Rock County, Minnesota air quality history

Daily Air Quality Index summaries from EPA monitors in Rock, Minnesota, 2002–2015.

68%

Good days in 2004

Median daily AQI, 2004

Days above 100 in 2004

120

Days with an AQI in 2004 (of 366)

In 2004, EPA reported a daily Air Quality Index (AQI) for Rock, Minnesota on 120 days. 81 of those days (68%) were in the Good range, and the median daily AQI was 38. That median is about the same as the typical monitored county in Minnesota (median 39 across 16 counties), and lower than the typical monitored U.S. county (42). The main pollutant was fine particles (PM2.5) on 120 days.

EPA did not report an AQI for every day of 2004 here (120 of 366 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.

The most recent year with data for this county is 2015; EPA's files for 2016–2025 contain no row for it, which usually means its monitors stopped reporting.

Years with fewer than 120 monitored days (2010, 2011, 2012, 2013, 2014, 2015…) 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, 2004

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	Median AQI	90th pct.	Max AQI	Main pollutant
2015	119	100	19	0	29	52	85	PM2.5
2014	117	97	19	1	29	55	101	PM2.5
2013	117	89	28	0	30	59	81	PM2.5
2012	117	89	28	0	33	56	69	PM2.5
2011	100	83	17	0	32	56	69	PM2.5
2010	108	79	29	0	34	61	81	PM2.5
2009	102	76	26	0	33	61	99	PM2.5
2008	112	81	31	0	37	57	86	PM2.5
2007	112	79	33	0	39	61	91	PM2.5
2006	111	84	27	0	32	56	82	PM2.5
2005	116	83	33	0	36	66	85	PM2.5
2004	120	81	39	0	38	68	94	PM2.5
2003	118	73	45	0	37	63	84	PM2.5
2002	50	34	16	0	33	60	72	PM2.5

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 Minnesota

Source: U.S. EPA AirData, “Annual AQI by County” files for 2002–2015 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem