San Juan, Puerto Rico air quality history

Daily Air Quality Index summaries from EPA monitors in San Juan, Puerto Rico, 1981–2021.

100%

Good days in 2020

Median daily AQI, 2020

Days above 100 in 2020

216

Days with an AQI in 2020 (of 366)

In 2020, EPA reported a daily Air Quality Index (AQI) for San Juan, Puerto Rico on 216 days. 216 of those days (100%) were in the Good range, and the median daily AQI was 9. That median is lower than the typical monitored county in Puerto Rico (median 21 across 7 counties), and lower than the typical monitored U.S. county (39). The main pollutant was carbon monoxide (CO) on 216 days. Across the years with fuller monitoring, the share of Good days rose: an average of 52% in 1981–1983 versus 100% in 2017–2020.

EPA did not report an AQI for every day of 2020 here (216 of 366 days). Figures describe monitored days only; seasonal monitoring (for example, ozone measured only in warmer months) can make a county look cleaner or dirtier than a full-year record would.

The most recent year with data for this county is 2021; EPA's files for 2022–2025 contain no row for it, which usually means its monitors stopped reporting.

Years with fewer than 120 monitored days (2021) are shown in the table but left out of comparisons and trend statements.

How the days broke down each year

Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.

Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous

Typical and high-end AQI over time

The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.

Median daily AQI
90th-percentile daily AQI

Main pollutant by day, 2020

On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.

Pollutant	Days as main pollutant	Share of monitored days
Carbon monoxide (CO)	216	100%

Year-by-year data

Annual AQI summary by year
Year	Days with AQI	Good	Moderate	Unhealthy for Sensitive Groups	Unhealthy	Very Unhealthy	Median AQI	90th pct.	Max AQI	Main pollutant
2021	41	41	0	0	0	0	7	9	10	CO
2020	216	216	0	0	0	0	9	32	39	CO
2019	277	277	0	0	0	0	14	17	35	CO
2017	246	246	0	0	0	0	8	17	35	CO
2016	328	327	1	0	0	0	15	19	83	CO
2015	329	321	8	0	0	0	13	23	66	CO
2014	358	358	0	0	0	0	17	23	31	CO
2013	348	348	0	0	0	0	16	23	32	CO
2012	299	281	18	0	0	0	18	38	74	CO
2011	295	282	13	0	0	0	19	35	69	CO
2010	253	253	0	0	0	0	17	20	28	CO
2009	365	350	15	0	0	0	17	34	98	CO
2008	366	344	22	0	0	0	24	43	88	CO
2007	365	293	71	1	0	0	35	55	128	PM2.5
2006	364	266	98	0	0	0	39	56	79	PM2.5
2005	365	266	99	0	0	0	39	58	81	PM2.5
2004	366	312	54	0	0	0	37	54	75	PM2.5
2003	365	211	154	0	0	0	46	62	89	PM2.5
2002	365	244	121	0	0	0	43	57	80	PM2.5
2001	365	228	137	0	0	0	46	58	96	PM2.5
2000	366	189	177	0	0	0	50	61	89	PM2.5
1999	357	119	235	3	0	0	55	78	111	CO
1998	350	253	96	1	0	0	44	57	110	CO
1997	365	315	49	1	0	0	39	52	101	CO
1996	364	262	101	1	0	0	45	60	103	CO
1995	365	286	79	0	0	0	42	55	78	CO
1994	362	325	37	0	0	0	37	51	67	CO
1993	365	307	58	0	0	0	42	54	79	CO
1992	363	297	66	0	0	0	41	54	80	CO
1991	365	269	96	0	0	0	43	56	86	CO
1990	365	322	43	0	0	0	35	52	97	CO
1989	335	261	74	0	0	0	40	56	78	CO
1988	345	288	57	0	0	0	39	54	94	CO
1987	324	302	21	1	0	0	27	45	126	CO
1986	365	220	145	0	0	0	45	60	77	CO
1985	365	162	203	0	0	0	52	64	79	CO
1984	366	258	108	0	0	0	42	60	91	CO
1983	346	181	165	0	0	0	49	70	85	CO
1982	342	142	184	11	3	2	54	79	220	CO
1981	187	116	59	10	2	0	43	77	158	CO

What this data can and can’t tell you

It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.

It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.

Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.

Counties in Puerto Rico with a similar median AQI in 2020

Juncos

All monitored counties in Puerto Rico

Source: U.S. EPA AirData, “Annual AQI by County” files for 1981–2021 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem