Spencer County, Indiana air quality history

Daily Air Quality Index summaries from EPA monitors in Spencer, Indiana, 1980–2025.

67%

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 Spencer, Indiana on 365 days. 246 of those days (67%) were in the Good range, and the median daily AQI was 39. That median is about the same as the typical monitored county in Indiana (median 41 across 33 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 365 days. Across the years with fuller monitoring, the share of Good days fell: an average of 99% in 1980–1982 versus 71% in 2023–2025.

Years with fewer than 120 monitored days (2013, 2015, 2016, 2017, 2019, 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)	365	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	365	246	119	0	0	39	59	88	PM2.5
2024	169	132	37	0	0	34	55	68	PM2.5
2023	120	80	39	0	1	43	57	170	PM2.5
2022	111	75	36	0	0	42	57	79	PM2.5
2021	120	78	42	0	0	42	62	89	PM2.5
2020	122	80	42	0	0	42	58	67	PM2.5
2019	117	81	36	0	0	41	58	76	PM2.5
2018	121	72	49	0	0	41	61	87	PM2.5
2017	118	79	39	0	0	43	62	71	PM2.5
2016	118	74	44	0	0	43	59	80	PM2.5
2015	115	63	52	0	0	45	63	78	PM2.5
2014	121	56	65	0	0	52	69	96	PM2.5
2013	118	52	66	0	0	52	66	77	PM2.5
2012	117	54	63	0	0	52	68	74	PM2.5
2011	113	37	76	0	0	55	72	93	PM2.5
2010	116	31	85	0	0	57	71	88	PM2.5
2009	111	36	75	0	0	56	69	90	PM2.5
2008	112	38	74	0	0	55	71	85	PM2.5
2007	113	31	81	1	0	57	83	108	PM2.5
2006	107	37	69	1	0	55	74	125	PM2.5
2005	55	10	42	3	0	62	90	114	PM2.5
2004	58	20	38	0	0	55	75	83	PM2.5
2003	53	14	38	1	0	57	80	107	PM2.5
2002	58	14	44	0	0	57	81	87	PM2.5
2001	270	227	43	0	0	15	61	89	NO2
2000	355	310	40	5	0	15	58	120	NO2
1999	342	338	4	0	0	11	22	80	NO2
1998	148	145	2	1	0	11	17	122	NO2
1995	181	181	0	0	0	18	31	46	NO2
1994	365	362	3	0	0	18	32	77	NO2
1993	360	354	6	0	0	19	32	68	NO2
1992	366	364	2	0	0	19	31	89	NO2
1991	334	331	2	1	0	22	34	117	NO2
1990	364	358	6	0	0	17	28	64	NO2
1989	333	324	9	0	0	17	29	96	NO2
1988	365	355	9	1	0	19	33	104	NO2
1987	348	333	9	6	0	21	37	149	NO2
1986	365	363	2	0	0	19	31	68	NO2
1985	360	357	3	0	0	20	30	59	NO2
1984	364	360	4	0	0	20	31	65	NO2
1983	357	357	0	0	0	18	28	40	NO2
1982	364	363	1	0	0	19	29	88	NO2
1981	361	360	1	0	0	20	31	56	NO2
1980	274	271	3	0	0	20	30	69	NO2

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 Indiana with a similar median AQI in 2025

All monitored counties in Indiana

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem