EnviroNearby

San Juan County, Colorado air quality history

Daily Air Quality Index summaries from EPA monitors in San Juan, Colorado, 1988–2025.

99%
Good days in 2024
9
Median daily AQI, 2024
0
Days above 100 in 2024
121
Days with an AQI in 2024 (of 366)

In 2024, EPA reported a daily Air Quality Index (AQI) for San Juan, Colorado on 121 days. 120 of those days (99%) were in the Good range, and the median daily AQI was 9. That median is lower than the typical monitored county in Colorado (median 47.5 across 30 counties), and lower than the typical monitored U.S. county (41). The main pollutant was fine particles (PM2.5) on 121 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 99% in 2005–2009 versus 100% in 2016–2024.

EPA did not report an AQI for every day of 2024 here (121 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.

Years with fewer than 120 monitored days (2018, 2019, 2020, 2021, 2022, 2025…) 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%1988: Good 74 of 75 days1988: Moderate 1 of 75 days19881989: Good 90 of 90 days1990: Good 85 of 89 days1990: Moderate 4 of 89 days1991: Good 96 of 97 days1991: Moderate 1 of 97 days1992: Good 92 of 92 days1993: Good 94 of 94 days19931994: Good 96 of 96 days1995: Good 100 of 100 days1996: Good 85 of 87 days1996: Moderate 2 of 87 days1997: Good 99 of 99 days1998: Good 99 of 99 days19981999: Good 96 of 97 days1999: Moderate 1 of 97 days2000: Good 83 of 84 days2000: Moderate 1 of 84 days2001: Good 117 of 117 days2002: Good 101 of 101 days2003: Good 116 of 117 days2003: Moderate 1 of 117 days20032004: Good 118 of 118 days2005: Good 119 of 120 days2005: Moderate 1 of 120 days2006: Good 122 of 122 days2007: Good 117 of 118 days2007: Moderate 1 of 118 days2008: Good 114 of 117 days2008: Moderate 3 of 117 days20082009: Good 119 of 122 days2009: Moderate 3 of 122 days2010: Good 116 of 119 days2010: Moderate 3 of 119 days2011: Good 121 of 121 days2012: Good 116 of 119 days2012: Moderate 3 of 119 days2013: Good 117 of 118 days2013: Moderate 1 of 118 days20132014: Good 118 of 118 days2015: Good 120 of 121 days2015: Moderate 1 of 121 days2016: Good 121 of 121 days2017: Good 119 of 119 days2018: Good 109 of 118 days2018: Moderate 9 of 118 days20182019: Good 116 of 116 days2020: Good 115 of 119 days2020: Moderate 4 of 119 days2021: Good 114 of 119 days2021: Moderate 5 of 119 days2022: Good 115 of 119 days2022: Moderate 4 of 119 days2023: Good 120 of 120 days20232024: Good 120 of 121 days2024: Moderate 1 of 121 days2025: Good 91 of 92 days2025: Moderate 1 of 92 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 year0501001988: 90th percentile AQI 281989: 90th percentile AQI 301990: 90th percentile AQI 381991: 90th percentile AQI 281992: 90th percentile AQI 221993: 90th percentile AQI 251994: 90th percentile AQI 291995: 90th percentile AQI 261996: 90th percentile AQI 251997: 90th percentile AQI 241998: 90th percentile AQI 261999: 90th percentile AQI 272000: 90th percentile AQI 272001: 90th percentile AQI 232002: 90th percentile AQI 252003: 90th percentile AQI 282004: 90th percentile AQI 192005: 90th percentile AQI 252006: 90th percentile AQI 212007: 90th percentile AQI 252008: 90th percentile AQI 242009: 90th percentile AQI 252010: 90th percentile AQI 222011: 90th percentile AQI 202012: 90th percentile AQI 282013: 90th percentile AQI 232014: 90th percentile AQI 222015: 90th percentile AQI 202016: 90th percentile AQI 182017: 90th percentile AQI 212018: 90th percentile AQI 332019: 90th percentile AQI 192020: 90th percentile AQI 312021: 90th percentile AQI 332022: 90th percentile AQI 262023: 90th percentile AQI 202024: 90th percentile AQI 192025: 90th percentile AQI 291988: Median AQI 161989: Median AQI 161990: Median AQI 161991: Median AQI 131992: Median AQI 151993: Median AQI 151994: Median AQI 161995: Median AQI 131996: Median AQI 121997: Median AQI 141998: Median AQI 131999: Median AQI 162000: Median AQI 132001: Median AQI 122002: Median AQI 112003: Median AQI 122004: Median AQI 112005: Median AQI 102006: Median AQI 112007: Median AQI 122008: Median AQI 112009: Median AQI 122010: Median AQI 112011: Median AQI 112012: Median AQI 132013: Median AQI 122014: Median AQI 102015: Median AQI 82016: Median AQI 82017: Median AQI 92018: Median AQI 102019: Median AQI 92020: Median AQI 92021: Median AQI 92022: Median AQI 102023: Median AQI 92024: Median AQI 92025: Median AQI 12198819931998200320082013201820232025
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2024

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
Fine particles (PM2.5)121100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025929110000122957PM2.5
20241211201000091951PM2.5
20231201200000092050PM2.5
202211911540000102675PM2.5
20211191145000093379PM2.5
20201191154000093173PM2.5
20191161160000091932PM2.5
2018118109900001033100PM2.5
20171191190000092149PM2.5
20161211210000081831PM2.5
20151211201000082055PM2.5
201411811800000102237PM2.5
201311811710000122398PM2.5
201211911630000132882PM2.5
201112112100000112048PM2.5
201011911630000112286PM2.5
200912211930000122561PM2.5
200811711430000112462PM2.5
200711811710000122562PM2.5
200612212200000112139PM2.5
200512011910000102558PM2.5
200411811800000111928PM2.5
200311711610000122851PM2.5
200210110100000112541PM2.5
200111711700000122339PM2.5
2000848310000132752PM2.5
1999979610000162771PM2.5
1998999900000132644PM2.5
1997999900000142443PM2.5
1996878520000122554PM2.5
199510010000000132646PM2.5
1994969600000162947PM2.5
1993949400000152538PM2.5
1992929200000152234PM2.5
1991979610000132857PM2.5
1990898540000163868PM2.5
1989909000000163047PM2.5
1988757410000162855PM2.5

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 2024

All monitored counties in Colorado

Source: U.S. EPA AirData, “Annual AQI by County” files for 1988–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem