EnviroNearby

Summit County, Colorado air quality history

Daily Air Quality Index summaries from EPA monitors in Summit, Colorado, 1992–2012.

97%
Good days in 2012
12
Median daily AQI, 2012
0
Days above 100 in 2012
123
Days with an AQI in 2012 (of 366)

In 2012, EPA reported a daily Air Quality Index (AQI) for Summit, Colorado on 123 days. 119 of those days (97%) were in the Good range, and the median daily AQI was 12. That median is lower than the typical monitored county in Colorado (median 47 across 27 counties), and lower than the typical monitored U.S. county (44). The main pollutant was coarse particles (PM10) on 123 days. Across the years with fuller monitoring, the share of Good days rose: an average of 95% in 1999–2001 versus 98% in 2010–2012.

EPA did not report an AQI for every day of 2012 here (123 of 366 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 2012; EPA's files for 2013–2025 contain no row for it, which usually means its monitors stopped reporting.

Years with fewer than 120 monitored days (1993, 1994, 1995, 1996, 1997, 1998…) 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%1992: Good 28 of 29 days1992: Moderate 1 of 29 days19921993: Good 49 of 56 days1993: Moderate 7 of 56 days1994: Good 45 of 52 days1994: Moderate 7 of 52 days19941995: Good 47 of 51 days1995: Moderate 4 of 51 days1996: Good 57 of 59 days1996: Moderate 2 of 59 days19961997: Good 61 of 63 days1997: Moderate 2 of 63 days1998: Good 111 of 115 days1998: Moderate 4 of 115 days19981999: Good 119 of 121 days1999: Moderate 2 of 121 days2000: Good 113 of 120 days2000: Moderate 6 of 120 days2000: Unhealthy for Sensitive Groups 1 of 120 days20002001: Good 112 of 122 days2001: Moderate 10 of 122 days2002: Good 136 of 143 days2002: Moderate 7 of 143 days20022003: Good 321 of 332 days2003: Moderate 11 of 332 days2004: Good 213 of 221 days2004: Moderate 8 of 221 days20042005: Good 248 of 268 days2005: Moderate 19 of 268 days2005: Unhealthy for Sensitive Groups 1 of 268 days2006: Good 298 of 307 days2006: Moderate 9 of 307 days20062007: Good 317 of 326 days2007: Moderate 9 of 326 days2008: Good 321 of 327 days2008: Moderate 6 of 327 days20082009: Good 318 of 323 days2009: Moderate 5 of 323 days2010: Good 311 of 312 days2010: Moderate 1 of 312 days20102011: Good 314 of 318 days2011: Moderate 4 of 318 days2012: Good 119 of 123 days2012: Moderate 4 of 123 days2012
  • 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 year0501001992: 90th percentile AQI 321993: 90th percentile AQI 541994: 90th percentile AQI 541995: 90th percentile AQI 441996: 90th percentile AQI 371997: 90th percentile AQI 291998: 90th percentile AQI 321999: 90th percentile AQI 362000: 90th percentile AQI 432001: 90th percentile AQI 442002: 90th percentile AQI 402003: 90th percentile AQI 282004: 90th percentile AQI 272005: 90th percentile AQI 462006: 90th percentile AQI 312007: 90th percentile AQI 292008: 90th percentile AQI 272009: 90th percentile AQI 322010: 90th percentile AQI 252011: 90th percentile AQI 272012: 90th percentile AQI 311992: Median AQI 181993: Median AQI 151994: Median AQI 211995: Median AQI 171996: Median AQI 181997: Median AQI 171998: Median AQI 181999: Median AQI 172000: Median AQI 172001: Median AQI 172002: Median AQI 172003: Median AQI 132004: Median AQI 132005: Median AQI 142006: Median AQI 132007: Median AQI 132008: Median AQI 112009: Median AQI 132010: Median AQI 122011: Median AQI 122012: Median AQI 1219921994199619982000200220042006200820102012
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2012

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
Coarse particles (PM10)123100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
201212311940000123164PM10
201131831440000122766PM10
201031231110000122563PM10
200932331850000133274PM10
200832732160000112775PM10
200732631790000132964PM10
200630729890000133166PM10
20052682481910001446108PM10
200422121380000132764PM10
2003332321110000132864PM10
200214313670000174072PM10
2001122112100000174477PM10
2000120113610001743114PM10
199912111920000173654PM10
199811511140000183286PM10
1997636120000172971PM10
1996595720000183762PM10
1995514740000174472PM10
1994524570000215486PM10
1993564970000155488PM10
1992292810000183261PM10

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.

All monitored counties in Colorado

Source: U.S. EPA AirData, “Annual AQI by County” files for 1992–2012 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem