Penobscot County, Maine air quality history

Daily Air Quality Index summaries from EPA monitors in Penobscot, Maine, 1980–2025.

84%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

355

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Penobscot, Maine on 355 days. 299 of those days (84%) were in the Good range, and the median daily AQI was 33. That median is about the same as the typical monitored county in Maine (median 34 across 11 counties), and lower than the typical monitored U.S. county (40). The main pollutant was ozone on 187 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 87% in 1980–1982 versus 86% in 2023–2025.

Years with fewer than 120 monitored days (1987) 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, 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
Ozone	187	53%
Fine particles (PM2.5)	162	46%
Coarse particles (PM10)	6	2%

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	355	299	50	5	1	0	33	58	170	Ozone
2024	362	328	34	0	0	0	33	49	84	Ozone
2023	358	294	64	0	0	0	35	55	89	PM2.5
2022	361	324	37	0	0	0	33	51	87	PM2.5
2021	362	326	36	0	0	0	33	50	100	Ozone
2020	363	338	25	0	0	0	33	47	76	Ozone
2019	362	336	26	0	0	0	33	47	72	PM2.5
2018	365	309	56	0	0	0	37	54	97	PM2.5
2017	348	306	42	0	0	0	34	52	80	PM2.5
2016	366	265	101	0	0	0	42	58	78	PM2.5
2015	364	254	110	0	0	0	42	59	100	PM2.5
2014	365	299	66	0	0	0	36	55	79	Ozone
2013	363	301	61	1	0	0	36	57	119	Ozone
2012	366	294	72	0	0	0	39	54	87	PM2.5
2011	365	271	94	0	0	0	39	58	82	PM2.5
2010	365	299	66	0	0	0	38	57	90	PM2.5
2009	364	344	19	1	0	0	31	46	122	Ozone
2008	363	340	20	3	0	0	33	47	105	Ozone
2007	357	325	26	6	0	0	33	50	133	Ozone
2006	365	331	33	1	0	0	33	50	122	Ozone
2005	364	318	44	2	0	0	34	52	108	Ozone
2004	364	328	34	2	0	0	34	50	119	Ozone
2003	354	296	53	4	0	1	37	58	205	Ozone
2002	363	307	46	5	5	0	35	60	179	Ozone
2001	365	306	44	10	5	0	37	64	195	Ozone
2000	365	346	17	2	0	0	34	45	105	Ozone
1999	364	332	22	9	1	0	36	49	169	Ozone
1998	361	324	32	3	2	0	35	51	177	Ozone
1997	360	332	24	4	0	0	34	48	147	Ozone
1996	320	292	24	4	0	0	31	49	108	Ozone
1995	330	292	28	8	2	0	34	54	179	Ozone
1994	356	323	28	5	0	0	35	49	150	Ozone
1993	364	317	39	7	1	0	34	54	151	Ozone
1992	273	247	23	2	1	0	31	47	156	Ozone
1991	276	251	24	0	1	0	28	49	151	Ozone
1990	296	270	23	3	0	0	30	47	136	Ozone
1989	248	239	9	0	0	0	21	39	67	PM10
1988	219	216	3	0	0	0	17	39	57	PM10
1987	105	100	5	0	0	0	21	47	59	PM10
1986	221	205	16	0	0	0	26	47	73	PM10
1985	152	135	17	0	0	0	31	51	62	PM10
1984	178	158	20	0	0	0	30	52	71	PM10
1983	365	347	18	0	0	0	22	43	72	CO
1982	359	323	29	6	1	0	30	51	166	CO
1981	353	307	43	1	2	0	31	55	177	CO
1980	363	306	46	10	1	0	36	60	156	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 Maine with a similar median AQI in 2025

All monitored counties in Maine

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