Fairfield County, Connecticut air quality history

Daily Air Quality Index summaries from EPA monitors in Fairfield, Connecticut, 1980–2025.

65%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

365

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Fairfield, Connecticut on 365 days. 236 of those days (65%) were in the Good range, and the median daily AQI was 44. That median is higher than the typical monitored county in Connecticut (median 41 across 8 counties), and higher than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 170 days. Across the years with fuller monitoring, the share of Good days rose: an average of 21% in 1980–1982 versus 63% in 2023–2025.

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, 2025

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
Fine particles (PM2.5)	170	47%
Ozone	169	46%
Nitrogen dioxide (NO₂)	26	7%

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
2025	365	236	108	19	2	0	44	74	174	PM2.5
2024	366	248	97	18	3	0	42	75	154	Ozone
2023	365	210	135	12	7	1	46	79	242	PM2.5
2022	365	223	120	20	2	0	45	84	156	PM2.5
2021	363	225	119	13	6	0	46	74	185	PM2.5
2020	366	217	136	12	1	0	47	80	161	PM2.5
2019	365	221	123	18	3	0	46	77	161	PM2.5
2018	365	218	126	14	7	0	46	80	185	PM2.5
2017	365	208	141	12	4	0	46	74	179	PM2.5
2016	366	160	183	16	7	0	52	87	185	PM2.5
2015	365	152	183	24	6	0	53	93	177	PM2.5
2014	365	151	200	12	2	0	53	84	164	PM2.5
2013	365	136	204	19	6	0	55	92	185	PM2.5
2012	366	194	143	19	10	0	50	90	179	PM2.5
2011	365	257	88	12	8	0	41	80	190	Ozone
2010	365	204	132	25	4	0	47	93	179	PM2.5
2009	365	220	133	12	0	0	44	80	150	PM2.5
2008	366	172	163	23	8	0	52	93	200	PM2.5
2007	365	171	156	27	10	1	52	108	203	PM2.5
2006	365	250	86	18	9	2	42	90	215	Ozone
2005	365	227	102	20	12	4	44	99	205	Ozone
2004	366	255	88	18	4	1	42	84	205	Ozone
2003	365	228	105	22	7	3	44	95	221	Ozone
2002	365	207	108	18	24	8	46	133	225	NO2
2001	365	192	132	21	15	5	49	109	229	NO2
2000	366	223	112	24	6	1	44	92	220	Ozone
1999	365	212	114	17	14	8	46	105	229	Ozone
1998	365	252	67	28	16	2	42	112	204	Ozone
1997	365	258	71	15	14	7	42	97	240	NO2
1996	366	260	73	23	8	2	42	81	206	NO2
1995	365	258	74	16	10	7	44	97	226	NO2
1994	365	208	112	27	14	4	46	105	225	NO2
1993	365	245	86	14	13	7	43	97	215	NO2
1992	366	275	63	18	7	3	40	90	208	NO2
1991	365	238	79	23	17	8	44	115	228	Ozone
1990	365	222	100	26	10	7	47	108	221	Ozone
1989	365	222	100	21	14	8	46	108	238	Ozone
1988	366	211	90	21	16	28	48	169	259	Ozone
1987	365	211	104	14	19	17	47	150	239	Ozone
1986	365	200	118	25	16	6	49	112	218	NO2
1985	365	164	144	28	15	14	53	143	237	Ozone
1984	366	130	169	27	18	22	57	161	264	CO
1983	365	133	134	33	18	47	58	209	294	Ozone
1982	365	106	176	30	29	24	62	177	272	Ozone
1981	365	91	144	66	37	27	76	185	261	CO
1980	366	33	110	76	82	65	122	219	289	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 Connecticut with a similar median AQI in 2025

All monitored counties in Connecticut

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem