EnviroNearby

Knox County, Ohio air quality history

Daily Air Quality Index summaries from EPA monitors in Knox, Ohio, 1988–2025.

85%
Good days in 2025
39
Median daily AQI, 2025
2
Days above 100 in 2025
245
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Knox, Ohio on 245 days. 209 of those days (85%) were in the Good range, and the median daily AQI was 39. 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 245 days. Across the years with fuller monitoring, the share of Good days rose: an average of 70% in 1989–1991 versus 84% in 2023–2025.

EPA did not report an AQI for every day of 2025 here (245 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 (1988) 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%1988: Good 70 of 92 days1988: Moderate 12 of 92 days1988: Unhealthy for Sensitive Groups 7 of 92 days1988: Unhealthy 3 of 92 days19881989: Good 133 of 208 days1989: Moderate 59 of 208 days1989: Unhealthy for Sensitive Groups 14 of 208 days1989: Unhealthy 2 of 208 days1990: Good 158 of 212 days1990: Moderate 40 of 212 days1990: Unhealthy for Sensitive Groups 11 of 212 days1990: Unhealthy 3 of 212 days1991: Good 152 of 213 days1991: Moderate 43 of 213 days1991: Unhealthy for Sensitive Groups 12 of 213 days1991: Unhealthy 6 of 213 days1992: Good 139 of 205 days1992: Moderate 52 of 205 days1992: Unhealthy for Sensitive Groups 11 of 205 days1992: Unhealthy 3 of 205 days1993: Good 133 of 212 days1993: Moderate 49 of 212 days1993: Unhealthy for Sensitive Groups 25 of 212 days1993: Unhealthy 5 of 212 days19931994: Good 126 of 210 days1994: Moderate 51 of 210 days1994: Unhealthy for Sensitive Groups 28 of 210 days1994: Unhealthy 5 of 210 days1995: Good 130 of 206 days1995: Moderate 56 of 206 days1995: Unhealthy for Sensitive Groups 15 of 206 days1995: Unhealthy 5 of 206 days1996: Good 136 of 212 days1996: Moderate 45 of 212 days1996: Unhealthy for Sensitive Groups 23 of 212 days1996: Unhealthy 8 of 212 days1997: Good 150 of 213 days1997: Moderate 42 of 213 days1997: Unhealthy for Sensitive Groups 17 of 213 days1997: Unhealthy 4 of 213 days1998: Good 130 of 213 days1998: Moderate 55 of 213 days1998: Unhealthy for Sensitive Groups 20 of 213 days1998: Unhealthy 8 of 213 days19981999: Good 124 of 214 days1999: Moderate 60 of 214 days1999: Unhealthy for Sensitive Groups 23 of 214 days1999: Unhealthy 6 of 214 days1999: Very Unhealthy 1 of 214 days2000: Good 138 of 214 days2000: Moderate 60 of 214 days2000: Unhealthy for Sensitive Groups 10 of 214 days2000: Unhealthy 5 of 214 days2000: Very Unhealthy 1 of 214 days2001: Good 128 of 214 days2001: Moderate 56 of 214 days2001: Unhealthy for Sensitive Groups 23 of 214 days2001: Unhealthy 7 of 214 days2002: Good 121 of 209 days2002: Moderate 48 of 209 days2002: Unhealthy for Sensitive Groups 26 of 209 days2002: Unhealthy 14 of 209 days2003: Good 151 of 214 days2003: Moderate 48 of 214 days2003: Unhealthy for Sensitive Groups 12 of 214 days2003: Unhealthy 2 of 214 days2003: Very Unhealthy 1 of 214 days20032004: Good 163 of 208 days2004: Moderate 36 of 208 days2004: Unhealthy for Sensitive Groups 9 of 208 days2005: Good 128 of 213 days2005: Moderate 66 of 213 days2005: Unhealthy for Sensitive Groups 17 of 213 days2005: Unhealthy 2 of 213 days2006: Good 152 of 213 days2006: Moderate 51 of 213 days2006: Unhealthy for Sensitive Groups 10 of 213 days2007: Good 135 of 214 days2007: Moderate 65 of 214 days2007: Unhealthy for Sensitive Groups 13 of 214 days2007: Unhealthy 1 of 214 days2008: Good 154 of 214 days2008: Moderate 53 of 214 days2008: Unhealthy for Sensitive Groups 7 of 214 days20082009: Good 184 of 212 days2009: Moderate 28 of 212 days2010: Good 154 of 214 days2010: Moderate 56 of 214 days2010: Unhealthy for Sensitive Groups 4 of 214 days2011: Good 166 of 214 days2011: Moderate 41 of 214 days2011: Unhealthy for Sensitive Groups 7 of 214 days2012: Good 135 of 214 days2012: Moderate 71 of 214 days2012: Unhealthy for Sensitive Groups 7 of 214 days2012: Unhealthy 1 of 214 days2013: Good 182 of 214 days2013: Moderate 30 of 214 days2013: Unhealthy for Sensitive Groups 2 of 214 days20132014: Good 179 of 214 days2014: Moderate 35 of 214 days2015: Good 178 of 210 