EnviroNearby

Hamilton County, Indiana air quality history

Daily Air Quality Index summaries from EPA monitors in Hamilton, Indiana, 1985–2025.

64%
Good days in 2025
44
Median daily AQI, 2025
5
Days above 100 in 2025
364
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Hamilton, Indiana on 364 days. 233 of those days (64%) were in the Good range, and the median daily AQI was 44. That median is higher than the typical monitored county in Indiana (median 41 across 33 counties), and higher than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 201 days. Across the years with fuller monitoring, the share of Good days rose: an average of 51% in 1985–1988 versus 64% in 2023–2025.

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%1985: Good 60 of 123 days1985: Moderate 46 of 123 days1985: Unhealthy for Sensitive Groups 13 of 123 days1985: Unhealthy 4 of 123 days19851987: Good 110 of 207 days1987: Moderate 53 of 207 days1987: Unhealthy for Sensitive Groups 34 of 207 days1987: Unhealthy 10 of 207 days1988: Good 105 of 207 days1988: Moderate 50 of 207 days1988: Unhealthy for Sensitive Groups 25 of 207 days1988: Unhealthy 25 of 207 days1988: Very Unhealthy 2 of 207 days1989: Good 117 of 207 days1989: Moderate 55 of 207 days1989: Unhealthy for Sensitive Groups 26 of 207 days1989: Unhealthy 9 of 207 days1990: Good 148 of 209 days1990: Moderate 39 of 209 days1990: Unhealthy for Sensitive Groups 17 of 209 days1990: Unhealthy 5 of 209 days1991: Good 109 of 179 days1991: Moderate 49 of 179 days1991: Unhealthy for Sensitive Groups 18 of 179 days1991: Unhealthy 3 of 179 days19911992: Good 115 of 176 days1992: Moderate 48 of 176 days1992: Unhealthy for Sensitive Groups 11 of 176 days1992: Unhealthy 2 of 176 days1993: Good 94 of 174 days1993: Moderate 52 of 174 days1993: Unhealthy for Sensitive Groups 23 of 174 days1993: Unhealthy 5 of 174 days1994: Good 83 of 181 days1994: Moderate 48 of 181 days1994: Unhealthy for Sensitive Groups 38 of 181 days1994: Unhealthy 12 of 181 days1995: Good 86 of 183 days1995: Moderate 56 of 183 days1995: Unhealthy for Sensitive Groups 29 of 183 days1995: Unhealthy 11 of 183 days1995: Very Unhealthy 1 of 183 days1996: Good 97 of 181 days1996: Moderate 49 of 181 days1996: Unhealthy for Sensitive Groups 25 of 181 days1996: Unhealthy 9 of 181 days1996: Very Unhealthy 1 of 181 days19961997: Good 113 of 181 days1997: Moderate 38 of 181 days1997: Unhealthy for Sensitive Groups 22 of 181 days1997: Unhealthy 7 of 181 days1997: Very Unhealthy 1 of 181 days1998: Good 60 of 183 days1998: Moderate 83 of 183 days1998: Unhealthy for Sensitive Groups 25 of 183 days1998: Unhealthy 14 of 183 days1998: Very Unhealthy 1 of 183 days1999: Good 76 of 181 days1999: Moderate 58 of 181 days1999: Unhealthy for Sensitive Groups 30 of 181 days1999: Unhealthy 17 of 181 days2000: Good 114 of 183 days2000: Moderate 55 of 183 days2000: Unhealthy for Sensitive Groups 10 of 183 days2000: Unhealthy 4 of 183 days2001: Good 99 of 183 days2001: Moderate 52 of 183 days2001: Unhealthy for Sensitive Groups 28 of 183 days2001: Unhealthy 4 of 183 days20012002: Good 97 of 183 days2002: Moderate 51 of 183 days2002: Unhealthy for Sensitive Groups 19 of 183 days2002: Unhealthy 14 of 183 days2002: Very Unhealthy 2 of 183 days2003: Good 99 of 183 days2003: Moderate 64 of 183 days2003: Unhealthy for Sensitive Groups 15 of 183 days2003: Unhealthy 4 of 183 days2003: Very Unhealthy 1 of 183 days2004: Good 114 of 182 days2004: Moderate 55 of 182 days2004: Unhealthy for Sensitive Groups 13 of 182 days2005: Good 96 of 183 days2005: Moderate 58 of 183 days2005: Unhealthy for Sensitive Groups 25 of 183 days2005: Unhealthy 4 of 183 days2006: Good 110 of 183 days2006: Moderate 61 of 183 days2006: Unhealthy for Sensitive Groups 12 of 183 days20062007: Good 74 of 165 days2007: Moderate 63 of 165 days2007: Unhealthy for Sensitive Groups 25 of 165 days2007: Unhealthy 3 of 165 days2008: Good 113 of 182 days2008: Moderate 61 of 182 days2008: Unhealthy for Sensitive Groups 7 of 182 days2008: Unhealthy 1 of 182 days2009: Good 129 of 183 days2009: Moderate 50 of 183 days2009: Unhealthy for Sensitive Groups 4 of 183 days2010: Good 119 of 180 days2010: Moderate 53 of 180 days2010: Unhealthy for Sensitive Groups 8 of 180 days2011: Good 127 of 173 days2011: Moderate 41 of 173 days2011: Unhealthy for Sensitive Groups 5 of 173 days20112012: Good 114 of 183 days2012: Moderate 56 of 183 days2012: Unhealthy for Sensitive Groups 13 of 183 days2013: Good 166 of 182 days2013: Moderate 16 of 182 days2014: Good 191 of 358 