Median AQI
44
Good
Colorado · County air quality · 2025
Grand County, Colorado
Median AQI 44 (Good). 79.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 79.8%
- Good-air days
- 0
- Unhealthy days
- 56%
- Cleaner than US counties
Grand County's 2025 annual median AQI is 44 (Good), with 79.8% Good days
According to the U.S. EPA Air Quality System, Grand County, Colorado posted a 2025 median AQI of 44 (Good) across 158 monitored days, with 79.8% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Grand County's 79.8% Good-day share places it cleaner than 56% of US counties in 2025.
- Closest median-AQI peer
- Allegan County (63.9% Good, median AQI 44) is the closest nationwide median-AQI peer to Grand County.
- 2020–2025 trend
- Grand County's floor-qualifying Good-day share is improving from 2020 to 2025 (76.6% → 79.7%).
- Median AQI
- Median AQI: 44
The verdict
According to EPA Air Quality System monitoring data, Grand County's air is good on balance, cleaner than the median US county, a median AQI of 44 with 79.8% of 158 monitored days in the Good band, driven mainly by Ozone.
- 44
- median AQI · Good
- 79.8%
- days rated Good
- Ozone
- main pollutant
- 56%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 77.
Annual release change
What changed in the 2025 EPA annual release
- Grand County's Good-day share fell from 82.6% to 79.7% between the 2024 and 2025 EPA annual releases, a change of -2.9 percentage points.
- Grand County's peak single-day AQI fell from 93 to 77 between the 2024 and 2025 EPA annual releases, a change of -16 points.
Data updated August 2026
- Good · 126 d · 79.7%
- Moderate · 32 d · 20.3%
How did Grand County's air break down in 2025?
Across 158 monitored days, 126 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 77 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 158 days monitored. Median AQI: 44 (Good).
Insights: Grand County, Colorado. EPA monitors recorded a median Air Quality Index of 44 across 158 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 126 (80%) fell in the Good band (AQI 0–50), 32 (20%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 61, while the worst single-day peak hit 77 (Moderate). Residents averaged about 23.9 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (158 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +3.2 points (measured against 175 monitored days in 2020 and 158 in 2025, so raw day counts are not comparable) and the median AQI moved -1 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 77, moderate but never Unhealthy. Nearby counties show comparable readings: Adams (55.1% good, AQI 49); Alamosa (91.5% good, AQI 25); Arapahoe (58.1% good, AQI 48); Archuleta (83.0% good, AQI 34); Boulder (58.4% good, AQI 48); Chaffee (66.0% good, AQI 48).
Air Quality Summary
Good Days
79.8%
126 of 158 monitored days
4.8pp vs 75% target
Max AQI Recorded
77
Moderate
Health Grade
Good
90th-pct AQI 61
Grand County, Good days share 79.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Grand 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 158 monitored days across EPA AQI categories.
Good
126
80%
Moderate
32
20%
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 Grand County.
- Ozone · 158 days · 100.0%
Health Impact Assessment
Good
Grand County's air quality is rated Good based on 79.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 79.8% of monitored days in 2025, with a median AQI of 44. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 158 of 158 monitored days.
5-Year Air Quality Trend
Air quality is improving in Grand County. Highest Good-day share: 2023 (82.9%, 131 of 158 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 134 | 39 | 2 | 0 | 45 | 112 |
| 2021 | 13 | 7 | 1 | 0 | 48 | 119 |
| 2022 | 136 | 38 | 0 | 0 | 44 | 80 |
| 2023 | 131 | 27 | 0 | 0 | 46 | 77 |
| 2024 | 133 | 28 | 0 | 0 | 45 | 93 |
| 2025 | 126 | 32 | 0 | 0 | 44 | 77 |
How does Grand County compare?
How Grand County compares
Good-day share better than US avg
Grand County 79.8%
Allegan County, Michigan 63.9%
US average 76.0%
Median AQI worse than US avg
Grand County 44
Allegan County, Michigan 44
US average 39
Unhealthy days / yr better than US avg
Grand County 0
Allegan County, Michigan 2
US average 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Grand County (44), not geographic neighbors.
Allegan County, Michigan
Median AQI 44 · 63.9% Good-day share
Allen County, Indiana
Median AQI 44 · 60.0% Good-day share
Baker County, Florida
Median AQI 44 · 69.5% Good-day share
Bay County, Florida
Median AQI 44 · 66.4% Good-day share
Blount County, Tennessee
Median AQI 44 · 71.5% Good-day share
Cache County, Utah
Median AQI 44 · 66.0% Good-day share
Same primary pollutant: Ozone
Ozone led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Dunn County, North Dakota
79.7% Good-day share · median AQI 39
Cecil County, Maryland
79.8% Good-day share · median AQI 41
Monongalia County, West Virginia
79.8% Good-day share · median AQI 42
Kiowa County, Oklahoma
79.7% Good-day share · median AQI 43
Nevada County, California
79.8% Good-day share · median AQI 42
Rock County, Wisconsin
79.9% Good-day share · median AQI 42
Colorado counties on the map
Geographic containment only, other monitored counties in Colorado, independent of AQI or pollutant match.
What Grand County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 44 means for exposure. Health guidance
- See how Grand County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Grand County with its Colorado neighbours before drawing a conclusion about the region. All of Colorado
Based on 158 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in Grand County, Colorado? ▼
Grand County has a median Air Quality Index (AQI) of 44, rated "Good." 79.8% of monitored days (126 out of 158) had good air quality in 2025.
What is the main pollutant in Grand County? ▼
The primary pollutant in Grand County is Ozone (O3), which was the main AQI driver on 158 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Grand County have? ▼
In 2025, Grand County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 77.
Is the air quality in Grand County getting better or worse? ▼
Air quality in Grand County is improving across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2023 at 82.9% (131 of 158 days). Lowest qualifying Good-day share: 2020 at 76.6% (134 of 175 days).
What does AQI 44 mean for health? ▼
Grand County's median AQI of 44 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Grand County compare to other counties in Colorado? ▼
Grand County has 79.8% good air days. Nearby counties in Colorado: Adams (55.1% good), Alamosa (91.5% good), Arapahoe (58.1% good), Archuleta (83.0% good), Boulder (58.4% good), Chaffee (66.0% good).
What is the 90th percentile AQI in Grand County? ▼
The 90th percentile AQI for Grand County is 61, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 77 (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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Grand County, Colorado · 2020–2025
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Every figure on PlainAirData 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.