Cascade County, Montana air quality history

Daily Air Quality Index summaries from EPA monitors in Cascade, Montana, 1980–2024.

50%

Good days in 2023

Median daily AQI, 2023

Days above 100 in 2023

351

Days with an AQI in 2023 (of 365)

In 2023, EPA reported a daily Air Quality Index (AQI) for Cascade, Montana on 351 days. 176 of those days (50%) were in the Good range, and the median daily AQI was 50. That median is higher than the typical monitored county in Montana (median 38 across 19 counties), and higher than the typical monitored U.S. county (43). The main pollutant was fine particles (PM2.5) on 351 days. Across the years with fuller monitoring, the share of Good days fell: an average of 91% in 1980–1982 versus 74% in 2021–2023.

The most recent year with data for this county is 2024; EPA's files for 2025–2025 contain no row for it, which usually means its monitors stopped reporting.

Years with fewer than 120 monitored days (2024) 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, 2023

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)	351	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
2024	87	52	35	0	0	0	46	58	74	PM2.5
2023	351	176	169	5	1	0	50	65	170	PM2.5
2022	359	323	34	2	0	0	23	51	128	PM2.5
2021	365	296	58	9	2	0	27	62	160	PM2.5
2020	359	314	42	3	0	0	24	54	115	PM2.5
2019	363	326	36	1	0	0	28	51	106	PM2.5
2018	360	303	51	5	1	0	33	56	166	PM2.5
2017	345	241	103	1	0	0	38	60	105	PM2.5
2016	356	319	37	0	0	0	33	51	75	PM2.5
2015	347	271	67	3	6	0	35	59	170	PM2.5
2014	330	222	106	1	1	0	38	61	155	PM2.5
2013	337	262	75	0	0	0	35	56	74	PM2.5
2012	360	231	126	3	0	0	42	62	132	PM2.5
2011	347	227	120	0	0	0	43	59	84	PM2.5
2010	365	260	105	0	0	0	39	59	99	PM2.5
2009	365	229	136	0	0	0	42	59	72	PM2.5
2008	365	321	44	0	0	0	17	52	71	PM2.5
2007	365	343	19	3	0	0	8	37	140	CO
2006	365	343	22	0	0	0	9	36	80	CO
2005	365	340	25	0	0	0	9	42	71	CO
2004	366	358	8	0	0	0	9	28	73	CO
2003	353	329	21	2	1	0	11	37	155	CO
2002	341	329	12	0	0	0	12	32	69	CO
2001	353	337	16	0	0	0	15	38	96	CO
2000	361	337	22	2	0	0	15	39	113	CO
1999	353	353	0	0	0	0	11	23	41	CO
1998	353	351	2	0	0	0	16	31	59	CO
1997	365	358	7	0	0	0	16	30	80	CO
1996	342	338	4	0	0	0	18	33	91	CO
1995	347	336	11	0	0	0	18	35	85	CO
1994	361	354	7	0	0	0	18	34	80	CO
1993	365	350	15	0	0	0	19	39	88	CO
1992	355	342	13	0	0	0	23	41	72	CO
1991	356	335	19	2	0	0	23	42	116	CO
1990	350	340	10	0	0	0	25	40	79	CO
1989	346	320	26	0	0	0	24	43	92	CO
1988	358	303	53	2	0	0	33	55	125	CO
1987	335	293	38	4	0	0	26	55	142	CO
1986	365	315	49	1	0	0	27	56	111	CO
1985	338	305	33	0	0	0	28	50	88	CO
1984	334	306	26	0	2	0	26	48	186	CO
1983	265	236	27	2	0	0	16	53	115	CO
1982	246	245	1	0	0	0	13	30	60	CO
1981	356	321	33	0	1	1	40	50	230	Ozone
1980	327	277	34	15	0	1	33	74	249	Ozone

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 Montana with a similar median AQI in 2023

Powder River

All monitored counties in Montana

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2024 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem