EnviroNearby

Walworth County, Wisconsin air quality history

Daily Air Quality Index summaries from EPA monitors in Walworth, Wisconsin, 1980–2025.

79%
Good days in 2025
42
Median daily AQI, 2025
3
Days above 100 in 2025
199
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Walworth, Wisconsin on 199 days. 158 of those days (79%) were in the Good range, and the median daily AQI was 42. That median is higher than the typical monitored county in Wisconsin (median 38 across 29 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 199 days. Across the years with fuller monitoring, the share of Good days rose: an average of 73% in 1980–1987 versus 76% in 2023–2025.

EPA did not report an AQI for every day of 2025 here (199 of 365 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.

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.

Share of monitored days in each AQI category, by year0%25%50%75%100%1980: Good 97 of 146 days1980: Moderate 31 of 146 days1980: Unhealthy for Sensitive Groups 12 of 146 days1980: Unhealthy 6 of 146 days19801981: Good 143 of 196 days1981: Moderate 35 of 196 days1981: Unhealthy for Sensitive Groups 16 of 196 days1981: Unhealthy 2 of 196 days1987: Good 112 of 139 days1987: Moderate 18 of 139 days1987: Unhealthy for Sensitive Groups 9 of 139 days1988: Good 171 of 275 days1988: Moderate 45 of 275 days1988: Unhealthy for Sensitive Groups 39 of 275 days1988: Unhealthy 18 of 275 days1988: Very Unhealthy 2 of 275 days1989: Good 187 of 273 days1989: Moderate 59 of 273 days1989: Unhealthy for Sensitive Groups 22 of 273 days1989: Unhealthy 4 of 273 days1989: Very Unhealthy 1 of 273 days1990: Good 209 of 264 days1990: Moderate 48 of 264 days1990: Unhealthy for Sensitive Groups 6 of 264 days1990: Unhealthy 1 of 264 days19901991: Good 181 of 270 days1991: Moderate 44 of 270 days1991: Unhealthy for Sensitive Groups 32 of 270 days1991: Unhealthy 12 of 270 days1991: Very Unhealthy 1 of 270 days1992: Good 228 of 270 days1992: Moderate 28 of 270 days1992: Unhealthy for Sensitive Groups 10 of 270 days1992: Unhealthy 4 of 270 days1993: Good 184 of 225 days1993: Moderate 33 of 225 days1993: Unhealthy for Sensitive Groups 8 of 225 days1994: Good 127 of 182 days1994: Moderate 45 of 182 days1994: Unhealthy for Sensitive Groups 8 of 182 days1994: Unhealthy 2 of 182 days1995: Good 115 of 175 days1995: Moderate 38 of 175 days1995: Unhealthy for Sensitive Groups 18 of 175 days1995: Unhealthy 4 of 175 days19951996: Good 129 of 175 days1996: Moderate 34 of 175 days1996: Unhealthy for Sensitive Groups 10 of 175 days1996: Unhealthy 2 of 175 days1997: Good 128 of 179 days1997: Moderate 33 of 179 days1997: Unhealthy for Sensitive Groups 16 of 179 days1997: Unhealthy 2 of 179 days1998: Good 113 of 178 days1998: Moderate 47 of 178 days1998: Unhealthy for Sensitive Groups 15 of 178 days1998: Unhealthy 3 of 178 days1999: Good 112 of 180 days1999: Moderate 44 of 180 days1999: Unhealthy for Sensitive Groups 18 of 180 days1999: Unhealthy 5 of 180 days1999: Very Unhealthy 1 of 180 days2000: Good 134 of 184 days2000: Moderate 41 of 184 days2000: Unhealthy for Sensitive Groups 9 of 184 days20002001: Good 116 of 184 days2001: Moderate 50 of 184 days2001: Unhealthy for Sensitive Groups 14 of 184 days2001: Unhealthy 4 of 184 days2002: Good 104 of 177 days2002: Moderate 47 of 177 days2002: Unhealthy for Sensitive Groups 25 of 177 days2002: Unhealthy 1 of 177 days2003: Good 109 of 183 days2003: Moderate 53 of 183 days2003: Unhealthy for Sensitive Groups 20 of 183 days2003: Unhealthy 1 of 183 days2004: Good 146 of 184 days2004: Moderate 37 of 184 days2004: Unhealthy for Sensitive Groups 1 of 184 days2005: Good 114 of 186 days2005: Moderate 50 of 186 days2005: Unhealthy for Sensitive Groups 20 of 186 days2005: Unhealthy 2 of 186 days20052006: Good 134 of 186 days2006: Moderate 46 of 186 days2006: Unhealthy for Sensitive Groups 6 of 186 days2007: Good 131 of 189 days2007: Moderate 49 of 189 days2007: Unhealthy for Sensitive Groups 8 of 189 days2007: Unhealthy 1 of 189 days2008: Good 152 of 191 days2008: Moderate 37 of 191 days2008: Unhealthy for Sensitive Groups 2 of 191 days2009: Good 160 of 201 days2009: Moderate 39 of 201 days2009: Unhealthy for Sensitive Groups 2 of 201 days2010: Good 165 of 196 days2010: Moderate 31 of 196 days20102011: Good 151 of 185 days2011: Moderate 32 of 185 days2011: Unhealthy for Sensitive Groups 2 of 185 days2012: Good 127 of 191 days2012: Moderate 49 of 191 days2012: Unhealthy for Sensitive Groups 14 of 191 days2012: Unhealthy 1 of 191 days2013: Good 166 of 195 days2013: Moderate 28 of 195 days2013: Unhealthy for Sensitive Groups 1 of 195 days2014: Good 159 of 193 days2014: Moderate 30 of 193 days2014: Unhealthy for Sensitive Groups 4 of 193 days2015: Good 170 of 199 days2015: Moderate 28 of 199 days2015: Unhealthy for Sensitive Groups 1 of 199 days20152016: Good 161 of 188 days2016: Moderate 22 of 188 days2016: Unhealthy for Sensitive Groups 5 of 188 days2017: Good 219 of 243 days2017: Moderate 24 of 243 days2018: Good 202 of 237 days2018: Moderate 33 of 237 days2018: Unhealthy for Sensitive Groups 2 of 237 days2019: Good 189 of 205 days2019: Moderate 15 of 205 days2019: Unhealthy for Sensitive Groups 1 of 205 days2020: Good 180 of 198 days2020: Moderate 14 of 198 days2020: Unhealthy for Sensitive Groups 4 of 198 days20202021: Good 184 of 221 days2021: Moderate 36 of 221 days2021: Unhealthy for Sensitive Groups 1 of 221 days2022: Good 181 of 200 days2022: Moderate 16 of 200 days2022: Unhealthy for Sensitive Groups 3 of 200 days2023: Good 138 of 203 days2023: Moderate 48 of 203 days2023: Unhealthy for Sensitive Groups 17 of 203 days2024: Good 169 of 206 days2024: Moderate 37 of 206 days2025: Good 158 of 199 days2025: Moderate 38 of 199 days2025: Unhealthy for Sensitive Groups 3 of 199 days2025
  • 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 and 90th-percentile daily AQI, by year0501001501980: 90th percentile AQI 1081981: 90th percentile AQI 1001987: 90th percentile AQI 901988: 90th percentile AQI 1431989: 90th percentile AQI 1001990: 90th percentile AQI 771991: 90th percentile AQI 1191992: 90th percentile AQI 711993: 90th percentile AQI 671994: 90th percentile AQI 841995: 90th percentile AQI 1051996: 90th percentile AQI 901997: 90th percentile AQI 1011998: 90th percentile AQI 1051999: 90th percentile AQI 1082000: 90th percentile AQI 872001: 90th percentile AQI 1002002: 90th percentile AQI 1122003: 90th percentile AQI 1012004: 90th percentile AQI 742005: 90th percentile AQI 1052006: 90th percentile AQI 742007: 90th percentile AQI 842008: 90th percentile AQI 612009: 90th percentile AQI 642010: 90th percentile AQI 642011: 90th percentile AQI 772012: 90th percentile AQI 902013: 90th percentile AQI 612014: 90th percentile AQI 612015: 90th percentile AQI 582016: 90th percentile AQI 612017: 90th percentile AQI 502018: 90th percentile AQI 582019: 90th percentile AQI 492020: 90th percentile AQI 502021: 90th percentile AQI 612022: 90th percentile AQI 502023: 90th percentile AQI 932024: 90th percentile AQI 612025: 90th percentile AQI 671980: Median AQI 431981: Median AQI 381987: Median AQI 311988: Median AQI 431989: Median AQI 421990: Median AQI 381991: Median AQI 431992: Median AQI 361993: Median AQI 391994: Median AQI 441995: Median AQI 441996: Median AQI 441997: Median AQI 441998: Median AQI 471999: Median AQI 462000: Median AQI 442001: Median AQI 462002: Median AQI 462003: Median AQI 462004: Median AQI 402005: Median AQI 462006: Median AQI 442007: Median AQI 442008: Median AQI 422009: Median AQI 392010: Median AQI 412011: Median AQI 412012: Median AQI 442013: Median AQI 392014: Median AQI 402015: Median AQI 402016: Median AQI 382017: Median AQI 392018: Median AQI 402019: Median AQI 372020: Median AQI 392021: Median AQI 412022: Median AQI 392023: Median AQI 442024: Median AQI 422025: Median AQI 42198019901995200020052010201520202025
  • 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.

