Fremont County, Colorado air quality history

Daily Air Quality Index summaries from EPA monitors in Fremont, Colorado, 1987–2025.

93%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

362

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Fremont, Colorado on 362 days. 338 of those days (93%) were in the Good range, and the median daily AQI was 23. That median is lower than the typical monitored county in Colorado (median 46 across 27 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 263 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 98% in 1988–1990 versus 97% in 2023–2025.

Years with fewer than 120 monitored days (2017, 2018, 2019, 2020, 2021, 2022…) 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
Fine particles (PM2.5)	263	73%
Coarse particles (PM10)	99	27%

Year-by-year data

Annual AQI summary by year
Year	Days with AQI	Good	Moderate	Unhealthy for Sensitive Groups	Median AQI	90th pct.	Max AQI	Main pollutant
2025	362	338	24	0	23	45	77	PM2.5
2024	362	354	8	0	13	29	59	PM10
2023	163	162	1	0	12	21	71	PM10
2022	118	115	3	0	12	26	77	PM10
2021	86	85	1	0	15	28	62	PM10
2020	17	17	0	0	11	20	27	PM10
2019	32	32	0	0	13	23	29	PM10
2018	20	20	0	0	15	20	36	PM10
2017	39	39	0	0	11	28	44	PM10
2016	52	52	0	0	14	24	50	PM10
2015	57	57	0	0	11	22	37	PM10
2014	59	58	1	0	15	27	51	PM10
2013	62	60	2	0	16	34	78	PM10
2012	57	56	1	0	15	30	54	PM10
2011	57	55	2	0	15	27	59	PM10
2010	54	54	0	0	14	22	29	PM10
2009	59	59	0	0	13	25	35	PM10
2008	58	58	0	0	14	27	50	PM10
2007	56	56	0	0	17	23	29	PM10
2006	57	57	0	0	16	25	50	PM10
2005	54	54	0	0	17	27	31	PM10
2004	60	60	0	0	13	21	30	PM10
2003	58	58	0	0	13	23	28	PM10
2002	57	57	0	0	16	28	39	PM10
2001	59	59	0	0	13	25	37	PM10
2000	60	59	1	0	15	20	90	PM10
1999	59	57	2	0	11	28	85	PM10
1998	58	57	1	0	14	26	60	PM10
1997	55	55	0	0	12	29	38	PM10
1996	46	46	0	0	15	27	43	PM10
1995	290	288	2	0	15	30	56	PM10
1994	332	325	7	0	17	35	62	PM10
1993	320	316	4	0	17	31	62	PM10
1992	344	342	2	0	18	31	62	PM10
1991	336	318	18	0	18	41	74	PM10
1990	330	330	0	0	16	31	45	PM10
1989	344	337	7	0	19	36	88	PM10
1988	335	323	11	1	18	37	109	PM10
1987	6	6	0	0	14	25	25	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.

Counties in Colorado with a similar median AQI in 2025

All monitored counties in Colorado

Source: U.S. EPA AirData, “Annual AQI by County” files for 1987–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem