Natrona County, Wyoming air quality history

Daily Air Quality Index summaries from EPA monitors in Natrona, Wyoming, 1985–2025.

86%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

365

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Natrona, Wyoming on 365 days. 315 of those days (86%) were in the Good range, and the median daily AQI was 42. That median is about the same as the typical monitored county in Wyoming (median 41 across 17 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 348 days. Across the years with fuller monitoring, the share of Good days fell: an average of 92% in 2008–2011 versus 86% in 2023–2025.

Years with fewer than 120 monitored days (2003, 2004, 2005, 2006, 2007, 2009…) 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	348	95%
Fine particles (PM2.5)	16	4%
Nitrogen dioxide (NO₂)	1	<1%

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	365	315	50	0	42	54	76	Ozone
2024	366	282	78	6	43	67	136	Ozone
2023	365	344	20	1	42	49	102	Ozone
2022	365	317	48	0	42	54	97	Ozone
2021	365	282	77	6	42	71	125	Ozone
2020	366	316	46	4	42	54	124	Ozone
2019	364	327	37	0	42	51	74	Ozone
2018	365	286	79	0	42	58	90	Ozone
2017	365	286	77	2	44	61	137	Ozone
2016	366	330	36	0	41	50	80	Ozone
2015	365	329	36	0	41	50	96	Ozone
2014	365	327	38	0	41	51	77	Ozone
2013	365	301	62	2	42	58	133	Ozone
2012	365	307	57	1	31	56	103	Ozone
2011	212	176	36	0	33	58	77	Ozone
2010	121	111	10	0	22	43	60	PM2.5
2009	119	116	3	0	17	34	70	PM2.5
2008	120	120	0	0	14	30	43	PM10
2007	115	115	0	0	18	26	42	PM10
2006	88	85	3	0	17	31	66	PM10
2005	91	91	0	0	14	26	41	PM10
2004	94	93	1	0	14	27	53	PM10
2003	57	54	2	1	16	38	120	PM10
2002	54	54	0	0	13	28	41	PM10
2001	56	56	0	0	16	29	48	PM10
2000	57	57	0	0	13	28	42	PM10
1999	51	50	1	0	15	27	76	PM10
1998	58	58	0	0	15	29	44	PM10
1997	56	56	0	0	11	27	31	PM10
1996	56	56	0	0	17	31	47	PM10
1995	58	57	1	0	17	30	65	PM10
1994	47	47	0	0	15	31	49	PM10
1993	59	59	0	0	16	25	41	PM10
1992	56	56	0	0	19	35	44	PM10
1991	9	9	0	0	12	34	34	PM10
1987	31	31	0	0	27	40	47	PM10
1986	59	58	1	0	19	34	55	PM10
1985	2	2	0	0	23	23	23	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 Wyoming with a similar median AQI in 2025

All monitored counties in Wyoming

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