Median AQI
64
Moderate
California · County air quality · 2025
Imperial County, California
Median AQI 64 (Moderate). 27.7% of monitored days rated Good, direct from EPA Air Quality System stations.
- 64
- Median AQI
- 27.7%
- Good-air days
- 10
- Unhealthy days
- 1%
- Cleaner than US counties
Imperial County's 2025 annual median AQI is 64 (Moderate), with 27.7% Good days
According to the U.S. EPA Air Quality System, Imperial County, California posted a 2025 median AQI of 64 (Moderate) across 365 monitored days, with 27.7% rated Good and 10 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Imperial County's 27.7% Good-day share places it cleaner than 1% of US counties in 2025.
- Closest median-AQI peer
- Tulare County (24.1% Good, median AQI 64) is the closest nationwide median-AQI peer to Imperial County.
- 2020–2025 trend
- Imperial County's floor-qualifying Good-day share is stable from 2020 to 2025 (25.7% → 27.7%).
- Median AQI
- Median AQI: 64
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 27.7% of 365 monitored days in the Good band, driven mainly by Ozone.
- 64
- median AQI · Moderate
- 27.7%
- days rated Good
- Ozone
- main pollutant
- 1%
- cleaner than US counties
10 days reached Unhealthy or worse; the worst single reading hit AQI 426.
Annual release change
What changed in the 2025 EPA annual release
- Imperial County's peak single-day AQI rose from 341 to 426 between the 2024 and 2025 EPA annual releases, a change of +85 points.
- Imperial County's Good-day share rose from 22.7% to 27.7% between the 2024 and 2025 EPA annual releases, a change of +5.0 percentage points.
- Imperial County's Unhealthy-category days rose from 5 to 9 between the 2024 and 2025 EPA annual releases, a change of +4 days.
Data updated August 2026
- Good · 101 d · 27.7%
- Moderate · 220 d · 60.3%
- USG · 34 d · 9.3%
- Unhealthy · 9 d · 2.5%
- Hazardous · 1 d · 0.3%
How did Imperial County's air break down in 2025?
Across 365 monitored days, 101 fell in the Good band (AQI 0–50) and 10 reached Unhealthy or worse. The worst single day peaked at AQI 426 (Hazardous).
EPA AQS →Air quality data from EPA Air Quality System (2025). 365 days monitored. Median AQI: 64 (Moderate).
Insights: Imperial County, California. EPA monitors recorded a median Air Quality Index of 64 across 365 measured days in 2025, earning a Moderate classification and a Poor health grade. Of those days, 101 (28%) fell in the Good band (AQI 0–50), 220 (60%) registered Moderate readings, and 34 (9%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 108, while the worst single-day peak hit 426 (Hazardous). Residents averaged about 8.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (192 days), PM10 (100 days), PM2.5 (72 days), NO2 (1 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +2.0 points and the median AQI moved +4 points, placing the multi-year trajectory at stable. The annual record contains 10 days at Unhealthy or worse. On those days, the EPA recommends that sensitive groups limit prolonged outdoor exertion. 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
27.7%
101 of 365 monitored days
-47.3pp vs 75% target
Max AQI Recorded
426
Hazardous
Health Grade
Poor
90th-pct AQI 108
Imperial County, Good days share 27.7%
National avg
Share of monitored days at AQI 0-50 (Good band).
Imperial County, Unhealthy-or-worse share 27.4%
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 365 monitored days across EPA AQI categories.
Good
101
28%
Moderate
220
60%
USG
34
9%
Unhealthy
9
2%
Very Unhealthy
0
0%
Hazardous
1
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Imperial County.
- Ozone · 192 days · 52.6%
- PM10 · 100 days · 27.4%
- PM2.5 · 72 days · 19.7%
- NO₂ · 1 days · 0.3%
Health Impact Assessment
Poor
Imperial County's air quality is rated Poor based on 27.7% good air days. There were 10 unhealthy days in 2025 when outdoor activity should be limited.
Air quality posed significant health risk in 2025. Sensitive groups, including people with asthma, COPD, cardiovascular conditions, children, pregnant women, and adults over 65, should monitor AirNow.gov alerts and limit outdoor activity on Unhealthy (AQI 151+) and Very Unhealthy (201+) days. Peak readings reached AQI 426, well into the Hazardous range.
Sensitive group advisory
People with asthma, COPD, heart disease, children, pregnant women, and adults 65+ should follow EPA AQI alerts daily and limit outdoor exertion when AQI exceeds 100. Real-time conditions: airnow.gov.
The dominant pollutant is Ozone, driving AQI on 192 of 365 monitored days.
5-Year Air Quality Trend
Air quality is stable in Imperial County. Highest Good-day share: 2023 (29.1%, 104 of 365 monitored 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 | 101 | 220 | 34 | 9 | 64 | 426 |
How does Imperial County compare?
How Imperial County compares
Good-day share worse than typical
Imperial County 27.7%
Tulare County, California 24.1%
Typical US county 76.0%
Median AQI worse than typical
Imperial County 64
Tulare County, California 64
Typical US county 39
Unhealthy days / yr worse than typical
Imperial County 10
Tulare County, California 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Imperial County (64), not geographic neighbors.
Tulare County, California
Median AQI 64 · 24.1% Good-day share
Harris County, Texas
Median AQI 62 · 11.0% Good-day share
Clark County, Nevada
Median AQI 61 · 31.0% Good-day share
Dona Ana County, New Mexico
Median AQI 61 · 27.4% Good-day share
Fresno County, California
Median AQI 61 · 28.8% Good-day share
Pinal County, Arizona
Median AQI 67 · 17.0% 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).
Bernalillo County, New Mexico
26.6% Good-day share · median AQI 58
Salt Lake County, Utah
33.1% Good-day share · median AQI 57
Pima County, Arizona
33.7% Good-day share · median AQI 54
Inyo County, California
37.3% Good-day share · median AQI 55
Kern County, California
17.5% Good-day share · median AQI 70
San Bernardino County, California
12.6% Good-day share · median AQI 77
California counties on the map
Geographic containment only, other monitored counties in California, independent of AQI or pollutant match.
What Imperial County's air means for you
On most days the air here is fine, but Ozone drives 10 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 365 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 Imperial County, California? ▼
Imperial County has a median Air Quality Index (AQI) of 64, rated "Moderate." 27.7% of monitored days (101 out of 365) 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 192 days (53% 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 10 unhealthy air days (9 Unhealthy, 0 Very Unhealthy, 1 Hazardous). The maximum AQI reached 426.
Is the air quality in Imperial County getting better or worse? ▼
Air quality in Imperial 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: 2023 at 29.1% (104 of 365 days). Lowest qualifying Good-day share: 2024 at 22.9% (83 of 366 days).
What does AQI 64 mean for health? ▼
Imperial County's median AQI of 64 falls in the "Moderate" category. See the AQI category guide for what each range means for health.
How does Imperial County compare to other counties in California? ▼
Imperial County has 27.7% 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 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 426 (Hazardous).
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 Imperial 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.