EnviroNearby

Washtenaw County, Michigan air quality history

Daily Air Quality Index summaries from EPA monitors in Washtenaw, Michigan, 1980–2025.

69%
Good days in 2025
41
Median daily AQI, 2025
8
Days above 100 in 2025
365
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Washtenaw, Michigan on 365 days. 253 of those days (69%) were in the Good range, and the median daily AQI was 41. That median is about the same as the typical monitored county in Michigan (median 39 across 26 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 229 days. Across the years with fuller monitoring, the share of Good days fell: an average of 79% in 1980–1982 versus 61% 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%1980: Good 183 of 226 days1980: Moderate 28 of 226 days1980: Unhealthy for Sensitive Groups 11 of 226 days1980: Unhealthy 4 of 226 days19801981: Good 222 of 241 days1981: Moderate 14 of 241 days1981: Unhealthy for Sensitive Groups 4 of 241 days1981: Unhealthy 1 of 241 days1982: Good 119 of 184 days1982: Moderate 45 of 184 days1982: Unhealthy for Sensitive Groups 19 of 184 days1982: Unhealthy 1 of 184 days1983: Good 149 of 205 days1983: Moderate 39 of 205 days1983: Unhealthy for Sensitive Groups 16 of 205 days1983: Unhealthy 1 of 205 days1984: Good 123 of 159 days1984: Moderate 30 of 159 days1984: Unhealthy for Sensitive Groups 6 of 159 days1985: Good 121 of 166 days1985: Moderate 37 of 166 days1985: Unhealthy for Sensitive Groups 7 of 166 days1985: Unhealthy 1 of 166 days19851986: Good 161 of 198 days1986: Moderate 31 of 198 days1986: Unhealthy for Sensitive Groups 6 of 198 days1987: Good 148 of 213 days1987: Moderate 37 of 213 days1987: Unhealthy for Sensitive Groups 24 of 213 days1987: Unhealthy 3 of 213 days1987: Very Unhealthy 1 of 213 days1988: Good 122 of 214 days1988: Moderate 48 of 214 days1988: Unhealthy for Sensitive Groups 18 of 214 days1988: Unhealthy 22 of 214 days1988: Very Unhealthy 4 of 214 days1989: Good 143 of 213 days1989: Moderate 47 of 213 days1989: Unhealthy for Sensitive Groups 20 of 213 days1989: Unhealthy 3 of 213 days1990: Good 287 of 364 days1990: Moderate 51 of 364 days1990: Unhealthy for Sensitive Groups 19 of 364 days1990: Unhealthy 7 of 364 days19901991: Good 273 of 360 days1991: Moderate 52 of 360 days1991: Unhealthy for Sensitive Groups 25 of 360 days1991: Unhealthy 10 of 360 days1992: Good 304 of 364 days1992: Moderate 43 of 364 days1992: Unhealthy for Sensitive Groups 11 of 364 days1992: Unhealthy 6 of 364 days1993: Good 312 of 364 days1993: Moderate 41 of 364 days1993: Unhealthy for Sensitive Groups 8 of 364 days1993: Unhealthy 3 of 364 days1994: Good 269 of 344 days1994: Moderate 58 of 344 days1994: Unhealthy for Sensitive Groups 14 of 344 days1994: Unhealthy 3 of 344 days1995: Good 195 of 268 days1995: Moderate 52 of 268 days1995: Unhealthy for Sensitive Groups 16 of 268 days1995: Unhealthy 5 of 268 days19951996: Good 220 of 275 days1996: Moderate 36 of 275 days1996: Unhealthy for Sensitive Groups 13 of 275 days1996: Unhealthy 6 of 275 days1997: Good 300 of 364 days1997: Moderate 50 of 364 days1997: Unhealthy for Sensitive Groups 12 of 364 days1997: Unhealthy 2 of 364 days1998: Good 241 of 347 days1998: Moderate 73 of 347 days1998: Unhealthy for Sensitive Groups 28 of 347 days1998: Unhealthy 5 of 347 days1999: Good 248 of 364 days1999: Moderate 82 of 364 days1999: Unhealthy for Sensitive Groups 22 of 364 days1999: Unhealthy 11 of 364 days1999: Very Unhealthy 1 of 364 