Median AQI
42
Good
Idaho · County air quality · 2025
Ada County, Idaho
Median AQI 42 (Good). 74.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 42
- Median AQI
- 74.0%
- Good-air days
- 0
- Unhealthy days
- 42%
- Cleaner than US counties
Ada County's 2025 annual median AQI is 42 (Good), with 74.0% Good days
According to the U.S. EPA Air Quality System, Ada County, Idaho posted a 2025 median AQI of 42 (Good) across 365 monitored days, with 74.0% 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
- Ada County's 74.0% Good-day share places it cleaner than 42% of US counties in 2025.
- Closest median-AQI peer
- Adams County (74.4% Good, median AQI 42) is the closest nationwide median-AQI peer to Ada County.
- 2020–2025 trend
- Ada County's floor-qualifying Good-day share is improving from 2020 to 2025 (66.1% → 74.0%).
- Median AQI
- Median AQI: 42
The verdict
According to EPA Air Quality System monitoring data, Ada County's air is good on balance, more polluted than the median US county, a median AQI of 42 with 74.0% of 365 monitored days in the Good band, driven mainly by Ozone.
- 42
- median AQI · Good
- 74.0%
- days rated Good
- Ozone
- main pollutant
- 42%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 97.
Annual release change
What changed in the 2025 EPA annual release
- Ada County's peak single-day AQI fell from 214 to 97 between the 2024 and 2025 EPA annual releases, a change of -117 points.
- Ada County's Good-day share rose from 62.8% to 74.0% between the 2024 and 2025 EPA annual releases, a change of +11.1 percentage points.
- Ada County's Unhealthy-category days fell from 6 to 0 between the 2024 and 2025 EPA annual releases, a change of -6 days.
Data updated August 2026
- Good · 270 d · 74.0%
- Moderate · 95 d · 26.0%
How did Ada County's air break down in 2025?
Across 365 monitored days, 270 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 97 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 365 days monitored. Median AQI: 42 (Good).
Insights: Ada County, Idaho. EPA monitors recorded a median Air Quality Index of 42 across 365 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 270 (74%) fell in the Good band (AQI 0–50), 95 (26%) 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 97 (Moderate). Residents averaged about 22.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (209 days), PM2.5 (153 days), PM10 (3 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +7.9 points and the median AQI moved -2 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 97, moderate but never Unhealthy. Nearby counties show comparable readings: Bannock (88.8% good, AQI 36); Benewah (63.4% good, AQI 41); Blaine (96.6% good, AQI 17); Boise (70.4% good, AQI 42); Bonner (56.2% good, AQI 47); Bonneville (93.0% good, AQI 22).
Air Quality Summary
Good Days
74.0%
270 of 365 monitored days
-1.0pp vs 75% target
Max AQI Recorded
97
Moderate
Health Grade
Moderate
90th-pct AQI 61
Ada County, Good days share 74.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Ada 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 365 monitored days across EPA AQI categories.
Good
270
74%
Moderate
95
26%
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 Ada County.
- Ozone · 209 days · 57.3%
- PM2.5 · 153 days · 41.9%
- PM10 · 3 days · 0.8%
Health Impact Assessment
Moderate
Ada County's air quality is rated Moderate based on 74.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 74.0% of monitored days in 2025, with a median AQI of 42. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 209 of 365 monitored days.
5-Year Air Quality Trend
Air quality is improving in Ada County. Highest Good-day share: 2025 (74.0%, 270 of 365 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 242 | 106 | 11 | 7 | 44 | 198 |
| 2021 | 223 | 124 | 15 | 3 | 46 | 173 |
| 2022 | 196 | 162 | 6 | 1 | 48 | 166 |
| 2023 | 251 | 111 | 3 | 0 | 44 | 120 |
| 2024 | 230 | 101 | 28 | 6 | 44 | 214 |
| 2025 | 270 | 95 | 0 | 0 | 42 | 97 |
How does Ada County compare?
How Ada County compares
Good-day share worse than typical
Ada County 74.0%
Adams County, Pennsylvania 74.4%
Typical US county 76.0%
Median AQI worse than typical
Ada County 42
Adams County, Pennsylvania 42
Typical US county 39
Unhealthy days / yr better than typical
Ada County 0
Adams County, Pennsylvania 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Ada County (42), not geographic neighbors.
Adams County, Pennsylvania
Median AQI 42 · 74.4% Good-day share
Allen County, Ohio
Median AQI 42 · 67.0% Good-day share
Asotin County, Washington
Median AQI 42 · 61.9% Good-day share
Baldwin County, Alabama
Median AQI 42 · 75.5% Good-day share
Bell County, Kentucky
Median AQI 42 · 67.0% Good-day share
Belmont County, Ohio
Median AQI 42 · 63.0% 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).
Lackawanna County, Pennsylvania
74.0% Good-day share · median AQI 39
Love County, Oklahoma
74.1% Good-day share · median AQI 44
Anoka County, Minnesota
74.1% Good-day share · median AQI 38
Hunterdon County, New Jersey
74.2% Good-day share · median AQI 41
Rowan County, North Carolina
73.7% Good-day share · median AQI 43
Campbell County, Wyoming
74.3% Good-day share · median AQI 44
Idaho counties on the map
Geographic containment only, other monitored counties in Idaho, independent of AQI or pollutant match.
What Ada 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 42 means for exposure. Health guidance
- See how Ada County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Ada County with its Idaho neighbours before drawing a conclusion about the region. All of Idaho
Based on 365 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 Ada County, Idaho? ▼
Ada County has a median Air Quality Index (AQI) of 42, rated "Good." 74.0% of monitored days (270 out of 365) had good air quality in 2025.
What is the main pollutant in Ada County? ▼
The primary pollutant in Ada County is Ozone (O3), which was the main AQI driver on 209 days (57% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Ada County have? ▼
In 2025, Ada County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 97.
Is the air quality in Ada County getting better or worse? ▼
Air quality in Ada 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: 2025 at 74.0% (270 of 365 days). Lowest qualifying Good-day share: 2022 at 53.7% (196 of 365 days).
What does AQI 42 mean for health? ▼
Ada County's median AQI of 42 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Ada County compare to other counties in Idaho? ▼
Ada County has 74.0% good air days. Nearby counties in Idaho: Bannock (88.8% good), Benewah (63.4% good), Blaine (96.6% good), Boise (70.4% good), Bonner (56.2% good), Bonneville (93.0% good).
What is the 90th percentile AQI in Ada County? ▼
The 90th percentile AQI for Ada County is 61, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 97 (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 Ada County, Idaho · 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.