Median AQI
18
Good
Puerto Rico · County air quality · 2025
Guayama County, Puerto Rico
Median AQI 18 (Good). 100.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 18
- Median AQI
- 100.0%
- Good-air days
- 0
- Unhealthy days
- 96%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Guayama County's air is good on balance, among the cleanest 5% of US counties, a median AQI of 18 with 100.0% of 28 monitored days in the Good band, driven mainly by PM10.
- 18
- median AQI · Good
- 100.0%
- days rated Good
- PM10
- main pollutant
- 96%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 40.
Data updated July 2026
- Good · 28 d · 100.0%
How did Guayama County's air break down in 2025?
Across 28 monitored days, 28 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 40 (Good).
EPA AQS →Air quality data from EPA Air Quality System (2025). 28 days monitored. Median AQI: 18 (Good).
Insights: Guayama County, Puerto Rico. EPA monitors recorded a median Air Quality Index of 18 across 28 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 28 (100%) fell in the Good band (AQI 0–50), 0 (0%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 38, while the worst single-day peak hit 40 (Good). Residents averaged about 30.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM10 (28 days). Across the 2020–2025 trend window, good days shifted by +2 and the median AQI moved -13 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 40, good but never Unhealthy. 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); Guaynabo (86.0% good, AQI 30); Mayagnez (96.9% good, AQI 12).
Air Quality Summary
Good Days
100.0%
28 of 28 monitored days
25.0pp vs 75% target
Max AQI Recorded
40
Good
Health Grade
Excellent
90th-pct AQI 38
Guayama County, Good days share 100.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Guayama County, Unhealthy-or-worse share 0.0%
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 28 monitored days across EPA AQI categories.
Good
28
100%
Moderate
0
0%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Guayama County.
- PM10 · 28 days · 100.0%
Health Impact Assessment
Excellent
Guayama County's air quality is rated Excellent based on 100.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 100.0% of monitored days in 2025, with a median AQI of 18. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM10, driving AQI on 28 of 28 monitored days.
5-Year Air Quality Trend
Air quality is improving in Guayama County. Best year: 2022 (65 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 26 | 8 | 0 | 0 | 31 | 82 |
| 2021 | 39 | 15 | 0 | 0 | 28 | 77 |
| 2022 | 65 | 2 | 0 | 0 | 16 | 67 |
| 2023 | 57 | 2 | 0 | 0 | 15 | 55 |
| 2024 | 51 | 1 | 0 | 0 | 15 | 53 |
| 2025 | 28 | 0 | 0 | 0 | 18 | 40 |
How does Guayama County compare?
How Guayama County compares
Good-day share better than US avg
Guayama County 100.0%
Bayamon County, Puerto Rico 88.5%
US average 76.5%
Median AQI better than US avg
Guayama County 18
Bayamon County, Puerto Rico 29
US average 38
Unhealthy days / yr about average
Guayama County 0
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 Guayama County.
Garfield County, Washington
AQI 18 · 95.9% good
Lewis County, Washington
AQI 18 · 93.3% good
Marquette County, Michigan
AQI 18 · 87.0% good
Phillips County, Montana
AQI 18 · 94.2% good
St John County, Virgin Islands
AQI 18 · 100.0% good
Adams County, Washington
AQI 19 · 94.7% good
What Guayama County's air means for you
The air here stays in the breathable range year-round, with PM10 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM10 days, the guide explains what a median of 18 means for exposure. Health guidance
- See how Guayama County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Guayama County with its Puerto Rico neighbours before drawing a conclusion about the region. All of Puerto Rico
Based on 28 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 Guayama County, Puerto Rico? ▼
Guayama County has a median Air Quality Index (AQI) of 18, rated "Good." 100.0% of monitored days (28 out of 28) had good air quality in 2025.
What is the main pollutant in Guayama County? ▼
The primary pollutant in Guayama County is Coarse Particles (PM10), which was the main AQI driver on 28 days (100% of monitored days). Irritates airways and can aggravate asthma and bronchitis.
How many unhealthy air days does Guayama County have? ▼
In 2025, Guayama County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 40.
Is the air quality in Guayama County getting better or worse? ▼
Air quality in Guayama County is improving based on 5-year trends (2020-2025). Best year: 2022 with 65 good days. Worst year: 2020 with 26 good days.
What does AQI 18 mean for health? ▼
Guayama County's median AQI of 18 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 Guayama County compare to other counties in Puerto Rico? ▼
Guayama County has 100.0% good air days. Nearby counties in Puerto Rico: Bayamon (88.5% good), Caguas (94.3% good), Catano (64.6% good), Fajardo (85.7% good), Guaynabo (86.0% good), Mayagnez (96.9% good).
What is the 90th percentile AQI in Guayama County? ▼
The 90th percentile AQI for Guayama County is 38, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 40 (Good).
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.