Median AQI
64
Moderate
California · County air quality · 2025
Imperial County, California
Median AQI 64 (Moderate). 27.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 64
- Median AQI
- 27.4%
- Good-air days
- 6
- Unhealthy days
- 1%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Imperial County's air is moderate on balance, among the most polluted counties nationally, a median AQI of 64 with 27.4% of 219 monitored days in the Good band, driven mainly by Ozone.
- 64
- median AQI · Moderate
- 27.4%
- days rated Good
- Ozone
- main pollutant
- 1%
- cleaner than US counties
6 days reached Unhealthy or worse; the worst single reading hit AQI 190.
Data updated July 2026
- Good · 60 d · 27.4%
- Moderate · 132 d · 60.3%
- USG · 21 d · 9.6%
- Unhealthy · 6 d · 2.7%
How did Imperial County's air break down in 2025?
Across 219 monitored days, 60 fell in the Good band (AQI 0–50) and 6 reached Unhealthy or worse. The worst single day peaked at AQI 190 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 219 days monitored. Median AQI: 64 (Moderate).
Insights: Imperial County, California. EPA monitors recorded a median Air Quality Index of 64 across 219 measured days in 2025, earning a Moderate classification and a Poor health grade. Of those days, 60 (27%) fell in the Good band (AQI 0–50), 132 (60%) registered Moderate readings, and 21 (10%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 108, while the worst single-day peak hit 190 (Unhealthy). Residents averaged about 8.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (121 days), PM10 (52 days), PM2.5 (46 days). Across the 2020–2025 trend window, good days shifted by -34 and the median AQI moved +4 points, placing the multi-year trajectory at stable. Residents and visitors experienced 6 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. 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
27.4%
60 of 219 monitored days
-47.6pp vs 75% target
Max AQI Recorded
190
Unhealthy
Health Grade
Poor
90th-pct AQI 108
Imperial County, Good days share 27.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Imperial County, Unhealthy-or-worse share 2.7%
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 219 monitored days across EPA AQI categories.
Good
60
27%
Moderate
132
60%
USG
21
10%
Unhealthy
6
3%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Imperial County.
- Ozone · 121 days · 55.3%
- PM10 · 52 days · 23.7%
- PM2.5 · 46 days · 21.0%
Health Impact Assessment
Poor
Imperial County's air quality is rated Poor based on 27.4% good air days. There were 6 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 21 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 190. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is Ozone, driving AQI on 121 of 219 monitored days.
5-Year Air Quality Trend
Air quality is stable in Imperial County. Best year: 2023 (104 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 94 | 244 | 26 | 2 | 60 | 166 |
| 2021 | 84 | 252 | 22 | 4 | 60 | 436 |
| 2022 | 86 | 232 | 34 | 5 | 61 | 791 |
| 2023 | 104 | 214 | 37 | 3 | 61 | 506 |
| 2024 | 83 | 233 | 42 | 5 | 63 | 341 |
| 2025 | 60 | 132 | 21 | 6 | 64 | 190 |
How does Imperial County compare?
How Imperial County compares
Good-day share worse than US avg
Imperial County 27.4%
Amador County, California 84.8%
US average 76.5%
Median AQI worse than US avg
Imperial County 64
Amador County, California 40
US average 38
Unhealthy days / yr worse than US avg
Imperial County 6
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 Imperial County.
Clark County, Nevada
AQI 64 · 25.6% good
Harris County, Texas
AQI 63 · 8.8% good
Pinal County, Arizona
AQI 66 · 24.6% good
Kern County, California
AQI 61 · 23.8% good
Bernalillo County, New Mexico
AQI 59 · 23.7% good
Tulare County, California
AQI 59 · 29.7% good
What Imperial County's air means for you
On most days the air here is fine, but Ozone drives 6 unhealthy-or-worse days a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 64 means for exposure. Health guidance
- See how Imperial County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Imperial County with its California neighbours before drawing a conclusion about the region. All of California
Based on 219 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 Imperial County, California? ▼
Imperial County has a median Air Quality Index (AQI) of 64, rated "Moderate." 27.4% of monitored days (60 out of 219) had good air quality in 2025.
What is the main pollutant in Imperial County? ▼
The primary pollutant in Imperial County is Ozone (O3), which was the main AQI driver on 121 days (55% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Imperial County have? ▼
In 2025, Imperial County recorded 6 unhealthy air days (6 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 190.
Is the air quality in Imperial County getting better or worse? ▼
Air quality in Imperial County is stable based on 5-year trends (2020-2025). Best year: 2023 with 104 good days. Worst year: 2025 with 60 good days.
What does AQI 64 mean for health? ▼
Imperial County's median AQI of 64 falls in the "Moderate" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Imperial County compare to other counties in California? ▼
Imperial County has 27.4% 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 Imperial County? ▼
The 90th percentile AQI for Imperial County is 108, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 190 (Unhealthy).
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.