EnviroNearby

Denver County, Colorado air quality history

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

50%
Good days in 2025
50
Median daily AQI, 2025
6
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 Denver, Colorado on 365 days. 184 of those days (50%) were in the Good range, and the median daily AQI was 50. 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 179 days. Across the years with fuller monitoring, the share of Good days rose: an average of 6% in 1980–1982 versus 41% 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 14 of 363 days1980: Moderate 223 of 363 days1980: Unhealthy for Sensitive Groups 100 of 363 days1980: Unhealthy 16 of 363 days1980: Very Unhealthy 10 of 363 days19801981: Good 16 of 364 days1981: Moderate 242 of 364 days1981: Unhealthy for Sensitive Groups 63 of 364 days1981: Unhealthy 25 of 364 days1981: Very Unhealthy 16 of 364 days1981: Hazardous 2 of 364 days1982: Good 35 of 365 days1982: Moderate 223 of 365 days1982: Unhealthy for Sensitive Groups 73 of 365 days1982: Unhealthy 23 of 365 days1982: Very Unhealthy 11 of 365 days1983: Good 38 of 365 days1983: Moderate 192 of 365 days1983: Unhealthy for Sensitive Groups 105 of 365 days1983: Unhealthy 16 of 365 days1983: Very Unhealthy 14 of 365 days1984: Good 37 of 365 days1984: Moderate 227 of 365 days1984: Unhealthy for Sensitive Groups 72 of 365 days1984: Unhealthy 21 of 365 days1984: Very Unhealthy 8 of 365 days1985: Good 54 of 365 days1985: Moderate 221 of 365 days1985: Unhealthy for Sensitive Groups 78 of 365 days1985: Unhealthy 4 of 365 days1985: Very Unhealthy 7 of 365 days1985: Hazardous 1 of 365 days19851986: Good 25 of 365 days1986: Moderate 250 of 365 days1986: Unhealthy for Sensitive Groups 73 of 365 days1986: Unhealthy 11 of 365 days1986: Very Unhealthy 6 of 365 days1987: Good 74 of 365 days1987: Moderate 213 of 365 days1987: Unhealthy for Sensitive Groups 57 of 365 days1987: Unhealthy 15 of 365 days1987: Very Unhealthy 6 of 365 days1988: Good 72 of 366 days1988: Moderate 233 of 366 days1988: Unhealthy for Sensitive Groups 49 of 366 days1988: Unhealthy 10 of 366 days1988: Very Unhealthy 2 of 366 days1989: Good 119 of 365 days1989: Moderate 204 of 365 days1989: Unhealthy for Sensitive Groups 41 of 365 days1989: Unhealthy 1 of 365 days1990: Good 245 of 365 days1990: Moderate 112 of 365 days1990: Unhealthy for Sensitive Groups 8 of 365 days19901991: Good 234 of 365 days1991: Moderate 117 of 365 days1991: Unhealthy for Sensitive Groups 12 of 365 days1991: Unhealthy 2 of 365 days1992: Good 111 of 366 days1992: Moderate 224 of 366 days1992: Unhealthy for Sensitive Groups 27 of 366 days1992: Unhealthy 3 of 366 days1992: Very Unhealthy 1 of 366 days1993: Good 168 of 365 days1993: Moderate 182 of 365 days1993: Unhealthy for Sensitive Groups 15 of 365 days1994: Good 127 of 365 days1994: Moderate 227 of 365 days1994: Unhealthy for Sensitive Groups 11 of 365 days1995: Good 166 of 365 days1995: Moderate 190 of 365 days1995: Unhealthy for Sensitive Groups 9 of 365 days19951996: Good 145 of 366 days1996: Moderate 214 of 366 days1996: Unhealthy for Sensitive Groups 7 of 366 days1997: Good 168 of 365 days1997: Moderate 191 of 365 days1997: Unhealthy for Sensitive Groups 6 of 365 days1998: Good 119 of 365 days1998: Moderate 232 of 365 days1998: Unhealthy for Sensitive Groups 11 of 365 days1998: Unhealthy 3 of 365 days1999: Good 214 of 365 days1999: Moderate 148 of 365 days1999: Unhealthy for Sensitive Groups 3 of 365 days2000: Good 143 of 366 days2000: Moderate 217 of 366 days2000: Unhealthy for Sensitive Groups 6 of 366 days20002001: Good 83 of 365 days2001: Moderate 263 of 365 days2001: Unhealthy for Sensitive Groups 17 of 365 days2001: Unhealthy 2 of 365 days2002: Good 103 of 365 days2002: Moderate 250 of 365 days2002: Unhealthy for Sensitive Groups 12 of 365 days2003: Good 130 of 365 days2003: Moderate 214 of 365 days2003: Unhealthy for Sensitive Groups 18 of 365 days2003: Unhealthy 2 of 365 days2003: Very Unhealthy 1 of 365 days2004: Good 188 of 366 days2004: Moderate 175 of 366 days2004: Unhealthy for Sensitive Groups 3 of 366 days2005: Good 142 of 365 days2005: Moderate 211 of 365 days2005: Unhealthy for Sensitive Groups 12 of 365 days20052006: Good 132 of 365 days2006: Moderate 218 of 365 days2006: Unhealthy for Sensitive Groups 14 of 365 days2006: Unhealthy 1 of 365 days2007: Good 131 of 365 days2007: Moderate 218 of 365 days2007: Unhealthy for Sensitive Groups 15 of 365 days2007: Unhealthy 1 of 365 days2008: Good 174 of 366 days2008: Moderate 187 of 366 days2008: Unhealthy for Sensitive Groups 4 of 366 days2008: Unhealthy 1 of 366 days2009: Good 230 of 365 days2009: Moderate 135 of 365 days2010: Good 175 of 365 days2010: Moderate 187 of 365 days2010: Unhealthy for Sensitive Groups 3 of 365 days20102011: Good 169 of 365 days2011: Moderate 186 of 365 days2011: Unhealthy for Sensitive Groups 9 of 365 days2011: Unhealthy 1 of 365 days2012: Good 147 of 366 days2012: Moderate 203 of 366 days2012: Unhealthy for Sensitive Groups 14 of 366 days2012: Unhealthy 2 of 366 days2013: Good 163 of 365 days2013: Moderate 196 of 365 days2013: Unhealthy for Sensitive Groups 6 of 365 days2014: Good 152 of 365 days2014: Moderate 210 of 365 days2014: Unhealthy for Sensitive Groups 2 of 365 days2014: Unhealthy 1 of 365 days2015: Good 119 of 365 days2015: Moderate 237 of 365 days2015: Unhealthy for Sensitive Groups 9 of 365 days20152016: Good 127 of 366 days2016: Moderate 235 of 366 days2016: Unhealthy for Sensitive Groups 4 of 366 days2017: Good 149 of 365 days2017: Moderate 214 of 365 days2017: Unhealthy for Sensitive Groups 2 of 365 days2018: Good 124 of 365 days2018: Moderate 231 of 365 days2018: Unhealthy for Sensitive Groups 10 of 365 days2019: Good 139 of 365 days2019: Moderate 223 of 365 days2019: Unhealthy for Sensitive Groups 2 of 365 days2019: Unhealthy 1 of 365 days2020: Good 137 of 366 days2020: Moderate 212 of 366 days2020: Unhealthy for Sensitive Groups 17 of 366 days20202021: Good 128 of 365 days2021: Moderate 202 of 365 days2021: Unhealthy for Sensitive Groups 31 of 365 days2021: Unhealthy 4 of 365 days2022: Good 161 of 365 days2022: Moderate 197 of 365 days2022: Unhealthy for Sensitive Groups 7 of 365 days2023: Good 131 of 365 days2023: Moderate 228 of 365 days2023: Unhealthy for Sensitive Groups 4 of 365 days2023: Unhealthy 2 of 365 days2024: Good 129 of 366 days2024: Moderate 208 of 366 days2024: Unhealthy for Sensitive Groups 26 of 366 days2024: Unhealthy 3 of 366 days2025: Good 184 of 365 days2025: Moderate 175 of 365 days2025: Unhealthy for Sensitive Groups 6 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 1431981: 90th percentile AQI 1651982: 90th percentile AQI 1501983: 90th percentile AQI 1481984: 90th percentile AQI 1311985: 90th percentile AQI 1191986: 90th percentile AQI 1161987: 90th percentile AQI 1211988: 90th percentile AQI 1121989: 90th percentile AQI 1021990: 90th percentile AQI 771991: 90th percentile AQI 781992: 90th percentile AQI 971993: 90th percentile AQI 781994: 90th percentile AQI 831995: 90th percentile AQI 771996: 90th percentile AQI 791997: 90th percentile AQI 771998: 90th percentile AQI 831999: 90th percentile AQI 702000: 90th percentile AQI 832001: 90th percentile AQI 862002: 90th percentile AQI 812003: 90th percentile AQI 932004: 90th percentile AQI 672005: 90th percentile AQI 832006: 90th percentile AQI 842007: 90th percentile AQI 842008: 90th percentile AQI 802009: 90th percentile AQI 622010: 90th percentile AQI 742011: 90th percentile AQI 842012: 90th percentile AQI 842013: 90th percentile AQI 722014: 90th percentile AQI 742015: 90th percentile AQI 772016: 90th percentile AQI 742017: 90th percentile AQI 742018: 90th percentile AQI 802019: 90th percentile AQI 772020: 90th percentile AQI 802021: 90th percentile AQI 1002022: 90th percentile AQI 772023: 90th percentile AQI 772024: 90th percentile AQI 932025: 90th percentile AQI 741980: Median AQI 871981: Median AQI 821982: Median AQI 771983: Median AQI 841984: Median AQI 771985: Median AQI 771986: Median AQI 771987: Median AQI 711988: Median AQI 641989: Median AQI 601990: Median AQI 451991: Median AQI 441992: Median AQI 601993: Median AQI 521994: Median AQI 561995: Median AQI 521996: Median AQI 551997: Median AQI 521998: Median AQI 561999: Median AQI 482000: Median AQI 532001: Median AQI 572002: Median AQI 552003: Median AQI 562004: Median AQI 502005: Median AQI 532006: Median AQI 542007: Median AQI 542008: Median AQI 512009: Median AQI 472010: Median AQI 512011: Median AQI 522012: Median AQI 542013: Median AQI 522014: Median AQI 532015: Median AQI 542016: Median AQI 542017: Median AQI 532018: Median AQI 542019: Median AQI 542020: Median AQI 532021: Median AQI 552022: Median AQI 522023: Median AQI 542024: Median AQI 552025: Median AQI 501980198519901995200020052010201520202025
  • 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
Ozone17949%
Fine particles (PM2.5)11532%
Nitrogen dioxide (NO₂)7119%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536518417560005074115Ozone
2024366129208263005593172Ozone
202336513122842005477179Ozone
202236516119770005277112Ozone
20213651282023140055100166Ozone
2020366137212170005380150PM2.5
201936513922321005477153PM2.5
2018365124231100005480150PM2.5
201736514921420005374128NO2
201636612723540005474112NO2
201536511923790005477146PM2.5
201436515221021005374152PM2.5
201336516319660005272133PM2.5
2012366147203142005484166Ozone
201136516918691005284161Ozone
201036517518730005174108Ozone
200936523013500004762100Ozone
200836617418741005180151Ozone
2007365131218151005484155PM2.5
2006365132218141005484166PM2.5
2005365142211120005383133PM2.5
200436618817530005067113PM2.5
2003365130214182105693203NO2
2002365103250120005581143NO2
200136583263172005786160NO2
200036614321760005383126PM2.5
199936521414830004870122Ozone
1998365119232113005683156NO2
199736516819160005277119NO2
199636614521470005579126NO2
199536516619090005277136NO2
1994365127227110005683113NO2
1993365168182150005278119NO2
1992366111224273106097203NO2
1991365234117122004478158Ozone
199036524511280004577147Ozone
19893651192044110060102168NO2
19883667223349102064112222NO2
19873657421357156071121236NO2
19863652525073116077116271NO2
1985365542217847177119420NO2
19843653722772218077131236NO2
1983365381921051614084148265NO2
198236535223732311077150236CO
198136416242632516282165331CO
1980363142231001610087143244CO

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