Median AQI
37
Good
California · County air quality · 2025
Santa Cruz County, California
Median AQI 37 (Good). 81.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 37
- Median AQI
- 81.8%
- Good-air days
- 0
- Unhealthy days
- 57%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Santa Cruz County's air is good on balance, cleaner than the median US county, a median AQI of 37 with 81.8% of 181 monitored days in the Good band, driven mainly by Ozone.
- 37
- median AQI · Good
- 81.8%
- days rated Good
- Ozone
- main pollutant
- 57%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 71.
Data updated July 2026
- Good · 148 d · 81.8%
- Moderate · 33 d · 18.2%
How did Santa Cruz County's air break down in 2025?
Across 181 monitored days, 148 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 71 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 37 (Good).
Insights: Santa Cruz County, California. EPA monitors recorded a median Air Quality Index of 37 across 181 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 148 (82%) fell in the Good band (AQI 0–50), 33 (18%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 57, while the worst single-day peak hit 71 (Moderate). Residents averaged about 24.5 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (98 days), PM2.5 (83 days). Across the 2020–2025 trend window, good days shifted by -113 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 71, 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); Del Norte (81.0% good, AQI 33); El Dorado (85.8% good, AQI 39).
Air Quality Summary
Good Days
81.8%
148 of 181 monitored days
6.8pp vs 75% target
Max AQI Recorded
71
Moderate
Health Grade
Good
90th-pct AQI 57
Santa Cruz County, Good days share 81.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Santa Cruz 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 181 monitored days across EPA AQI categories.
Good
148
82%
Moderate
33
18%
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 Santa Cruz County.
- Ozone · 98 days · 54.1%
- PM2.5 · 83 days · 45.9%
Health Impact Assessment
Good
Santa Cruz County's air quality is rated Good based on 81.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 81.8% of monitored days in 2025, with a median AQI of 37. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 98 of 181 monitored days.
5-Year Air Quality Trend
Air quality is improving in Santa Cruz County. Best year: 2023 (300 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 261 | 85 | 6 | 10 | 39 | 624 |
| 2021 | 298 | 67 | 0 | 0 | 37 | 80 |
| 2022 | 287 | 78 | 0 | 0 | 35 | 93 |
| 2023 | 300 | 64 | 1 | 0 | 36 | 130 |
| 2024 | 293 | 73 | 0 | 0 | 39 | 80 |
| 2025 | 148 | 33 | 0 | 0 | 37 | 71 |
How does Santa Cruz County compare?
How Santa Cruz County compares
Good-day share better than US avg
Santa Cruz County 81.8%
Amador County, California 84.8%
US average 76.5%
Median AQI better than US avg
Santa Cruz County 37
Amador County, California 40
US average 38
Unhealthy days / yr about average
Santa Cruz 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 Santa Cruz County.
Alachua County, Florida
AQI 37 · 90.1% good
Beltrami County, Minnesota
AQI 37 · 88.8% good
Benewah County, Idaho
AQI 37 · 74.6% good
Brevard County, Florida
AQI 37 · 89.7% good
Brown County, Indiana
AQI 37 · 94.5% good
Brown County, Wisconsin
AQI 37 · 79.0% good
What Santa Cruz 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 37 means for exposure. Health guidance
- See how Santa Cruz County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Santa Cruz County with its California neighbours before drawing a conclusion about the region. All of California
Based on 181 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 Santa Cruz County, California? ▼
Santa Cruz County has a median Air Quality Index (AQI) of 37, rated "Good." 81.8% of monitored days (148 out of 181) had good air quality in 2025.
What is the main pollutant in Santa Cruz County? ▼
The primary pollutant in Santa Cruz County is Ozone (O3), which was the main AQI driver on 98 days (54% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Santa Cruz County have? ▼
In 2025, Santa Cruz County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 71.
Is the air quality in Santa Cruz County getting better or worse? ▼
Air quality in Santa Cruz County is improving based on 5-year trends (2020-2025). Best year: 2023 with 300 good days. Worst year: 2025 with 148 good days.
What does AQI 37 mean for health? ▼
Santa Cruz County's median AQI of 37 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 Santa Cruz County compare to other counties in California? ▼
Santa Cruz County has 81.8% good air days. Nearby counties in California: Amador (84.8% good), Butte (66.1% good), Calaveras (73.9% good), Colusa (84.9% good), Del Norte (81.0% good), El Dorado (85.8% good).
What is the 90th percentile AQI in Santa Cruz County? ▼
The 90th percentile AQI for Santa Cruz County is 57, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 71 (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.