days2015: Moderate 28 of 210 days2015: Unhealthy for Sensitive Groups 4 of 210 days2016: Good 175 of 213 days2016: Moderate 38 of 213 days2017: Good 223 of 245 days2017: Moderate 22 of 245 days2018: Good 208 of 245 days2018: Moderate 36 of 245 days2018: Unhealthy for Sensitive Groups 1 of 245 days20182019: Good 218 of 245 days2019: Moderate 27 of 245 days2020: Good 226 of 245 days2020: Moderate 19 of 245 days2021: Good 225 of 245 days2021: Moderate 20 of 245 days2022: Good 225 of 245 days2022: Moderate 19 of 245 days2022: Unhealthy for Sensitive Groups 1 of 245 days2023: Good 200 of 245 days2023: Moderate 44 of 245 days2023: Unhealthy for Sensitive Groups 1 of 245 days20232024: Good 208 of 245 days2024: Moderate 36 of 245 days2024: Unhealthy for Sensitive Groups 1 of 245 days2025: Good 209 of 245 days2025: Moderate 34 of 245 days2025: Unhealthy for Sensitive Groups 1 of 245 days2025: Unhealthy 1 of 245 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 year0501001501988: 90th percentile AQI 1081989: 90th percentile AQI 971990: 90th percentile AQI 871991: 90th percentile AQI 1001992: 90th percentile AQI 971993: 90th percentile AQI 1151994: 90th percentile AQI 1081995: 90th percentile AQI 1001996: 90th percentile AQI 1121997: 90th percentile AQI 1001998: 90th percentile AQI 1081999: 90th percentile AQI 1192000: 90th percentile AQI 932001: 90th percentile AQI 1122002: 90th percentile AQI 1402003: 90th percentile AQI 872004: 90th percentile AQI 842005: 90th percentile AQI 1002006: 90th percentile AQI 802007: 90th percentile AQI 902008: 90th percentile AQI 802009: 90th percentile AQI 542010: 90th percentile AQI 742011: 90th percentile AQI 672012: 90th percentile AQI 872013: 90th percentile AQI 582014: 90th percentile AQI 582015: 90th percentile AQI 612016: 90th percentile AQI 642017: 90th percentile AQI 502018: 90th percentile AQI 642019: 90th percentile AQI 512020: 90th percentile AQI 492021: 90th percentile AQI 492022: 90th percentile AQI 502023: 90th percentile AQI 612024: 90th percentile AQI 542025: 90th percentile AQI 541988: Median AQI 331989: Median AQI 451990: Median AQI 401991: Median AQI 421992: Median AQI 411993: Median AQI 461994: Median AQI 461995: Median AQI 461996: Median AQI 451997: Median AQI 431998: Median AQI 471999: Median AQI 472000: Median AQI 452001: Median AQI 482002: Median AQI 492003: Median AQI 442004: Median AQI 432005: Median AQI 462006: Median AQI 432007: Median AQI 452008: Median AQI 442009: Median AQI 392010: Median AQI 422011: Median AQI 422012: Median AQI 452013: Median AQI 402014: Median AQI 412015: Median AQI 402016: Median AQI 412017: Median AQI 382018: Median AQI 402019: Median AQI 412020: Median AQI 382021: Median AQI 382022: Median AQI 392023: Median AQI 422024: Median AQI 412025: Median AQI 39198819931998200320082013201820232025
  • 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
Ozone245100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20252452093411003954159Ozone
20242452083610004154101Ozone
20232452004410004261105Ozone
20222452251910003950119Ozone
2021245225200000384997Ozone
2020245226190000384980Ozone
2019245218270000415193Ozone
20182452083610004064115Ozone
20172452232200003850100Ozone
20162131753800004164100Ozone
20152101782840004061119Ozone
2014214179350000415897Ozone
20132141823020004058108Ozone
20122141357171004587182Ozone
20112141664170004267147Ozone
20102141545640004274122Ozone
20092121842800003954100Ozone
20082141545370004480122Ozone
200721413565131004590156Ozone
200621315251100004380150Ozone
2005213128661720046100190Ozone
20042081633690004384143Ozone
200321415148122104487207Ozone
20022091214826140049140185Ozone
2001214128562370048112179Ozone
200021413860105104593207Ozone
1999214124602361047119202Ozone
1998213130552080047108190Ozone
1997213150421740043100200Ozone
1996212136452380045112197Ozone
1995206130561550046100197Ozone
1994210126512850046108174Ozone
1993212133492550046115190Ozone
199220513952113004197197Ozone
1991213152431260042100174Ozone
199021215840113004087166Ozone
198920813359142004597159Ozone
1988927012730033108169Ozone

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 1988–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem