Idaho · County air quality · 2025
Lemhi County, Idaho
Median AQI 29 (Good). 71.5% of monitored days rated Good, direct from EPA Air Quality System stations.
- 29
- Median AQI
- 71.5%
- Good-air days
- 1
- Unhealthy days
- 35%
- Cleaner than US counties
Lemhi County's 2025 annual median AQI is 29 (Good), with 71.5% Good days
According to the U.S. EPA Air Quality System, Lemhi County, Idaho posted a 2025 median AQI of 29 (Good) across 365 monitored days, with 71.5% rated Good and 1 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Lemhi County's 71.5% Good-day share places it cleaner than 35% of US counties in 2025.
- Closest median-AQI peer
- Baker County (83.3% Good, median AQI 29) is the closest nationwide median-AQI peer to Lemhi County.
- 2020–2025 trend
- Lemhi County's floor-qualifying Good-day share is improving from 2020 to 2025 (53.2% → 71.5%).
- Median AQI
- Median AQI: 29
According to the 2025 EPA AQS county release on PlainAirData, Lemhi County, Idaho ranks #89 of 951 by median AQI (29) and #611 by good-day share (71.5%). Ponce County, Puerto Rico is #1 of 951 by median AQI (3, 91.4% Good days) at good-day-share #159 ≠ largest of 7 at 100.0% Good days #1 by good-day share (100.0%, median AQI 9) at median-AQI #7.
Annual release change
What changed in the 2025 EPA annual release
- Lemhi County's Good-day share rose from 56.6% to 71.5% between the 2024 and 2025 EPA annual releases, a change of +14.9 percentage points.
- Lemhi County's peak single-day AQI fell from 198 to 163 between the 2024 and 2025 EPA annual releases, a change of -35 points.
- Lemhi County's Unhealthy-category days fell from 4 to 1 between the 2024 and 2025 EPA annual releases, a change of -3 days.
- Lemhi County's median AQI fell from 37 to 29 between the 2024 and 2025 EPA annual releases, a change of -8 points.
Data updated August 2026
- Good · 261 d · 71.5%
- Moderate · 102 d · 27.9%
- USG · 1 d · 0.3%
- Unhealthy · 1 d · 0.3%
How did Lemhi County's air break down in 2025?
Across 365 monitored days, 261 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 163 (Unhealthy).
EPA AQS →Share of monitored days at AQI 0-50 (Good band).
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
Where Lemhi County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Lemhi County's Good-day share is 71.5% - cleaner than 35% of that comparison set.
Lemhi County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
71.5% 35th percentile higher than 35% of 951 US counties
Each bar is a band; taller bars hold more US counties. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.
Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Lemhi County.
- PM2.5 · 365 days · 100.0%
2024 daily-monitor rhythm in Lemhi County
Month-by-month median AQI from EPA day-level county monitors (366 reported days in 2024). Jan posted the highest typical readings (median AQI 67, peak 111); May was cleanest at median 13. Summer months (Jun–Aug) averaged median AQI 44 vs 59 in Dec–Feb. 4 days crossed Unhealthy (AQI >150) at least once that year.
Five-year seasonal record
EPA day-level county files · 2020–20241,824 daily readings show a recurring local pattern: Jan has the highest matched-month median AQI (68), while May is lowest (19). Each cell is that month’s median daily AQI, not a current-air forecast.
Lower AQI is better. The colors summarize EPA AQI bands; gaps mean the county had no day-level record for that month.
Health Impact Assessment
Lemhi County's air quality is rated Moderate based on 71.5% good air days. There were 1 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 1 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 163. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 365 of 365 monitored days.
5-Year Air Quality Trend
Air quality is improving in Lemhi County. Highest Good-day share: 2025 (71.5%, 261 of 365 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 194 | 160 | 8 | 3 | 46 | 168 |
| 2021 | 188 | 157 | 16 | 4 | 47 | 172 |
| 2022 | 199 | 136 | 18 | 10 | 44 | 212 |
| 2023 | 251 | 110 | 2 | 0 | 32 | 119 |
| 2024 | 207 | 143 | 12 | 4 | 37 | 198 |
| 2025 | 261 | 102 | 1 | 1 | 29 | 163 |
How does Lemhi County compare?
How Lemhi County compares
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 Lemhi County, Idaho · 2020–2025
Download this county's annual AQI row as CSV , with the same EPA fields and denominator shown on this page.
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.