EnviroNearby

Washington County, Ohio air quality history

Daily Air Quality Index summaries from EPA monitors in Washington, Ohio, 1990–2025.

88%
Good days in 2025
40
Median daily AQI, 2025
2
Days above 100 in 2025
242
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Washington, Ohio on 242 days. 214 of those days (88%) were in the Good range, and the median daily AQI was 40. That median is lower than the typical monitored county in Ohio (median 43 across 36 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 242 days. Across the years with fuller monitoring, the share of Good days rose: an average of 59% in 1991–1993 versus 87% in 2023–2025.

EPA did not report an AQI for every day of 2025 here (242 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.

Years with fewer than 120 monitored days (1990) 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.

Share of monitored days in each AQI category, by year0%25%50%75%100%1990: Good 68 of 106 days1990: Moderate 21 of 106 days1990: Unhealthy for Sensitive Groups 14 of 106 days1990: Unhealthy 3 of 106 days19901991: Good 112 of 210 days1991: Moderate 54 of 210 days1991: Unhealthy for Sensitive Groups 26 of 210 days1991: Unhealthy 16 of 210 days1991: Very Unhealthy 2 of 210 days1992: Good 141 of 207 days1992: Moderate 50 of 207 days1992: Unhealthy for Sensitive Groups 12 of 207 days1992: Unhealthy 2 of 207 days1992: Very Unhealthy 2 of 207 days1993: Good 106 of 194 days1993: Moderate 43 of 194 days1993: Unhealthy for Sensitive Groups 27 of 194 days1993: Unhealthy 16 of 194 days1993: Very Unhealthy 2 of 194 days1994: Good 110 of 211 days1994: Moderate 62 of 211 days1994: Unhealthy for Sensitive Groups 24 of 211 days1994: Unhealthy 15 of 211 days1995: Good 111 of 206 days1995: Moderate 67 of 206 days1995: Unhealthy for Sensitive Groups 18 of 206 days1995: Unhealthy 10 of 206 days19951996: Good 165 of 244 days1996: Moderate 59 of 244 days1996: Unhealthy for Sensitive Groups 16 of 244 days1996: Unhealthy 4 of 244 days1997: Good 227 of 287 days1997: Moderate 47 of 287 days1997: Unhealthy for Sensitive Groups 10 of 287 days1997: Unhealthy 3 of 287 days1998: Good 180 of 289 days1998: Moderate 71 of 289 days1998: Unhealthy for Sensitive Groups 27 of 289 days1998: Unhealthy 11 of 289 days1999: Good 179 of 281 days1999: Moderate 59 of 281 days1999: Unhealthy for Sensitive Groups 35 of 281 days1999: Unhealthy 7 of 281 days1999: Very Unhealthy 1 of 281 days2000: Good 201 of 285 days2000: Moderate 66 of 285 days2000: Unhealthy for Sensitive Groups 15 of 285 days2000: Unhealthy 3 of 285 days20002001: Good 187 of 287 days2001: Moderate 75 of 287 days2001: Unhealthy for Sensitive Groups 22 of 287 days2001: Unhealthy 3 of 287 days2002: Good 185 of 283 days2002: Moderate 57 of 283 days2002: Unhealthy for Sensitive Groups 26 of 283 days2002: Unhealthy 14 of 283 days2002: Very Unhealthy 1 of 283 days2003: Good 173 of 247 days2003: Moderate 63 of 247 days2003: Unhealthy for Sensitive Groups 8 of 247 days2003: Unhealthy 1 of 247 days2003: Very Unhealthy 2 of 247 days2004: Good 177 of 237 days2004: Moderate 52 of 237 days2004: Unhealthy for Sensitive Groups 8 of 237 days2005: Good 140 of 234 days2005: Moderate 64 of 234 days2005: Unhealthy for Sensitive Groups 24 of 234 days2005: Unhealthy 6 of 234 days20052006: Good 162 of 237 days2006: Moderate 62 of 237 days2006: Unhealthy for Sensitive Groups 11 of 237 days2006: Unhealthy 2 of 237 days2007: Good 128 of 229 days2007: Moderate 76 of 229 days2007: Unhealthy for Sensitive Groups 21 of 229 days2007: Unhealthy 4 of 229 days2008: Good 145 of 214 days2008: Moderate 59 of 214 days2008: Unhealthy for Sensitive Groups 9 of 214 days2008: Unhealthy 1 of 214 days2009: Good 172 of 214 days2009: Moderate 42 of 214 days2010: Good 130 of 214 days2010: Moderate 74 of 214 days2010: Unhealthy for Sensitive Groups 10 of 214 days20102011: Good 158 of 211 days2011: Moderate 49 of 211 days2011: Unhealthy for Sensitive Groups 4 of 211 days2012: Good 134 of 214 days2012: Moderate 73 of 214 days2012: Unhealthy for Sensitive Groups 7 of 214 days2013: Good 192 of 213 days2013: Moderate 20 of 213 days2013: Unhealthy for Sensitive Groups 