days2000: Good 227 of 365 days2000: Moderate 125 of 365 days2000: Unhealthy for Sensitive Groups 11 of 365 days2000: Unhealthy 2 of 365 days20002001: Good 218 of 354 days2001: Moderate 109 of 354 days2001: Unhealthy for Sensitive Groups 19 of 354 days2001: Unhealthy 6 of 354 days2001: Very Unhealthy 2 of 354 days2002: Good 225 of 365 days2002: Moderate 109 of 365 days2002: Unhealthy for Sensitive Groups 20 of 365 days2002: Unhealthy 11 of 365 days2003: Good 224 of 358 days2003: Moderate 112 of 358 days2003: Unhealthy for Sensitive Groups 17 of 358 days2003: Unhealthy 4 of 358 days2003: Very Unhealthy 1 of 358 days2004: Good 256 of 351 days2004: Moderate 88 of 351 days2004: Unhealthy for Sensitive Groups 7 of 351 days2005: Good 218 of 361 days2005: Moderate 120 of 361 days2005: Unhealthy for Sensitive Groups 19 of 361 days2005: Unhealthy 4 of 361 days20052006: Good 251 of 364 days2006: Moderate 103 of 364 days2006: Unhealthy for Sensitive Groups 10 of 364 days2007: Good 243 of 364 days2007: Moderate 103 of 364 days2007: Unhealthy for Sensitive Groups 17 of 364 days2007: Unhealthy 1 of 364 days2008: Good 265 of 364 days2008: Moderate 95 of 364 days2008: Unhealthy for Sensitive Groups 4 of 364 days2009: Good 278 of 363 days2009: Moderate 85 of 363 days2010: Good 273 of 362 days2010: Moderate 88 of 362 days2010: Unhealthy for Sensitive Groups 1 of 362 days20102011: Good 261 of 357 days2011: Moderate 89 of 357 days2011: Unhealthy for Sensitive Groups 6 of 357 days2011: Unhealthy 1 of 357 days2012: Good 249 of 364 days2012: Moderate 93 of 364 days2012: Unhealthy for Sensitive Groups 20 of 364 days2012: Unhealthy 2 of 364 days2013: Good 282 of 364 days2013: Moderate 81 of 364 days2013: Unhealthy for Sensitive Groups 1 of 364 days2014: Good 174 of 365 days2014: Moderate 187 of 365 days2014: Unhealthy for Sensitive Groups 4 of 365 days2015: Good 190 of 365 days2015: Moderate 175 of 365 days20152016: Good 233 of 366 days2016: Moderate 127 of 366 days2016: Unhealthy for Sensitive Groups 6 of 366 days2017: Good 216 of 365 days2017: Moderate 146 of 365 days2017: Unhealthy for Sensitive Groups 3 of 365 days2018: Good 238 of 365 days2018: Moderate 121 of 365 days2018: Unhealthy for Sensitive Groups 6 of 365 days2019: Good 248 of 365 days2019: Moderate 117 of 365 days2020: Good 236 of 366 days2020: Moderate 124 of 366 days2020: Unhealthy for Sensitive Groups 5 of 366 days2020: Unhealthy 1 of 366 days20202021: Good 212 of 365 days2021: Moderate 153 of 365 days2022: Good 222 of 365 days2022: Moderate 142 of 365 days2022: Unhealthy for Sensitive Groups 1 of 365 days2023: Good 168 of 365 days2023: Moderate 184 of 365 days2023: Unhealthy for Sensitive Groups 9 of 365 days2023: Unhealthy 2 of 365 days2023: Very Unhealthy 2 of 365 days2024: Good 253 of 366 days2024: Moderate 113 of 366 days2025: Good 253 of 365 days2025: Moderate 104 of 365 days2025: Unhealthy for Sensitive Groups 7 of 365 days2025: Unhealthy 1 of 365 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 year0501001502001980: 90th percentile AQI 801981: 90th percentile AQI 471982: 90th percentile AQI 1011983: 90th percentile AQI 931984: 90th percentile AQI 841985: 90th percentile AQI 801986: 90th percentile AQI 741987: 90th percentile AQI 1051988: 90th percentile AQI 1561989: 90th percentile AQI 1051990: 90th percentile AQI 901991: 90th percentile AQI 1001992: 90th percentile AQI 671993: 90th percentile AQI 611994: 90th percentile AQI 801995: 90th percentile AQI 