Median AQI
33
Good
California · County air quality · 2025
Del Norte County, California
Median AQI 33 (Good). 81.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 33
- Median AQI
- 81.0%
- Good-air days
- 0
- Unhealthy days
- 55%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Del Norte County's air is good on balance, cleaner than the median US county, a median AQI of 33 with 81.0% of 179 monitored days in the Good band, driven mainly by PM2.5.
- 33
- median AQI · Good
- 81.0%
- days rated Good
- PM2.5
- main pollutant
- 55%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 70.
Data updated July 2026
- Good · 145 d · 81.0%
- Moderate · 34 d · 19.0%
How did Del Norte County's air break down in 2025?
Across 179 monitored days, 145 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 70 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 179 days monitored. Median AQI: 33 (Good).
Insights: Del Norte County, California. EPA monitors recorded a median Air Quality Index of 33 across 179 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 145 (81%) fell in the Good band (AQI 0–50), 34 (19%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 54, while the worst single-day peak hit 70 (Moderate). Residents averaged about 24.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (179 days). Across the 2020–2025 trend window, good days shifted by -48 and the median AQI moved -9 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 70, moderate but never Unhealthy. Nearby counties show comparable readings: Amador (84.8% good, AQI 40); Butte (66.1% good, AQI 47); Calaveras (73.9% good, AQI 43); Colusa (84.9% good, AQI 39); El Dorado (85.8% good, AQI 39); Fresno (40.1% good, AQI 54).
Air Quality Summary
Good Days
81.0%
145 of 179 monitored days
6.0pp vs 75% target
Max AQI Recorded
70
Moderate
Health Grade
Good
90th-pct AQI 54
Del Norte County, Good days share 81.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Del Norte 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 179 monitored days across EPA AQI categories.
Good
145
81%
Moderate
34
19%
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 Del Norte County.
- PM2.5 · 179 days · 100.0%
Health Impact Assessment
Good
Del Norte County's air quality is rated Good based on 81.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 81.0% of monitored days in 2025, with a median AQI of 33. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 179 of 179 monitored days.
5-Year Air Quality Trend
Air quality is improving in Del Norte County. Best year: 2022 (299 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 193 | 90 | 4 | 3 | 42 | 245 |
| 2021 | 259 | 64 | 0 | 0 | 31 | 72 |
| 2022 | 299 | 45 | 0 | 0 | 29 | 74 |
| 2023 | 268 | 52 | 6 | 2 | 32 | 187 |
| 2024 | 232 | 55 | 2 | 0 | 32 | 125 |
| 2025 | 145 | 34 | 0 | 0 | 33 | 70 |
How does Del Norte County compare?
How Del Norte County compares
Good-day share better than US avg
Del Norte County 81.0%
Amador County, California 84.8%
US average 76.5%
Median AQI better than US avg
Del Norte County 33
Amador County, California 40
US average 38
Unhealthy days / yr about average
Del Norte County 0
Amador County, California 0
US average 0
Other Counties in California
Air quality comparison for nearby counties in California.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Del Norte County.
Ascension County, Louisiana
AQI 33 · 94.1% good
Athens County, Ohio
AQI 33 · 80.3% good
Brazoria County, Texas
AQI 33 · 84.8% good
Bristol City County, Virginia
AQI 33 · 78.3% good
Carter County, Oklahoma
AQI 33 · 80.9% good
Codington County, South Dakota
AQI 33 · 82.1% good
What Del Norte 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 33 means for exposure. Health guidance
- See how Del Norte County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Del Norte County with its California neighbours before drawing a conclusion about the region. All of California
Based on 179 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 Del Norte County, California? ▼
Del Norte County has a median Air Quality Index (AQI) of 33, rated "Good." 81.0% of monitored days (145 out of 179) had good air quality in 2025.
What is the main pollutant in Del Norte County? ▼
The primary pollutant in Del Norte County is Fine Particles (PM2.5), which was the main AQI driver on 179 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Del Norte County have? ▼
In 2025, Del Norte County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 70.
Is the air quality in Del Norte County getting better or worse? ▼
Air quality in Del Norte County is improving based on 5-year trends (2020-2025). Best year: 2022 with 299 good days. Worst year: 2025 with 145 good days.
What does AQI 33 mean for health? ▼
Del Norte County's median AQI of 33 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 Del Norte County compare to other counties in California? ▼
Del Norte County has 81.0% good air days. Nearby counties in California: Amador (84.8% good), Butte (66.1% good), Calaveras (73.9% good), Colusa (84.9% good), El Dorado (85.8% good), Fresno (40.1% good).
What is the 90th percentile AQI in Del Norte County? ▼
The 90th percentile AQI for Del Norte County is 54, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 70 (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.