other counties in Colorado? ▼
Alamosa County has 90.8% good air days. Nearby counties in Colorado: Adams (50.2% good), Arapahoe (47.3% good), Archuleta (79.5% good), Boulder (50.9% good), Clear Creek (64.4% good), Delta (88.0% good).
What is the 90th percentile AQI in Alamosa County? ▼
The 90th percentile AQI for Alamosa County is 49, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 76 (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.