EnviroNearby

Arapahoe County, Colorado air quality history

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

58%
Good days in 2025
48
Median daily AQI, 2025
2
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 Arapahoe, Colorado on 365 days. 212 of those days (58%) were in the Good range, and the median daily AQI was 48. That median is about the same as 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 312 days. Across the years with fuller monitoring, the share of Good days fell: an average of 66% in 1980–1982 versus 59% 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 308 of 362 days1980: Moderate 49 of 362 days1980: Unhealthy for Sensitive Groups 4 of 362 days1980: Unhealthy 1 of 362 days19801981: Good 232 of 364 days1981: Moderate 103 of 364 days1981: Unhealthy for Sensitive Groups 24 of 364 days1981: Unhealthy 5 of 364 days1982: Good 178 of 363 days1982: Moderate 137 of 363 days1982: Unhealthy for Sensitive Groups 40 of 363 days1982: Unhealthy 7 of 363 days1982: Very Unhealthy 1 of 363 days1983: Good 175 of 365 days1983: Moderate 150 of 365 days1983: Unhealthy for Sensitive Groups 31 of 365 days1983: Unhealthy 8 of 365 days1983: Very Unhealthy 1 of 365 days1984: Good 204 of 366 days1984: Moderate 134 of 366 days1984: Unhealthy for Sensitive Groups 26 of 366 days1984: Unhealthy 2 of 366 days1985: Good 224 of 364 days1985: Moderate 128 of 364 days1985: Unhealthy for Sensitive Groups 12 of 364 days19851986: Good 189 of 365 days1986: Moderate 154 of 365 days1986: Unhealthy for Sensitive Groups 20 of 365 days1986: Unhealthy 2 of 365 days1987: Good 181 of 365 days1987: Moderate 140 of 365 days1987: Unhealthy for Sensitive Groups 39 of 365 days1987: Unhealthy 4 of 365 days1987: Very Unhealthy 1 of 365 days1988: Good 156 of 366 days1988: Moderate 151 of 366 days1988: Unhealthy for Sensitive Groups 42 of 366 days1988: Unhealthy 17 of 366 days1989: Good 235 of 365 days1989: Moderate 104 of 365 days1989: Unhealthy for Sensitive Groups 24 of 365 days1989: Unhealthy 2 of 365 days1990: Good 262 of 365 days1990: Moderate 86 of 365 days1990: Unhealthy for Sensitive Groups 15 of 365 days1990: Unhealthy 2 of 365 days19901991: Good 166 of 365 days1991: Moderate 180 of 365 days1991: Unhealthy for Sensitive Groups 18 of 365 days1991: Unhealthy 1 of 365 days1992: Good 194 of 366 days1992: Moderate 165 of 366 days1992: Unhealthy for Sensitive Groups 7 of 366 days1993: Good 246 of 365 days1993: Moderate 109 of 365 days1993: Unhealthy for Sensitive Groups 10 of 365 days1994: Good 216 of 365 days1994: Moderate 136 of 365 days1994: Unhealthy for Sensitive Groups 13 of 365 days1995: Good 227 of 365 days1995: Moderate 133 of 365 days1995: Unhealthy for Sensitive Groups 5 of 365 days19951996: Good 264 of 365 days1996: Moderate 92 of 365 days1996: Unhealthy for Sensitive Groups 9 of 365 days1997: Good 309 of 361 days1997: Moderate 51 of 361 days1997: Unhealthy for Sensitive Groups 1 of 361 days1998: Good 241 of 349 days1998: Moderate 93 of 349 days1998: Unhealthy for Sensitive Groups 14 of 349 days1998: Unhealthy 1 of 349 days1999: Good 252 of 359 days1999: Moderate 96 of 359 days1999: Unhealthy for Sensitive Groups 10 of 359 days1999: Very Unhealthy 1 of 359 days2000: Good 237 of 362 days2000: Moderate 108 of 362 days2000: Unhealthy for Sensitive Groups 16 of 362 days2000: Unhealthy 1 of 362 days20002001: Good 234 of 