EnviroNearby

Teller County, Colorado air quality history

Daily Air Quality Index summaries from EPA monitors in Teller, Colorado, 1994–2018.

39%
Good days in 2018
58
Median daily AQI, 2018
12
Days above 100 in 2018
160
Days with an AQI in 2018 (of 365)

In 2018, EPA reported a daily Air Quality Index (AQI) for Teller, Colorado on 160 days. 63 of those days (39%) were in the Good range, and the median daily AQI was 58. That median is higher than the typical monitored county in Colorado (median 47 across 30 counties), and higher than the typical monitored U.S. county (41). The main pollutant was ozone on 160 days. Across the years with fuller monitoring, the share of Good days fell: an average of 76% in 1996–1998 versus 63% in 2006–2018.

EPA did not report an AQI for every day of 2018 here (160 of 365 days). Figures describe monitored days only; seasonal monitoring (for example, ozone measured only in warmer months) can make a county look cleaner or dirtier than a full-year record would.

The most recent year with data for this county is 2018; EPA's files for 2019–2025 contain no row for it, which usually means its monitors stopped reporting.

Years with fewer than 120 monitored days (1994, 1995, 2008) are shown in the table but left out of comparisons and trend statements.

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%1994: Good 9 of 12 days1994: Moderate 3 of 12 days19941995: Good 67 of 96 days1995: Moderate 23 of 96 days1995: Unhealthy for Sensitive Groups 4 of 96 days1995: Unhealthy 2 of 96 days1996: Good 253 of 316 days1996: Moderate 59 of 316 days1996: Unhealthy for Sensitive Groups 4 of 316 days19961997: Good 164 of 228 days1997: Moderate 64 of 228 days1998: Good 187 of 249 days1998: Moderate 62 of 249 days19981999: Good 241 of 260 days1999: Moderate 19 of 260 days2000: Good 275 of 297 days2000: Moderate 22 of 297 days20002001: Good 284 of 287 days2001: Moderate 3 of 287 days2002: Good 331 of 348 days2002: Moderate 17 of 348 days20022003: Good 334 of 336 days2003: Moderate 2 of 336 days2004: Good 344 of 346 days2004: Moderate 2 of 346 days20042005: Good 360 of 360 days2006: Good 350 of 350 days20062008: Good 20 of 82 days2008: Moderate 48 of 82 days2008: Unhealthy for Sensitive Groups 14 of 82 days2010: Good 63 of 130 days2010: Moderate 65 of 130 days2010: Unhealthy for Sensitive Groups 2 of 130 days20102018: Good 63 of 160 days2018: Moderate 85 of 160 days2018: Unhealthy for Sensitive Groups 12 of 160 days2018
  • 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 year0501001501994: 90th percentile AQI 841995: 90th percentile AQI 761996: 90th percentile AQI 581997: 90th percentile AQI 621998: 90th percentile AQI 631999: 90th percentile AQI 472000: 90th percentile AQI 462001: 90th percentile AQI 312002: 90th percentile AQI 422003: 90th percentile AQI 312004: 90th percentile AQI 292005: 90th percentile AQI 282006: 90th percentile AQI 232008: 90th percentile AQI 1122010: 90th percentile AQI 842018: 90th percentile AQI 971994: Median AQI 441995: Median AQI 361996: Median AQI 281997: Median AQI 331998: Median AQI 321999: Median AQI 242000: Median AQI 212001: Median AQI 202002: Median AQI 222003: Median AQI 192004: Median AQI 172005: Median AQI 162006: Median AQI 142008: Median AQI 742010: Median AQI 512018: Median AQI 58199419961998200020022004200620102018
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2018

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
Ozone160100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20181606385120005897133Ozone
2010130636520005184105Ozone
20088220481400074112140Ozone
200635035000000142343PM10
200536036000000162846PM10
200434634420000172972PM10
200333633420000193156PM10
2002348331170000224278PM10
200128728430000203157PM10
2000297275220000214681PM10
1999260241190000244771PM10
1998249187620000326393PM10
1997228164640000336291PM10
19963162535940002858141PM10
199596672342003676176PM10
199412930000448493PM10

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 2018

All monitored counties in Colorado

Source: U.S. EPA AirData, “Annual AQI by County” files for 1994–2018 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem