Median AQI
12
Good
Puerto Rico · County air quality · 2025
Mayagnez County, Puerto Rico
Median AQI 12 (Good). 96.9% of monitored days rated Good, direct from EPA Air Quality System stations.
- 12
- Median AQI
- 96.9%
- Good-air days
- 2
- Unhealthy days
- 93%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Mayagnez County's air is good on balance, among the cleanest 10% of US counties, a median AQI of 12 with 96.9% of 163 monitored days in the Good band, driven mainly by Ozone.
- 12
- median AQI · Good
- 96.9%
- days rated Good
- Ozone
- main pollutant
- 93%
- cleaner than US counties
2 days reached Unhealthy or worse; the worst single reading hit AQI 350.
Data updated July 2026
- Good · 158 d · 96.9%
- Moderate · 1 d · 0.6%
- USG · 2 d · 1.2%
- Very Unhealthy · 1 d · 0.6%
- Hazardous · 1 d · 0.6%
How did Mayagnez County's air break down in 2025?
Across 163 monitored days, 158 fell in the Good band (AQI 0–50) and 2 reached Unhealthy or worse. The worst single day peaked at AQI 350 (Hazardous).
EPA AQS →Air quality data from EPA Air Quality System (2025). 163 days monitored. Median AQI: 12 (Good).
Insights: Mayagnez County, Puerto Rico. EPA monitors recorded a median Air Quality Index of 12 across 163 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 158 (97%) fell in the Good band (AQI 0–50), 1 (1%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 28, while the worst single-day peak hit 350 (Hazardous). Residents averaged about 29.1 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (163 days). Across the 2020–2025 trend window, good days shifted by -108 and the median AQI moved -10 points, placing the multi-year trajectory at improving. Residents and visitors experienced 2 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Bayamon (88.5% good, AQI 29); Caguas (94.3% good, AQI 3); Catano (64.6% good, AQI 44); Fajardo (85.7% good, AQI 29); Guayama (100.0% good, AQI 18); Guaynabo (86.0% good, AQI 30).
Air Quality Summary
Good Days
96.9%
158 of 163 monitored days
21.9pp vs 75% target
Max AQI Recorded
350
Hazardous
Health Grade
Excellent
90th-pct AQI 28
Mayagnez County, Good days share 96.9%
National avg
Share of monitored days at AQI 0-50 (Good band).
Mayagnez County, Unhealthy-or-worse share 1.2%
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 163 monitored days across EPA AQI categories.
Good
158
97%
Moderate
1
1%
USG
2
1%
Unhealthy
0
0%
Very Unhealthy
1
1%
Hazardous
1
1%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Mayagnez County.
- Ozone · 163 days · 100.0%
Health Impact Assessment
Excellent
Mayagnez County's air quality is rated Excellent based on 96.9% good air days. There were 2 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 350, 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 163 of 163 monitored days.
5-Year Air Quality Trend
Air quality is improving in Mayagnez County. Best year: 2024 (341 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 266 | 49 | 1 | 1 | 22 | 396 |
| 2021 | 231 | 101 | 2 | 0 | 38 | 142 |
| 2022 | 235 | 81 | 4 | 1 | 38 | 155 |
| 2023 | 254 | 31 | 0 | 0 | 25 | 64 |
| 2024 | 341 | 0 | 0 | 0 | 11 | 39 |
| 2025 | 158 | 1 | 2 | 0 | 12 | 350 |
How does Mayagnez County compare?
How Mayagnez County compares
Good-day share better than US avg
Mayagnez County 96.9%
Bayamon County, Puerto Rico 88.5%
US average 76.5%
Median AQI better than US avg
Mayagnez County 12
Bayamon County, Puerto Rico 29
US average 38
Unhealthy days / yr worse than US avg
Mayagnez County 2
Bayamon County, Puerto Rico 0
US average 0
Other Counties in Puerto Rico
Air quality comparison for nearby counties in Puerto Rico.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Mayagnez County.
Beaverhead County, Montana
AQI 12 · 100.0% good
Columbiana County, Ohio
AQI 12 · 100.0% good
Cook County, Minnesota
AQI 12 · 100.0% good
Navajo County, Arizona
AQI 12 · 99.6% good
Socorro County, New Mexico
AQI 12 · 100.0% good
Windham County, Vermont
AQI 12 · 100.0% good
What Mayagnez County's air means for you
On most days the air here is fine, but Ozone drives 2 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 12 means for exposure. Health guidance
- See how Mayagnez County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Mayagnez County with its Puerto Rico neighbours before drawing a conclusion about the region. All of Puerto Rico
Based on 163 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 Mayagnez County, Puerto Rico? ▼
Mayagnez County has a median Air Quality Index (AQI) of 12, rated "Good." 96.9% of monitored days (158 out of 163) had good air quality in 2025.
What is the main pollutant in Mayagnez County? ▼
The primary pollutant in Mayagnez County is Ozone (O3), which was the main AQI driver on 163 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Mayagnez County have? ▼
In 2025, Mayagnez County recorded 2 unhealthy air days (0 Unhealthy, 1 Very Unhealthy, 1 Hazardous). The maximum AQI reached 350.
Is the air quality in Mayagnez County getting better or worse? ▼
Air quality in Mayagnez County is improving based on 5-year trends (2020-2025). Best year: 2024 with 341 good days. Worst year: 2025 with 158 good days.
What does AQI 12 mean for health? ▼
Mayagnez County's median AQI of 12 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 Mayagnez County compare to other counties in Puerto Rico? ▼
Mayagnez County has 96.9% good air days. Nearby counties in Puerto Rico: Bayamon (88.5% good), Caguas (94.3% good), Catano (64.6% good), Fajardo (85.7% good), Guayama (100.0% good), Guaynabo (86.0% good).
What is the 90th percentile AQI in Mayagnez County? ▼
The 90th percentile AQI for Mayagnez County is 28, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 350 (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.