345 days2001: Moderate 100 of 345 days2001: Unhealthy for Sensitive Groups 11 of 345 days2002: Good 221 of 356 days2002: Moderate 118 of 356 days2002: Unhealthy for Sensitive Groups 15 of 356 days2002: Unhealthy 2 of 356 days2003: Good 238 of 354 days2003: Moderate 86 of 354 days2003: Unhealthy for Sensitive Groups 26 of 354 days2003: Unhealthy 2 of 354 days2003: Very Unhealthy 2 of 354 days2004: Good 264 of 362 days2004: Moderate 92 of 362 days2004: Unhealthy for Sensitive Groups 6 of 362 days2005: Good 239 of 356 days2005: Moderate 97 of 356 days2005: Unhealthy for Sensitive Groups 19 of 356 days2005: Unhealthy 1 of 356 days20052006: Good 210 of 357 days2006: Moderate 115 of 357 days2006: Unhealthy for Sensitive Groups 32 of 357 days2007: Good 234 of 360 days2007: Moderate 115 of 360 days2007: Unhealthy for Sensitive Groups 10 of 360 days2007: Unhealthy 1 of 360 days2008: Good 153 of 190 days2008: Moderate 37 of 190 days2009: Good 242 of 338 days2009: Moderate 92 of 338 days2009: Unhealthy for Sensitive Groups 4 of 338 days2010: Good 216 of 365 days2010: Moderate 142 of 365 days2010: Unhealthy for Sensitive Groups 7 of 365 days20102011: Good 202 of 364 days2011: Moderate 139 of 364 days2011: Unhealthy for Sensitive Groups 20 of 364 days2011: Unhealthy 3 of 364 days2012: Good 199 of 365 days2012: Moderate 142 of 365 days2012: Unhealthy for Sensitive Groups 22 of 365 days2012: Unhealthy 2 of 365 days2013: Good 206 of 365 days2013: Moderate 141 of 365 days2013: Unhealthy for Sensitive Groups 18 of 365 days2014: Good 261 of 364 days2014: Moderate 102 of 364 days2014: Unhealthy for Sensitive Groups 1 of 364 days2015: Good 257 of 361 days2015: Moderate 102 of 361 days2015: Unhealthy for Sensitive Groups 2 of 361 days20152016: Good 261 of 366 days2016: Moderate 99 of 366 days2016: Unhealthy for Sensitive Groups 6 of 366 days2017: Good 221 of 365 days2017: Moderate 137 of 365 days2017: Unhealthy for Sensitive Groups 7 of 365 days2018: Good 227 of 365 days2018: Moderate 123 of 365 days2018: Unhealthy for Sensitive Groups 14 of 365 days2018: Unhealthy 1 of 365 days2019: Good 222 of 365 days2019: Moderate 137 of 365 days2019: Unhealthy for Sensitive Groups 6 of 365 days2020: Good 243 of 366 days2020: Moderate 112 of 366 days2020: Unhealthy for Sensitive Groups 9 of 366 days2020: Unhealthy 2 of 366 days20202021: Good 220 of 365 days2021: Moderate 108 of 365 days2021: Unhealthy for Sensitive Groups 34 of 365 days2021: Unhealthy 3 of 365 days2022: Good 237 of 365 days2022: Moderate 116 of 365 days2022: Unhealthy for Sensitive Groups 12 of 365 days2023: Good 239 of 365 days2023: Moderate 118 of 365 days2023: Unhealthy for Sensitive Groups 8 of 365 days2024: Good 196 of 366 days2024: Moderate 153 of 366 days2024: Unhealthy for Sensitive Groups 15 of 366 days2024: Unhealthy 2 of 366 days2025: Good 212 of 365 days2025: Moderate 151 of 365 days2025: Unhealthy for Sensitive Groups 2 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 581981: 90th percentile AQI 971982: 90th percentile AQI 1081983: 90th percentile AQI 1041984: 90th percentile AQI 901985: 90th percentile AQI 801986: 90th percentile AQI 911987: 90th percentile AQI 1031988: 90th percentile AQI 1151989: 90th percentile AQI 871990: 90th percentile AQI 841991: 90th percentile AQI 871992: 90th percentile AQI 771993: 90th percentile AQI 741994: 90th percentile AQI 791995: 90th percentile AQI 741996: 90th percentile AQI 771997: 90th percentile AQI 541998: 90th percentile AQI 841999: 90th percentile AQI 742000: 90th percentile AQI 872001: 90th percentile AQI 802002: 90th percentile AQI 902003: 90th percentile AQI 912004: 90th percentile AQI 712005: 90th percentile AQI 872006: 90th percentile AQI 1002007: 90th percentile AQI 842008: 90th percentile AQI 562009: 90th percentile AQI 712010: 90th percentile AQI 802011: 90th percentile AQI 872012: 90th percentile AQI 932013: 90th percentile AQI 872014: 90th percentile AQI 612015: 90th percentile AQI 672016: 90th percentile AQI 712017: 90th percentile AQI 842018: 90th percentile AQI 872019: 90th percentile AQI 802020: 90th percentile AQI 772021: 90th percentile AQI 1012022: 90th percentile AQI 842023: 90th percentile AQI 742024: 90th percentile AQI 872025: 90th percentile AQI 711980: Median AQI 381981: Median AQI 461982: Median AQI 511983: Median AQI 521984: Median AQI 491985: Median AQI 471986: Median AQI 501987: Median AQI 511988: Median AQI 571989: Median AQI 451990: Median AQI 411991: Median AQI 511992: Median AQI 501993: Median AQI 461994: Median AQI 481995: Median AQI 471996: Median AQI 421997: Median AQI 341998: Median AQI 421999: Median AQI 432000: Median AQI 442001: Median AQI 432002: Median AQI 442003: Median AQI 452004: Median AQI 432005: Median AQI 442006: Median AQI 452007: Median AQI 442008: Median AQI 392009: Median AQI 442010: Median AQI 482011: Median AQI 492012: Median AQI 482013: Median AQI 472014: Median AQI 452015: Median AQI 452016: Median AQI 442017: Median AQI 472018: Median AQI 462019: Median AQI 472020: Median AQI 462021: Median AQI 462022: Median AQI 462023: Median AQI 472024: Median AQI 492025: Median AQI 481980198519901995200020052010201520202025
  • 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
Ozone31285%
Fine particles (PM2.5)5315%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536521215120004871101Ozone
2024366196153152004987161Ozone
202336523911880004774136Ozone
2022365237116120004684129Ozone
20213652201083430046101161Ozone
202036624311292004677159Ozone
201936522213760004780140Ozone
2018365227123141004687156Ozone
201736522113770004784119Ozone
20163662619960004471119Ozone
201536125710220004567136Ozone
201436426110210004561122Ozone
2013365206141180004787150Ozone
2012365199142222004893172Ozone
2011364202139203004987159Ozone
201036521614270004880122Ozone
20093382429240004471129Ozone
2008190153370000395674PM2.5
2007360234115101004484154Ozone
20063572101153200045100150Ozone
200535623997191004487151Ozone
20043622649260004371119Ozone
200335423886262204591215Ozone
2002356221118152004490151Ozone
2001345234100110004380140Ozone
2000362237108161004487151Ozone
199935925296100104374216Ozone
199834924193141004284177Ozone
19973613095110003454115Ozone
19963652649290004277140Ozone
199536522713350004774115NO2
1994365216136130004879147NO2
1993365246109100004674136NO2
199236619416570005077147NO2
1991365166180181005187166Ozone
199036526286152004184151Ozone
1989365235104242004587166Ozone
198836615615142170057115200Ozone
19873651811403941051103204Ozone
1986365189154202005091190Ozone
1985364224128120004780140Ozone
1984366204134262004990159Ozone
19833651751503181052104207Ozone
19823631781374071051108204Ozone
1981364232103245004697177Ozone
19803623084941003858161Ozone

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