Bad Air Days in Penobscot County, Maine: under 1 a Year

under 1 bad air day a year

Rare: among the cleanest-air counties EPA monitors. Ranked 781 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (67% particle days).

The bad-air season here

Most bad days here fall in May and August and March and June. Averaged over 2016 to 2025.

What actually helps here

Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
On the odd bad day, check AirNow and keep windows shut.

The record for Penobscot

In 2000 to 2009 this county averaged 5 bad days a year; in 2016 to 2025, under 1. The air has improved. The worst recent year was 2025, with 6 bad days on 355 monitored days.

Date	AQI	Main pollutant
2025-05-31	170	PM2.5
2025-05-07	149	PM2.5
2025-03-11	126	PM2.5
2025-08-12	115	Ozone
2025-08-13	115	Ozone

An ordinary day in Penobscot

Across 3,602 monitored days from 2016 to 2025, the air in Penobscot County rated Good on 87% of them, more often than the 72% typical of monitored counties, and Moderate on 13%. The median day sat at AQI 35; one day in ten went above 52.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)51%1,853 days
ozone48%1,724 days
coarse dust (PM10)1%25 days

Penobscot County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	355	299	50	6	1	33	170
2024	362	328	34	0	0	33	84
2023	358	294	64	0	0	35	89
2022	361	324	37	0	0	33	87
2021	362	326	36	0	0	33	100
2020	363	338	25	0	0	33	76
2019	362	336	26	0	0	33	72
2018	365	309	56	0	0	37	97
2017	348	306	42	0	0	34	80
2016	366	265	101	0	0	42	78
2015	364	254	110	0	0	42	100
2014	365	299	66	0	0	36	79
2013	363	301	61	1	0	36	119
2012	366	294	72	0	0	39	87
2011	365	271	94	0	0	39	82
2010	365	299	66	0	0	38	90

*2025 may be a partial year in EPA's file.

Elsewhere in Maine

How this is counted

A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day.