Median AQI
71
Moderate
Arizona · County air quality · 2025
Maricopa County, Arizona
Median AQI 71 (Moderate). 16.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 71
- Median AQI
- 16.4%
- Good-air days
- 6
- Unhealthy days
- 1%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Maricopa County's air is moderate on balance, among the most polluted counties nationally, a median AQI of 71 with 16.4% of 304 monitored days in the Good band, driven mainly by Ozone.
- 71
- median AQI · Moderate
- 16.4%
- days rated Good
- Ozone
- main pollutant
- 1%
- cleaner than US counties
6 days reached Unhealthy or worse; the worst single reading hit AQI 366.
Data updated July 2026
- Good · 50 d · 16.4%
- Moderate · 219 d · 72.0%
- USG · 29 d · 9.5%
- Unhealthy · 4 d · 1.3%
- Very Unhealthy · 1 d · 0.3%
- Hazardous · 1 d · 0.3%
How did Maricopa County's air break down in 2025?
Across 304 monitored days, 50 fell in the Good band (AQI 0–50) and 6 reached Unhealthy or worse. The worst single day peaked at AQI 366 (Hazardous).
EPA AQS →Air quality data from EPA Air Quality System (2025). 304 days monitored. Median AQI: 71 (Moderate).
Insights: Maricopa County, Arizona. EPA monitors recorded a median Air Quality Index of 71 across 304 measured days in 2025, earning a Moderate classification and a Very Poor health grade. Of those days, 50 (16%) fell in the Good band (AQI 0–50), 219 (72%) registered Moderate readings, and 29 (10%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 101, while the worst single-day peak hit 366 (Hazardous). Residents averaged about 4.9 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (190 days), PM10 (77 days), PM2.5 (37 days). Across the 2020–2025 trend window, good days shifted by +39 and the median AQI moved -41 points, placing the multi-year trajectory at improving. 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: Apache (99.6% good, AQI 14); Cochise (65.6% good, AQI 46); Coconino (62.5% good, AQI 48); Gila (52.0% good, AQI 50); La Paz (68.6% good, AQI 47); Mohave (93.4% good, AQI 19).
Air Quality Summary
Good Days
16.4%
50 of 304 monitored days
-58.5pp vs 75% target
Max AQI Recorded
366
Hazardous
Health Grade
Very Poor
90th-pct AQI 101
Maricopa County, Good days share 16.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Maricopa County, Unhealthy-or-worse share 2.0%
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 304 monitored days across EPA AQI categories.
Good
50
16%
Moderate
219
72%
USG
29
10%
Unhealthy
4
1%
Very Unhealthy
1
0%
Hazardous
1
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Maricopa County.
- Ozone · 190 days · 62.5%
- PM10 · 77 days · 25.3%
- PM2.5 · 37 days · 12.2%
Health Impact Assessment
Very Poor
Maricopa County's air quality is rated Very Poor based on 16.4% good air days. There were 6 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 366, 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 190 of 304 monitored days.
5-Year Air Quality Trend
Air quality is improving in Maricopa County. Best year: 2025 (50 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 11 | 154 | 60 | 66 | 112 | 282 |
| 2021 | 12 | 128 | 91 | 61 | 122 | 297 |
| 2022 | 27 | 242 | 73 | 17 | 75 | 264 |
| 2023 | 41 | 256 | 61 | 7 | 72 | 183 |
| 2024 | 33 | 260 | 65 | 7 | 77 | 261 |
| 2025 | 50 | 219 | 29 | 4 | 71 | 366 |
How does Maricopa County compare?
How Maricopa County compares
Good-day share worse than US avg
Maricopa County 16.4%
Apache County, Arizona 99.6%
US average 76.5%
Median AQI worse than US avg
Maricopa County 71
Apache County, Arizona 14
US average 38
Unhealthy days / yr worse than US avg
Maricopa County 6
Apache County, Arizona 0
US average 0
Other Counties in Arizona
Air quality comparison for nearby counties in Arizona.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Maricopa County.
Dona Ana County, New Mexico
AQI 70 · 19.4% good
El Paso County, Texas
AQI 74 · 12.7% good
Pinal County, Arizona
AQI 66 · 24.6% good
Los Angeles County, California
AQI 77 · 10.9% good
Clark County, Nevada
AQI 64 · 25.6% good
Imperial County, California
AQI 64 · 27.4% good
What Maricopa 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 71 means for exposure. Health guidance
- See how Maricopa County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Maricopa County with its Arizona neighbours before drawing a conclusion about the region. All of Arizona
Based on 304 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 Maricopa County, Arizona? ▼
Maricopa County has a median Air Quality Index (AQI) of 71, rated "Moderate." 16.4% of monitored days (50 out of 304) had good air quality in 2025.
What is the main pollutant in Maricopa County? ▼
The primary pollutant in Maricopa County is Ozone (O3), which was the main AQI driver on 190 days (63% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Maricopa County have? ▼
In 2025, Maricopa County recorded 6 unhealthy air days (4 Unhealthy, 1 Very Unhealthy, 1 Hazardous). The maximum AQI reached 366.
Is the air quality in Maricopa County getting better or worse? ▼
Air quality in Maricopa County is improving based on 5-year trends (2020-2025). Best year: 2025 with 50 good days. Worst year: 2020 with 11 good days.
What does AQI 71 mean for health? ▼
Maricopa County's median AQI of 71 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 Maricopa County compare to other counties in Arizona? ▼
Maricopa County has 16.4% good air days. Nearby counties in Arizona: Apache (99.6% good), Cochise (65.6% good), Coconino (62.5% good), Gila (52.0% good), La Paz (68.6% good), Mohave (93.4% good).
What is the 90th percentile AQI in Maricopa County? ▼
The 90th percentile AQI for Maricopa County is 101, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 366 (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.
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.