Metro area air quality · 2025

Eureka-Arcata-Fortuna, CA

Median AQI 38 (Good). 78.1% of monitored days rated Good across this metro's EPA monitoring network.

38
Median AQI
78.1%
Good-air days
0
Unhealthy days
63%
Cleaner than US metros

Eureka-Arcata-Fortuna, CA posted a 2025 median AQI of 38 (Good) with 78.1% Good days

According to the U.S. EPA Air Quality System, the Eureka-Arcata-Fortuna, CA CBSA recorded a median AQI of 38 across 365 monitored days in 2025, with 78.1% rated Good and 0 unhealthy or worse. This is an annual metro comparison, not a live advisory.

Data source EPA Air Quality System (AQS)

Cleaner than US metros
The Eureka-Arcata-Fortuna, CA CBSA's 78.1% Good-day share places it cleaner than 63% of US metros in 2025.
Closest median-AQI peer
Appleton, WI (72.3% Good, median AQI 38) is the closest nationwide median-AQI peer to Eureka-Arcata-Fortuna, CA.
2020–2025 Good-day shift
Eureka-Arcata-Fortuna, CA's Good-day share moved -9.5 points from 2020 to 2025 (median AQI +9).
Median AQI
Median AQI: 38

Aggregated from EPA Air Quality System (2025), 365 monitored days. EPA AQS →

The verdict

Eureka-Arcata-Fortuna, CA's peak reading 87 stays in the lower max-AQI tercile on this extract. On the EPA scale the metro runs good, cleaner than the median US metro, with a median AQI of 38 and 78.1% of 365 monitored days in the Good band.

38
median AQI · Good
78.1%
days rated Good
63%
cleaner than US metros
87
worst single reading

No day crossed into the Unhealthy tier across the metro's monitors in 2025.

Annual release change

What changed in the 2025 EPA annual release

2024 → 2025
  • Eureka-Arcata-Fortuna, CA metro's Good-day share rose from 72.7% to 78.1% between the 2024 and 2025 EPA annual releases, a change of +5.4 percentage points.

Compared against 366 monitored days in 2024 and 365 in 2025. These are arithmetic differences between two stored EPA annual summaries, not a cause claim or a live advisory.

National release changes Two-year CSV

Eureka-Arcata-Fortuna, CA's peak reading 87 stays in the lower max-AQI tercile on this extract. Signature read: peak AQI 87 (low tercile vs CBSA corpus). Aggregated EPA AQS monitors across this Core-Based Statistical Area logged a median Air Quality Index of 38 over 365 measured days in 2025 (Good / Good). The monitored-day split lands at 285 Good (78%), 80 Moderate (22%), and 0 Unhealthy-for-Sensitive-Groups (0%). The 90th-percentile AQI finished at 55; the highest single-day reading hit 87 (Moderate).

Across 2020–2025, Good-day share shifted -9.5 points and median AQI moved +9 (worsening). No Unhealthy-tier days appear in this annual dataset. Metros with comparable AQI profiles include Appleton, WI (72.3% good, AQI 38); Billings, MT (86.3% good, AQI 38); Burlington-South Burlington, VT (87.7% good, AQI 38).

Understanding AQI →

Air Quality Summary

Median AQI

38

Good

Good Days

78.1%

285 of 365 days

Max AQI

87

Moderate

Health Grade

Good

90th pct: 55

AQI Day Breakdown (2025)

Distribution of 365 monitored days across EPA AQI categories.

Good

285

78%

Moderate

80

22%

USG

0

0%

Unhealthy

0

0%

Very Unhealthy

0

0%

Hazardous

0

0%

Health Impact Assessment

Good

The Eureka-Arcata-Fortuna, CA metro area's air quality is rated Good based on 78.1% good air days. No unhealthy air days were recorded in 2025.

Air quality is generally acceptable. Unusually sensitive people should monitor real-time conditions at AirNow.gov during high-pollution events.

How does the Eureka-Arcata-Fortuna, CA metro compare?