PollutantDays as main pollutantShare of monitored days
Ozone199100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20251991583830004267112Ozone
20242061693700004261100Ozone
202320313848170004493143Ozone
20222001811630003950105Ozone
20212211843610004161101Ozone
20201981801440003950136Ozone
20192051891510003749112Ozone
20182372023320004058126Ozone
2017243219240000395090Ozone
20161881612250003861115Ozone
20151991702810004058108Ozone
20141931593040004061140Ozone
20131951662810003961115Ozone
201219112749141004490174Ozone
20111851513220004177112Ozone
20101961653100004164100Ozone
20092011603920003964119Ozone
20081911523720004261105Ozone
20071891314981004484154Ozone
20061861344660004474129Ozone
2005186114502020046105161Ozone
20041841463710004074129Ozone
2003183109532010046101151Ozone
2002177104472510046112182Ozone
2001184116501440046100190Ozone
20001841344190004487143Ozone
1999180112441851046108205Ozone
1998178113471530047105164Ozone
1997179128331620044101166Ozone
199617512934102004490169Ozone
1995175115381840044105177Ozone
19941821274582004484166Ozone
19932251843380003967147Ozone
199227022828104003671172Ozone
19912701814432121043119201Ozone
19902642094861003877179Ozone
1989273187592241042100203Ozone
19882751714539182043143214Ozone
19871391121890003190147Ozone
1981196143351620038100166Ozone
198014697311260043108182Ozone

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 Wisconsin with a similar median AQI in 2025

All monitored counties in Wisconsin

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