931996: 90th percentile AQI 841997: 90th percentile AQI 741998: 90th percentile AQI 1001999: 90th percentile AQI 972000: 90th percentile AQI 772001: 90th percentile AQI 932002: 90th percentile AQI 932003: 90th percentile AQI 872004: 90th percentile AQI 772005: 90th percentile AQI 932006: 90th percentile AQI 742007: 90th percentile AQI 742008: 90th percentile AQI 712009: 90th percentile AQI 642010: 90th percentile AQI 672011: 90th percentile AQI 712012: 90th percentile AQI 872013: 90th percentile AQI 612014: 90th percentile AQI 712015: 90th percentile AQI 672016: 90th percentile AQI 622017: 90th percentile AQI 642018: 90th percentile AQI 672019: 90th percentile AQI 612020: 90th percentile AQI 612021: 90th percentile AQI 652022: 90th percentile AQI 682023: 90th percentile AQI 762024: 90th percentile AQI 612025: 90th percentile AQI 681980: Median AQI 331981: Median AQI 291982: Median AQI 441983: Median AQI 401984: Median AQI 351985: Median AQI 381986: Median AQI 371987: Median AQI 441988: Median AQI 471989: Median AQI 441990: Median AQI 361991: Median AQI 351992: Median AQI 331993: Median AQI 341994: Median AQI 361995: Median AQI 391996: Median AQI 351997: Median AQI 311998: Median AQI 401999: Median AQI 422000: Median AQI 432001: Median AQI 432002: Median AQI 422003: Median AQI 422004: Median AQI 392005: Median AQI 442006: Median AQI 402007: Median AQI 402008: Median AQI 392009: Median AQI 372010: Median AQI 392011: Median AQI 392012: Median AQI 422013: Median AQI 382014: Median AQI 512015: Median AQI 492016: Median AQI 442017: Median AQI 462018: Median AQI 462019: Median AQI 442020: Median AQI 432021: Median AQI 462022: Median AQI 462023: Median AQI 522024: Median AQI 432025: Median AQI 411980198519901995200020052010201520202025
  • 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
Ozone22963%
Fine particles (PM2.5)13637%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536525310471004168152Ozone
20243662531130000436187Ozone
202336516818492205276218PM2.5
202236522214210004668101PM2.5
202136521215300004665100PM2.5
202036623612451004361160PM2.5
20193652481170000446189PM2.5
201836523812160004667150PM2.5
201736521614630004664119PM2.5
201636623312760004462122PM2.5
20153651901750000496799PM2.5
201436517418740005171126PM2.5
20133642828110003861101Ozone
201236424993202004287164Ozone
20113572618961003971154Ozone
20103622738810003967119Ozone
20093632788500003764100Ozone
20083642659540003971140Ozone
2007364243103171004074156Ozone
2006364251103100004074126Ozone
2005361218120194004493200Ozone
20043512568870003977147Ozone
2003358224112174104287201Ozone
20023652251092011004293179Ozone
2001354218109196204393203Ozone
2000365227125112004377161Ozone
1999364248822211104297201Ozone
1998347241732850040100185Ozone
199736430050122003174154Ozone
199627522036136003584174Ozone
199526819552165003993179Ozone
199434426958143003680174Ozone
19933643124183003461190Ozone
199236430443116003367200Ozone
19913602735225100035100185Ozone
199036428751197003690195Ozone
1989213143472030044105172Ozone
19882141224818224047156217Ozone
1987213148372431044105203Ozone
19861981613160003774143Ozone
19851661213771003880169Ozone
19841591233060003584126Ozone
198320514939161004093151Ozone
1982184119451910044101154Ozone
19812412221441002947169Ozone
198022618328114003380166Ozone

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 Michigan with a similar median AQI in 2025

All monitored counties in Michigan

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