1 of 213 days2014: Good 169 of 200 days2014: Moderate 29 of 200 days2014: Unhealthy for Sensitive Groups 2 of 200 days2015: Good 181 of 214 days2015: Moderate 32 of 214 days2015: Unhealthy for Sensitive Groups 1 of 214 days20152016: Good 189 of 214 days2016: Moderate 25 of 214 days2017: Good 219 of 245 days2017: Moderate 26 of 245 days2018: Good 216 of 245 days2018: Moderate 26 of 245 days2018: Unhealthy for Sensitive Groups 3 of 245 days2019: Good 219 of 245 days2019: Moderate 26 of 245 days2020: Good 233 of 245 days2020: Moderate 11 of 245 days2020: Unhealthy for Sensitive Groups 1 of 245 days20202021: Good 222 of 245 days2021: Moderate 23 of 245 days2022: Good 222 of 245 days2022: Moderate 23 of 245 days2023: Good 206 of 238 days2023: Moderate 32 of 238 days2024: Good 212 of 244 days2024: Moderate 32 of 244 days2025: Good 214 of 242 days2025: Moderate 26 of 242 days2025: Unhealthy for Sensitive Groups 2 of 242 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 year0501001501990: 90th percentile AQI 1121991: 90th percentile AQI 1501992: 90th percentile AQI 1001993: 90th percentile AQI 1471994: 90th percentile AQI 1261995: 90th percentile AQI 1191996: 90th percentile AQI 1001997: 90th percentile AQI 771998: 90th percentile AQI 1191999: 90th percentile AQI 1152000: 90th percentile AQI 872001: 90th percentile AQI 1002002: 90th percentile AQI 1192003: 90th percentile AQI 842004: 90th percentile AQI 802005: 90th percentile AQI 1082006: 90th percentile AQI 842007: 90th percentile AQI 1052008: 90th percentile AQI 802009: 90th percentile AQI 612010: 90th percentile AQI 902011: 90th percentile AQI 742012: 90th percentile AQI 902013: 90th percentile AQI 502014: 90th percentile AQI 582015: 90th percentile AQI 612016: 90th percentile AQI 542017: 90th percentile AQI 512018: 90th percentile AQI 542019: 90th percentile AQI 512020: 90th percentile AQI 482021: 90th percentile AQI 502022: 90th percentile AQI 502023: 90th percentile AQI 542024: 90th percentile AQI 542025: 90th percentile AQI 541990: Median AQI 421991: Median AQI 491992: Median AQI 441993: Median AQI 471994: Median AQI 501995: Median AQI 491996: Median AQI 421997: Median AQI 381998: Median AQI 441999: Median AQI 452000: Median AQI 422001: Median AQI 442002: Median AQI 442003: Median AQI 432004: Median AQI 432005: Median AQI 482006: Median AQI 442007: Median AQI 492008: Median AQI 452009: Median AQI 412010: Median AQI 462011: Median AQI 422012: Median AQI 472013: Median AQI 412014: Median AQI 422015: Median AQI 402016: Median AQI 402017: Median AQI 412018: Median AQI 392019: Median AQI 412020: Median AQI 382021: Median AQI 392022: Median AQI 392023: Median AQI 422024: Median AQI 412025: Median AQI 4019901995200020052010201520202025
  • 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
Ozone242100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20252422142620004054105Ozone
2024244212320000415490Ozone
20232382063200004254100Ozone
2022245222230000395084Ozone
2021245222230000395087Ozone
20202452331110003848108Ozone
2019245219260000415187Ozone
20182452162630003954105Ozone
2017245219260000415197Ozone
2016214189250000405490Ozone
20152141813210004061115Ozone
20142001692920004258112Ozone
20132131922010004150112Ozone
20122141347370004790150Ozone
20112111584940004274143Ozone
201021413074100004690129Ozone
20092141724200004161100Ozone
20082141455991004580174Ozone
2007229128762140049105164Ozone
200623716262112004484166Ozone
2005234140642460048108179Ozone
20042371775280004380129Ozone
20032471736381204384222Ozone
20022831855726141044119201Ozone
2001287187752230044100174Ozone
200028520166153004287179Ozone
1999281179593571045115214Ozone
19982891807127110044119200Ozone
199728722747103003877177Ozone
1996244165591640042100187Ozone
19952061116718100049119185Ozone
19942111106224150050126200Ozone
19931941064327162047147202Ozone
1992207141501222044100210Ozone
19912101125426162049150213Ozone
199010668211430042112172Ozone

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 Ohio with a similar median AQI in 2025

All monitored counties in Ohio

Source: U.S. EPA AirData, “Annual AQI by County” files for 1990–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem