EnviroNearby

Adams County, Colorado air quality history

Daily Air Quality Index summaries from EPA monitors in Adams, Colorado, 1980–2025.

55%
Good days in 2025
49
Median daily AQI, 2025
1
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 Adams, Colorado on 365 days. 201 of those days (55%) were in the Good range, and the median daily AQI was 49. That median is higher than the typical monitored county in Colorado (median 46 across 27 counties), and higher than the typical monitored U.S. county (40). The main pollutant was ozone on 182 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 49% in 1980–1982 versus 48% 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 127 of 340 days1980: Moderate 178 of 340 days1980: Unhealthy for Sensitive Groups 35 of 340 days19801981: Good 157 of 346 days1981: Moderate 147 of 346 days1981: Unhealthy for Sensitive Groups 40 of 346 days1981: Unhealthy 1 of 346 days1981: Very Unhealthy 1 of 346 days1982: Good 235 of 359 days1982: Moderate 108 of 359 days1982: Unhealthy for Sensitive Groups 16 of 359 days1983: Good 153 of 360 days1983: Moderate 145 of 360 days1983: Unhealthy for Sensitive Groups 60 of 360 days1983: Unhealthy 2 of 360 days1984: Good 182 of 363 days1984: Moderate 153 of 363 days1984: Unhealthy for Sensitive Groups 28 of 363 days1985: Good 161 of 357 days1985: Moderate 159 of 357 days1985: Unhealthy for Sensitive Groups 37 of 357 days19851986: Good 126 of 363 days1986: Moderate 176 of 363 days1986: Unhealthy for Sensitive Groups 58 of 363 days1986: Unhealthy 2 of 363 days1986: Very Unhealthy 1 of 363 days1987: Good 162 of 365 days1987: Moderate 170 of 365 days1987: Unhealthy for Sensitive Groups 28 of 365 days1987: Unhealthy 5 of 365 days1988: Good 198 of 366 days1988: Moderate 146 of 366 days1988: Unhealthy for Sensitive Groups 21 of 366 days1988: Unhealthy 1 of 366 days1989: Good 207 of 365 days1989: Moderate 134 of 365 days1989: Unhealthy for Sensitive Groups 24 of 365 days1990: Good 300 of 364 days1990: Moderate 63 of 364 days1990: Unhealthy for Sensitive Groups 1 of 364 days19901991: Good 203 of 365 days1991: Moderate 159 of 365 days1991: Unhealthy for Sensitive Groups 3 of 365 days1992: Good 177 of 356 days1992: Moderate 166 of 356 days1992: Unhealthy for Sensitive Groups 13 of 356 days1993: Good 187 of 365 days1993: Moderate 165 of 365 days1993: Unhealthy for Sensitive Groups 13 of 365 days1994: Good 139 of 365 days1994: Moderate 217 of 365 days1994: Unhealthy for Sensitive Groups 9 of 365 days1995: Good 228 of 365 days1995: Moderate 129 of 365 days1995: Unhealthy for Sensitive Groups 8 of 365 days19951996: Good 201 of 366 days1996: Moderate 154 of 366 days1996: Unhealthy for Sensitive Groups 11 of 366 days1997: Good 209 of 365 days1997: Moderate 145 of 365 days1997: Unhealthy for Sensitive Groups 11 of 365 days1998: Good 181 of 365 days1998: Moderate 168 of 365 days1998: Unhealthy for Sensitive Groups 14 of 365 days1998: Unhealthy 2 of 365 days1999: Good 159 of 365 days1999: Moderate 201 of 365 days1999: Unhealthy for Sensitive Groups 5 of 365 days2000: Good 189 of 366 days2000: Moderate 172 of 366 days2000: Unhealthy for Sensitive Groups 5 of 366 days20002001: Good 140 of 365 days2001: Moderate 221 of 365 days2001: Unhealthy for Sensitive Groups 3 of 365 days2001: Unhealthy 1 of 365 days2002: Good 190 of 365 days2002: Moderate 173 of 365 days2002: Unhealthy for Sensitive Groups 2 of 365 days2003: Good 207 of 364 days2003: Moderate 153 of 364 days2003: Unhealthy for Sensitive Groups 4 of 364 days2004: Good 203 of 366 days2004: Moderate 158 of 366 days2004: Unhealthy for Sensitive Groups 5 of 366 days2005: Good 185 of 365 days2005: Moderate 173 of 365 days2005: Unhealthy for Sensitive Groups 7 of 365 days20052006: Good 189 of 365 days2006: Moderate 172 of 365 days2006: Unhealthy for Sensitive Groups 2 of 365 days2006: Unhealthy 2 of 365 days2007: Good 161 of 365 days2007: Moderate 197 of 365 days2007: Unhealthy for Sensitive Groups 5 of 365 days2007: Unhealthy 2 of 365 days2008: Good 189 of 366 days2008: Moderate 162 of 366 days2008: Unhealthy for Sensitive Groups 15 of 366 days2009: Good 223 of 365 days2009: Moderate 136 of 365 days2009: Unhealthy for Sensitive Groups 6 of 365 days2010: Good 259 of 363 days2010: Moderate 104 of 363 days20102011: Good 193 of 365 days2011: Moderate 159 of 365 days2011: Unhealthy for Sensitive Groups 12 of 365 days2011: Unhealthy 1 of 365 days2012: Good 213 of 366 days2012: Moderate 145 of 366 days2012: Unhealthy for Sensitive Groups 7 of 366 days2012: Unhealthy 1 of 366 days2013: Good 207 of 365 days2013: Moderate 143 of 365 days2013: Unhealthy for Sensitive Groups 15 of 365 days2014: Good 222 of 365 days2014: Moderate 138 of 365 days2014: Unhealthy for Sensitive Groups 5 of 365 days2015: Good 266 of 365 days2015: Moderate 96 of 365 days2015: Unhealthy for Sensitive Groups 3 of 365 days20152016: Good 236 of 366 days2016: Moderate 129 of 366 days2016: Unhealthy for Sensitive Groups 1 of 366 days2017: Good 160 of 365 days2017: Moderate 203 of 365 days2017: Unhealthy for Sensitive Groups 2 of 365 days2018: Good 138 of 365 days2018: Moderate 224 of 365 days2018: Unhealthy for Sensitive Groups 3 of 365 days2019: Good 183 of 365 days2019: Moderate 181 of 365 days2019: Unhealthy for Sensitive Groups 1 of 365 days2020: Good 192 of 366 days2020: Moderate 162 of 366 days2020: Unhealthy for Sensitive Groups 11 of 366 days2020: Unhealthy 1 of 366 days20202021: Good 188 of 365 days2021: Moderate 154 of 365 days2021: Unhealthy for Sensitive Groups 22 of 365 days2021: Unhealthy 1 of 365 days2022: Good 180 of 365 days2022: Moderate 171 of 365 days2022: Unhealthy for Sensitive Groups 14 of 365 days2023: Good 179 of 365 days2023: Moderate 181 of 365 days2023: Unhealthy for Sensitive Groups 3 of 365 days2023: Unhealthy 2 of 365 days2024: Good 147 of 366 days2024: Moderate 197 of 366 days2024: Unhealthy for Sensitive Groups 20 of 366 days2024: Unhealthy 2 of 366 days2025: Good 201 of 365 days2025: Moderate 163 of 365 days2025: Unhealthy for Sensitive Groups 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 year0501001501980: 90th percentile AQI 1011981: 90th percentile AQI 1021982: 90th percentile AQI 811983: 90th percentile AQI 1061984: 90th percentile AQI 941985: 90th percentile AQI 1011986: 90th percentile AQI 1041987: 90th percentile AQI 941988: 90th percentile AQI 871989: 90th percentile AQI 891990: 90th percentile AQI 631991: 90th percentile AQI 741992: 90th percentile AQI 811993: 90th percentile AQI 841994: 90th percentile AQI 801995: 90th percentile AQI 671996: 90th percentile AQI 821997: 90th percentile AQI 721998: 90th percentile AQI 831999: 90th percentile AQI 772000: 90th percentile AQI 672001: 90th percentile AQI 722002: 90th percentile AQI 712003: 90th percentile AQI 712004: 90th percentile AQI 682005: 90th percentile AQI 772006: 90th percentile AQI 722007: 90th percentile AQI 802008: 90th percentile AQI 842009: 90th percentile AQI 742010: 90th percentile AQI 612011: 90th percentile AQI 802012: 90th percentile AQI 762013: 90th percentile AQI 872014: 90th percentile AQI 712015: 90th percentile AQI 642016: 90th percentile AQI 652017: 90th percentile AQI 732018: 90th percentile AQI 742019: 90th percentile AQI 672020: 90th percentile AQI 742021: 90th percentile AQI 932022: 90th percentile AQI 842023: 90th percentile AQI 712024: 90th percentile AQI 932025: 90th percentile AQI 711980: Median AQI 581981: Median AQI 541982: Median AQI 441983: Median AQI 561984: Median AQI 501985: Median AQI 541986: Median AQI 641987: Median AQI 541988: Median AQI 491989: Median AQI 491990: Median AQI 391991: Median AQI 481992: Median AQI 511993: Median AQI 501994: Median AQI 551995: Median AQI 461996: Median AQI 491997: Median AQI 471998: Median AQI 511999: Median AQI 522000: Median AQI 502001: Median AQI 542002: Median AQI 502003: Median AQI 492004: Median AQI 492005: Median AQI 502006: Median AQI 502007: Median AQI 532008: Median AQI 492009: Median AQI 472010: Median AQI 442011: Median AQI 502012: Median AQI 492013: Median AQI 482014: Median AQI 482015: Median AQI 452016: Median AQI 462017: Median AQI 522018: Median AQI 542019: Median AQI 502020: Median AQI 492021: Median AQI 492022: Median AQI 512023: Median AQI 512024: Median AQI 552025: Median AQI 491980198519901995200020052010201520202025
  • 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
Ozone18250%
Fine particles (PM2.5)9225%
Coarse particles (PM10)5816%
Nitrogen dioxide (NO₂)339%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536520116310004971112Ozone
2024366147197202005593161Ozone
202336517918132005171174Ozone
2022365180171140005184126Ozone
2021365188154221004993151Ozone
2020366192162111004974151Ozone
201936518318110005067132PM2.5
201836513822430005474130PM2.5
201736516020320005273132PM2.5
201636623612910004665105Ozone
20153652669630004564115Ozone
201436522213850004871124Ozone
2013365207143150004887140Ozone
201236621314571004976154Ozone
2011365193159121005080159Ozone
20103632591040000446193Ozone
200936522313660004774126Ozone
2008366189162150004984150Ozone
200736516119752005380164Ozone
200636518917222005072183Ozone
200536518517370005077119Ozone
200436620315850004968134NO2
200336420715340004971144NO2
200236519017320005071112Ozone
200136514022131005472152NO2
200036618917250005067114PM10
199936515920150005277136NO2
1998365181168142005183174NO2
1997365209145110004772136NO2
1996366201154110004982133Ozone
199536522812980004667127NO2
199436513921790005580122NO2
1993365187165130005084147Ozone
1992356177166130005181129NO2
199136520315930004874108Ozone
19903643006310003963108Ozone
1989365207134240004989122NO2
1988366198146211004987151NO2
1987365162170285005494187NO2
19863631261765821064104210NO2
19853571611593700054101148NO2
1984363182153280005094150Ozone
19833601531456020056106161NO2
1982359235108160004481115Ozone
19813461571474011054102209NO2
19803401271783500058101150Ozone

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 Colorado with a similar median AQI in 2025

All monitored counties in Colorado

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