How Eureka-Arcata-Fortuna, CA compares

Good-day share better than typical
Eureka-Arcata-Fortuna, CA 78.1%
Appleton, WI 72.3%
Typical US metro 70.6%
Median AQI better than typical
Eureka-Arcata-Fortuna, CA 38
Appleton, WI 38
Typical US metro 41
Unhealthy days / yr better than typical
Eureka-Arcata-Fortuna, CA 0
Appleton, WI 6
Typical US metro 1

5-Year Air Quality Trend

Air quality is worsening in the Eureka-Arcata-Fortuna, CA metro. Highest Good-day share: 2022 (93.2%, 340 of 365 monitored days).

Year Good Moderate Unhealthy Median AQI
2020 318 44 1 29
2021 333 32 0 29
2022 340 25 0 24
2023 284 70 1 32
2024 266 100 0 38
2025 285 80 0 38

Metros with a similar median AQI

CBSA peers nationwide whose annual median AQI sits near Eureka-Arcata-Fortuna, CA (38).

Appleton, WI

Median AQI 38 · 72.3% Good-day share

38

Billings, MT

Median AQI 38 · 86.3% Good-day share

38

Burlington-South Burlington, VT

Median AQI 38 · 87.7% Good-day share

38

Charlottesville, VA

Median AQI 38 · 81.0% Good-day share

38

Corning, NY

Median AQI 38 · 83.3% Good-day share

38

Dickinson, ND

Median AQI 38 · 82.7% Good-day share

38

Metros with similar unhealthy-day exposure

A second relationship type: metros whose unhealthy-or-worse day count is closest to Eureka-Arcata-Fortuna, CA's 0 (independent of median AQI).

Aberdeen, SD

0 unhealthy-or-worse days · median AQI 27

27

Aberdeen, WA

0 unhealthy-or-worse days · median AQI 22

22

Adrian, MI

0 unhealthy-or-worse days · median AQI 41

41

Akron, OH

0 unhealthy-or-worse days · median AQI 45

45

Albany, GA

0 unhealthy-or-worse days · median AQI 46

46

Albany, OR

0 unhealthy-or-worse days · median AQI 27

27

Frequently Asked Questions

What is the 90th percentile AQI for Eureka-Arcata-Fortuna, CA? ▼
The 90th percentile AQI for the Eureka-Arcata-Fortuna, CA metro area is 55, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 87 (Moderate).
How many unhealthy air days does Eureka-Arcata-Fortuna, CA have? ▼
In 2025, the Eureka-Arcata-Fortuna, CA metro area recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 87.
What is the air quality in the Eureka-Arcata-Fortuna, CA metro area? ▼
The Eureka-Arcata-Fortuna, CA metro area has a median Air Quality Index (AQI) of 38, rated "Good." 78.1% of monitored days (285 out of 365) had good air quality in 2025.
Is air quality in Eureka-Arcata-Fortuna, CA getting better or worse? ▼
Air quality in the Eureka-Arcata-Fortuna, CA metro is worsening across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2022 at 93.2% (340 of 365 days). Lowest qualifying Good-day share: 2024 at 72.7% (266 of 366 days).
What does AQI 38 mean for health? ▼
An AQI of 38 is "Good", air quality is satisfactory and poses little or no health risk. This is the best category on the EPA's AQI scale.
How does Eureka-Arcata-Fortuna, CA compare to other metro areas? ▼
The Eureka-Arcata-Fortuna, CA metro has 78.1% good air days. Similar metros: Appleton, WI (72.3% good), Billings, MT (86.3% good), Burlington-South Burlington, VT (87.7% good).

Data Sources

Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by CBSA dataset for Eureka-Arcata-Fortuna, CA, 2025. See our methodology for how AQI, median, and coverage figures are computed.

Read our methodology , how this data is sourced, computed, and verified.

Source: U.S. EPA Air Quality System (AQS) Annual AQI by CBSA summary, Eureka-Arcata-Fortuna, CA · 2020–2025