Median AQI
31
Good
California · County air quality · 2025
Lake County, California
Median AQI 31 (Good). 99.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 31
- Median AQI
- 99.2%
- Good-air days
- 0
- Unhealthy days
- 99%
- Cleaner than US counties
Lake County's 2025 annual median AQI is 31 (Good), with 99.2% Good days
According to the U.S. EPA Air Quality System, Lake County, California posted a 2025 median AQI of 31 (Good) across 363 monitored days, with 99.2% 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
- Lake County's 99.2% Good-day share places it cleaner than 99% of US counties in 2025.
- Closest median-AQI peer
- Athens County (83.4% Good, median AQI 31) is the closest nationwide median-AQI peer to Lake County.
- 2020–2025 trend
- Lake County's floor-qualifying Good-day share is stable from 2020 to 2025 (97.2% → 99.2%).
- Median AQI
- Median AQI: 31
The verdict
According to EPA Air Quality System monitoring data, Lake County's air is good on balance, among the cleanest 1% of US counties, a median AQI of 31 with 99.2% of 363 monitored days in the Good band, driven mainly by Ozone.
- 31
- median AQI · Good
- 99.2%
- days rated Good
- Ozone
- main pollutant
- 99%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 74.
Data updated August 2026
- Good · 360 d · 99.2%
- Moderate · 3 d · 0.8%
How did Lake County's air break down in 2025?
Across 363 monitored days, 360 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 74 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 363 days monitored. Median AQI: 31 (Good).
Insights: Lake County, California. EPA monitors recorded a median Air Quality Index of 31 across 363 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 360 (99%) fell in the Good band (AQI 0–50), 3 (1%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 39, while the worst single-day peak hit 74 (Moderate). Residents averaged about 29.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (352 days), PM2.5 (11 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +2.0 points and the median AQI moved -1 points, placing the multi-year trajectory at stable. The worst single reading over the 2020–2025 window was AQI 74, moderate but never Unhealthy. Nearby counties show comparable readings: Alameda (53.0% good, AQI 49); Amador (87.4% good, AQI 38); Butte (65.2% good, AQI 46); Calaveras (82.2% good, AQI 40); Colusa (79.2% good, AQI 40); Contra Costa (53.5% good, AQI 48).
Air Quality Summary
Good Days
99.2%
360 of 363 monitored days
24.2pp vs 75% target
Max AQI Recorded
74
Moderate
Health Grade
Excellent
90th-pct AQI 39
Lake County, Good days share 99.2%
National avg
Share of monitored days at AQI 0-50 (Good band).
Lake 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 363 monitored days across EPA AQI categories.
Good
360
99%
Moderate
3
1%
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 Lake County.
- Ozone · 352 days · 97.0%
- PM2.5 · 11 days · 3.0%
Health Impact Assessment
Excellent
Lake County's air quality is rated Excellent based on 99.2% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 99.2% of monitored days in 2025, with a median AQI of 31. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 352 of 363 monitored days.
5-Year Air Quality Trend
Air quality is stable in Lake County. Highest Good-day share: 2024 (99.4%, 361 of 363 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 341 | 6 | 1 | 3 | 32 | 190 |
| 2021 | 348 | 7 | 0 | 1 | 33 | 157 |
| 2022 | 359 | 4 | 0 | 0 | 32 | 76 |
| 2023 | 357 | 6 | 0 | 0 | 32 | 67 |
| 2024 | 361 | 2 | 0 | 0 | 32 | 67 |
| 2025 | 360 | 3 | 0 | 0 | 31 | 74 |
How does Lake County compare?
How Lake County compares
Good-day share better than typical
Lake County 99.2%
Athens County, Ohio 83.4%
Typical US county 76.0%
Median AQI better than typical
Lake County 31
Athens County, Ohio 31
Typical US county 39
Unhealthy days / yr better than typical
Lake County 0
Athens County, Ohio 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Lake County (31), not geographic neighbors.
Athens County, Ohio
Median AQI 31 · 83.4% Good-day share
Clackamas County, Oregon
Median AQI 31 · 87.6% Good-day share
Grant County, Oklahoma
Median AQI 31 · 82.3% Good-day share
Kent County, Rhode Island
Median AQI 31 · 92.8% Good-day share
Kootenai County, Idaho
Median AQI 31 · 77.8% Good-day share
Lake County, Minnesota
Median AQI 31 · 85.9% 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).
Solano County, California
99.2% Good-day share · median AQI 33
Denali County, Alaska
99.7% Good-day share · median AQI 33
Liberty County, Florida
98.5% Good-day share · median AQI 33
Carbon County, Wyoming
100.0% Good-day share · median AQI 8
Martin County, North Carolina
100.0% Good-day share · median AQI 31
Flagler County, Florida
98.1% Good-day share · median AQI 34
California counties on the map
Geographic containment only, other monitored counties in California, independent of AQI or pollutant match.
What Lake 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 31 means for exposure. Health guidance
- See how Lake County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Lake County with its California neighbours before drawing a conclusion about the region. All of California
Based on 363 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 Lake County, California? ▼
Lake County has a median Air Quality Index (AQI) of 31, rated "Good." 99.2% of monitored days (360 out of 363) had good air quality in 2025.
What is the main pollutant in Lake County? ▼
The primary pollutant in Lake County is Ozone (O3), which was the main AQI driver on 352 days (97% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Lake County have? ▼
In 2025, Lake County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 74.
Is the air quality in Lake County getting better or worse? ▼
Air quality in Lake County is stable across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2024 at 99.4% (361 of 363 days). Lowest qualifying Good-day share: 2020 at 97.2% (341 of 351 days).
What does AQI 31 mean for health? ▼
Lake County's median AQI of 31 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Lake County compare to other counties in California? ▼
Lake County has 99.2% good air days. Nearby counties in California: Alameda (53.0% good), Amador (87.4% good), Butte (65.2% good), Calaveras (82.2% good), Colusa (79.2% good), Contra Costa (53.5% good).
What is the 90th percentile AQI in Lake County? ▼
The 90th percentile AQI for Lake County is 39, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 74 (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 Lake County, California · 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.