Powell County, Montana air quality history

Daily Air Quality Index summaries from EPA monitors in Powell, Montana, 1985–2025.

92%

Good days in 2015

Median daily AQI, 2015

Days above 100 in 2015

120

Days with an AQI in 2015 (of 365)

In 2015, EPA reported a daily Air Quality Index (AQI) for Powell, Montana on 120 days. 111 of those days (92%) were in the Good range, and the median daily AQI was 11. That median is lower than the typical monitored county in Montana (median 37 across 17 counties), and lower than the typical monitored U.S. county (41). The main pollutant was fine particles (PM2.5) on 120 days.

EPA did not report an AQI for every day of 2015 here (120 of 365 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.

Years with fewer than 120 monitored days (2020, 2021, 2022, 2023, 2024, 2025…) 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, 2015

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)	120	100%

Year-by-year data

Annual AQI summary by year
Year	Days with AQI	Good	Moderate	Unhealthy for Sensitive Groups	Unhealthy	Median AQI	90th pct.	Max AQI	Main pollutant
2025	95	90	5	0	0	13	33	75	PM2.5
2024	114	101	11	2	0	12	52	144	PM2.5
2023	109	100	7	2	0	14	47	115	PM2.5
2022	114	105	8	1	0	12	46	104	PM2.5
2021	117	101	13	3	0	12	63	133	PM2.5
2020	33	33	0	0	0	3	8	14	PM2.5
2019	109	105	4	0	0	12	33	84	PM2.5
2018	113	104	9	0	0	12	45	93	PM2.5
2017	105	91	13	1	0	9	61	143	PM2.5
2016	119	116	3	0	0	10	24	58	PM2.5
2015	120	111	7	0	2	11	41	178	PM2.5
2014	118	110	7	1	0	10	43	119	PM2.5
2013	119	113	6	0	0	9	34	69	PM2.5
2012	118	101	16	1	0	12	65	108	PM2.5
2011	108	103	5	0	0	11	33	72	PM2.5
2010	111	106	5	0	0	13	27	76	PM2.5
2009	117	116	1	0	0	12	34	51	PM2.5
2008	112	111	1	0	0	12	34	56	PM2.5
2007	109	91	16	2	0	12	69	147	PM2.5
2006	116	110	6	0	0	12	40	79	PM2.5
2005	120	113	7	0	0	11	33	87	PM2.5
2004	114	110	4	0	0	10	29	56	PM2.5
2003	107	103	4	0	0	11	29	70	PM2.5
2002	114	113	1	0	0	14	31	57	PM2.5
2001	112	107	5	0	0	13	39	61	PM2.5
2000	61	56	5	0	0	17	42	69	PM2.5
1987	32	32	0	0	0	12	22	29	PM10
1986	51	49	2	0	0	14	29	61	PM10
1985	27	25	2	0	0	19	44	58	PM10

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.

All monitored counties in Montana

Source: U.S. EPA AirData, “Annual AQI by County” files for 1985–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem