Air Quality Rankings for Puerto Rico (2026)
Puerto Rico has 11 cities tracked by EPA air-quality monitors, with a state-wide 5-year median AQI of 23 — 18 points cleaner than the national average of AQI 41. Juncos, Puerto Rico ranks #1 with the cleanest air (AQI 9, Grade A), while Catano, Puerto Rico sits at the bottom (AQI 42, Grade D).
How Puerto Rico Compares
Puerto Rico has 11 cities tracked by EPA air-quality monitors, with a state-wide 5-year median AQI of 23 — 18 points cleaner than the national average of AQI 41. Juncos, Puerto Rico ranks #1 with the cleanest air (AQI 9, Grade A), while Catano, Puerto Rico sits at the bottom (AQI 42, Grade D). The rankings below are computed from the EPA Air Quality System (AQS), which aggregates daily AQI readings from federally certified monitors into annual averages. Cities are sorted by 5-year median AQI (lowest = cleanest = #1). The 5-year window smooths out year-to-year volatility from weather and wildfire events.
Air quality across Puerto Rico has held roughly steady over the past decade — 6 cities improving, 5 worsening, and 0 stable. That stability makes the state-average ranking a reliable signal of what residents can expect over time.
The dominant pollutant across 5 of 11 Puerto Rico cities is Fine Particulate Matter (PM2.5). PM2.5 (fine particulate matter) is most often driven by combustion sources — vehicle exhaust, industrial emissions, residential wood burning, and increasingly wildfire smoke. It penetrates deep into lung tissue and the bloodstream and is the air pollutant most strongly linked to long-term health impacts. Other Puerto Rico cities report Nitrogen Dioxide (2), Carbon Monoxide (2), Ground-Level Ozone (1) as their dominant concern.
The fastest-improving city in Puerto Rico is Caguas, Puerto Rico, with median AQI falling by 2.3 points per year. Steady improvement at that pace usually reflects fleet turnover (older diesels retiring), upwind power-plant retirements, or tighter regional emissions controls.
The city with the steepest decline is Catano, Puerto Rico, where median AQI is rising by 3.3 points per year. Rapid deterioration in a single city usually points to either wildfire-smoke exposure (in the West) or a new local emissions source — a power plant, port, or freight corridor coming online.
Full Puerto Rico Ranking
| # | City | 5yr Avg AQI | Current AQI | Worst Pollutant | Trend | Grade |
|---|---|---|---|---|---|---|
| 1 | Juncos, Puerto Rico | 9 | 9 | Ozone | Improving | A |
| 2 | Caguas, Puerto Rico | 10 | 6 | NO2 | Improving | A |
| 3 | San Juan, Puerto Rico | 10 | 7 | CO | Improving | A |
| 4 | Bayamon, Puerto Rico | 18 | 22 | CO | Improving | A |
| 5 | Adjuntas, Puerto Rico | 19 | 14 | PM2.5 | Improving | A |
| 6 | Guayama, Puerto Rico | 24 | 15 | PM2.5 | Improving | B |
| 7 | Fajardo, Puerto Rico | 28 | 30 | PM2.5 | Worsening | B |
| 8 | Ponce, Puerto Rico | 29 | 30 | PM10 | Stable | B |
| 9 | Guaynabo, Puerto Rico | 29 | 32 | NO2 | Worsening | C |
| 10 | Mayagnez, Puerto Rico | 31 | 25 | PM2.5 | Worsening | C |
| 11 | Catano, Puerto Rico | 42 | 52 | PM2.5 | Worsening | D |
Air quality data for Puerto Rico is sourced from the EPA Air Quality System (AQS), which monitors outdoor air quality at thousands of stations nationwide.
Frequently Asked Questions
Juncos, Puerto Rico has the best air quality in Puerto Rico with a 5-year average AQI of 9 and a Grade A (91/100). Its dominant pollutant is Ground-Level Ozone and the long-run trend is improving.
Catano, Puerto Rico has the worst air quality in Puerto Rico with a 5-year average AQI of 42 and a Grade D (44/100). Its dominant pollutant is Fine Particulate Matter (PM2.5).
Puerto Rico has 11 cities with EPA air quality monitoring data, covering 2014-2023 of daily AQI measurements aggregated into annual averages.
Puerto Rico's state-wide 5-year median AQI is 23, 18 points cleaner than the national average of AQI 41. Air quality across Puerto Rico has held roughly steady over the past decade — 6 cities improving, 5 worsening, and 0 stable. That stability makes the state-average ranking a reliable signal of what residents can expect over time.
Fine Particulate Matter (PM2.5) is the dominant pollutant in 5 of 11 monitored Puerto Rico cities. PM2.5 (fine particulate matter) is most often driven by combustion sources — vehicle exhaust, industrial emissions, residential wood burning, and increasingly wildfire smoke. It penetrates deep into lung tissue and the bloodstream and is the air pollutant most strongly linked to long-term health impacts.
Puerto Rico cities log an average of 2 days per year at "Unhealthy for Sensitive Groups" or worse, based on EPA monitor data over the last five years. Across all 11 Puerto Rico cities tracked, that totals 84 unhealthy days over the period.
Cities ranked by 5-year average AQI (lower is better). Grades factor in average AQI, trend direction, unhealthy days, and dominant pollutant.
The this entity category groups every U.S. air quality and pollution monitoring entity sharing this attribute. The list above is the data; the paragraphs below explain what the grouping means against the broader the EPA Air Quality System (AQS) distribution and how to read the relative rankings within the category.
For readers using this category as a starting point, the per-entity detail pages linked from the table above carry the underlying the EPA Air Quality System (AQS) data in full. The category-level view is the filter; the per-entity pages are the actual answer.
Source: EPA Outdoor Air Quality Data, 2026.