days2014: Moderate 165 of 358 days2014: Unhealthy for Sensitive Groups 2 of 358 days2015: Good 213 of 360 days2015: Moderate 147 of 360 days2016: Good 189 of 359 days2016: Moderate 167 of 359 days2016: Unhealthy for Sensitive Groups 3 of 359 days20162017: Good 229 of 365 days2017: Moderate 134 of 365 days2017: Unhealthy for Sensitive Groups 2 of 365 days2018: Good 229 of 365 days2018: Moderate 130 of 365 days2018: Unhealthy for Sensitive Groups 6 of 365 days2019: Good 214 of 365 days2019: Moderate 149 of 365 days2019: Unhealthy for Sensitive Groups 2 of 365 days2020: Good 247 of 366 days2020: Moderate 119 of 366 days2021: Good 232 of 365 days2021: Moderate 133 of 365 days20212022: Good 241 of 365 days2022: Moderate 124 of 365 days2023: Good 220 of 364 days2023: Moderate 134 of 364 days2023: Unhealthy for Sensitive Groups 8 of 364 days2023: Unhealthy 2 of 364 days2024: Good 244 of 366 days2024: Moderate 121 of 366 days2024: Unhealthy for Sensitive Groups 1 of 366 days2025: Good 233 of 364 days2025: Moderate 126 of 364 days2025: Unhealthy for Sensitive Groups 5 of 364 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 year0501001502001985: 90th percentile AQI 1121987: 90th percentile AQI 1291988: 90th percentile AQI 1591989: 90th percentile AQI 1221990: 90th percentile AQI 1011991: 90th percentile AQI 1051992: 90th percentile AQI 901993: 90th percentile AQI 1191994: 90th percentile AQI 1401995: 90th percentile AQI 1331996: 90th percentile AQI 1261997: 90th percentile AQI 1151998: 90th percentile AQI 1401999: 90th percentile AQI 1472000: 90th percentile AQI 972001: 90th percentile AQI 1152002: 90th percentile AQI 1472003: 90th percentile AQI 1052004: 90th percentile AQI 932005: 90th percentile AQI 1152006: 90th percentile AQI 972007: 90th percentile AQI 1152008: 90th percentile AQI 932009: 90th percentile AQI 772010: 90th percentile AQI 872011: 90th percentile AQI 802012: 90th percentile AQI 972013: 90th percentile AQI 502014: 90th percentile AQI 662015: 90th percentile AQI 642016: 90th percentile AQI 652017: 90th percentile AQI 602018: 90th percentile AQI 632019: 90th percentile AQI 642020: 90th percentile AQI 592021: 90th percentile AQI 662022: 90th percentile AQI 632023: 90th percentile AQI 692024: 90th percentile AQI 612025: 90th percentile AQI 621985: Median AQI 511987: Median AQI 491988: Median AQI 501989: Median AQI 481990: Median AQI 411991: Median AQI 461992: Median AQI 441993: Median AQI 491994: Median AQI 581995: Median AQI 511996: Median AQI 491997: Median AQI 461998: Median AQI 641999: Median AQI 612000: Median AQI 482001: Median AQI 492002: Median AQI 492003: Median AQI 502004: Median AQI 462005: Median AQI 492006: Median AQI 472007: Median AQI 542008: Median AQI 472009: Median AQI 442010: Median AQI 442011: Median AQI 442012: Median AQI 482013: Median AQI 392014: Median AQI 482015: Median AQI 442016: Median AQI 492017: Median AQI 462018: Median AQI 452019: Median AQI 472020: Median AQI 442021: Median AQI 442022: Median AQI 432023: Median AQI 462024: Median AQI 442025: Median AQI 44198519911996200120062011201620212025
  • 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
Fine particles (PM2.5)20155%
Ozone16345%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536423312650004462118PM2.5
202436624412110004461108PM2.5
202336422013482004669190PM2.5
202236524112400004363100PM2.5
202136523213300004466100PM2.5
20203662471190000445997PM2.5
201936521414920004764119PM2.5
201836522913060004563129PM2.5
201736522913420004660105PM2.5
201635918916730004965115PM2.5
20153602131470000446493PM2.5
201435819116520004866129PM2.5
2013182166160000395084Ozone
201218311456130004897126Ozone
20111731274150004480150Ozone
20101801195380004487122Ozone
20091831295040004477115Ozone
20081821136171004793154Ozone
200716574632530054115156Ozone
200618311061120004797150Ozone
200518396582540049115182Ozone
200418211455130004693129Ozone
200318399641541050105203Ozone
2002183975119142049147203Ozone
200118399522840049115195Ozone
200018311455104004897187Ozone
1999181765830170061147195Ozone
1998183608325141064140207Ozone
1997181113382271046115218Ozone
199618197492591049126205Ozone
1995183865629111051133206Ozone
1994181834838120058140197Ozone
199317494522350049119192Ozone
199217611548112004490190Ozone
1991179109491830046105166Ozone
1990209148391750041101182Ozone
1989207117552690048122195Ozone
19882071055025252050159203Ozone
19872071105334100049129192Ozone
198512360461340051112190Ozone

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 1985–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem