EnviroNearby

Alamosa County, Colorado air quality history

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

92%
Good days in 2025
25
Median daily AQI, 2025
0
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 Alamosa, Colorado on 365 days. 334 of those days (92%) were in the Good range, and the median daily AQI was 25. That median is lower than the typical monitored county in Colorado (median 46 across 27 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 314 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 91% in 1988–1990 versus 89% in 2023–2025.

Years with fewer than 120 monitored days (2019, 2020, 2022) 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 247 of 257 days1988: Moderate 10 of 257 days19881989: Good 324 of 357 days1989: Moderate 32 of 357 days1989: Unhealthy for Sensitive Groups 1 of 357 days1990: Good 318 of 365 days1990: Moderate 47 of 365 days1991: Good 289 of 360 days1991: Moderate 69 of 360 days1991: Unhealthy for Sensitive Groups 1 of 360 days1991: Very Unhealthy 1 of 360 days1992: Good 323 of 356 days1992: Moderate 33 of 356 days1993: Good 343 of 351 days1993: Moderate 8 of 351 days19931994: Good 339 of 351 days1994: Moderate 12 of 351 days1995: Good 345 of 356 days1995: Moderate 10 of 356 days1995: Unhealthy for Sensitive Groups 1 of 356 days1996: Good 319 of 325 days1996: Moderate 6 of 325 days1997: Good 331 of 339 days1997: Moderate 8 of 339 days1998: Good 328 of 341 days1998: Moderate 13 of 341 days19981999: Good 295 of 315 days1999: Moderate 18 of 315 days1999: Unhealthy for Sensitive Groups 1 of 315 days1999: Unhealthy 1 of 315 days2000: Good 267 of 282 days2000: Moderate 13 of 282 days2000: Unhealthy for Sensitive Groups 2 of 282 days2001: Good 318 of 328 days2001: Moderate 10 of 328 days2002: Good 316 of 348 days2002: Moderate 28 of 348 days2002: Unhealthy for Sensitive Groups 4 of 348 days2003: Good 338 of 364 days2003: Moderate 26 of 364 days20032004: Good 347 of 362 days2004: Moderate 15 of 362 days2005: Good 348 of 364 days2005: Moderate 16 of 364 days2006: Good 344 of 362 days2006: Moderate 13 of 362 days2006: Unhealthy for Sensitive Groups 4 of 362 days2006: Very Unhealthy 1 of 362 days2007: Good 350 of 364 days2007: Moderate 13 of 364 days2007: Hazardous 1 of 364 days2008: Good 342 of 361 days2008: Moderate 17 of 361 days2008: Unhealthy for Sensitive Groups 2 of 361 days20082009: Good 346 of 360 days2009: Moderate 12 of 360 days2009: Unhealthy for Sensitive Groups 2 of 360 days2010: Good 337 of 355 days2010: Moderate 14 of 355 days2010: Unhealthy for Sensitive Groups 2 of 355 days2010: Unhealthy 2 of 355 days2011: Good 311 of 360 days2011: Moderate 47 of 360 days2011: Very Unhealthy 1 of 360 days2011: Hazardous 1 of 360 days2012: Good 330 of 366 days2012: Moderate 30 of 366 days2012: Unhealthy for Sensitive Groups 4 of 366 days2012: Unhealthy 1 of 366 days2012: Very Unhealthy 1 of 366 days2013: Good 346 of 364 days2013: Moderate 13 of 364 days2013: Unhealthy for Sensitive Groups 5 of 364 days20132014: Good 345 of 365 days2014: Moderate 18 of 365 days2014: Unhealthy for Sensitive Groups 2 of 365 days2015: Good 356 of 364 days2015: Moderate 8 of 364 days2016: Good 354 of 360 days2016: Moderate 4 of 360 days2016: Unhealthy for Sensitive Groups 1 of 360 days2016: Very Unhealthy 1 of 360 days2017: Good 351 of 354 days2017: Moderate 3 of 354 days2018: Good 348 of 360 days2018: Moderate 11 of 360 days2018: Very Unhealthy 1 of 360 days20182019: Good 107 of 107 days2020: Good 112 of 119 days2020: Moderate 7 of 119 days2021: Good 114 of 120 days2021: Moderate 5 of 120 days2021: Unhealthy for Sensitive Groups 1 of 120 days2022: Good 107 of 116 days2022: Moderate 8 of 116 days2022: Unhealthy for Sensitive Groups 1 of 116 days2023: Good 142 of 165 days2023: Moderate 23 of 165 days20232024: Good 325 of 365 days2024: Moderate 40 of 365 days2025: Good 334 of 365 days2025: Moderate 31 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 year0501001988: 90th percentile AQI 481989: 90th percentile AQI 501990: 90th percentile AQI 521991: 90th percentile AQI 581992: 90th percentile AQI 501993: 90th percentile AQI 381994: 90th percentile AQI 361995: 90th percentile AQI 351996: 90th percentile AQI 351997: 90th percentile AQI 311998: 90th percentile AQI 361999: 90th percentile AQI 402000: 90th percentile AQI 412001: 90th percentile AQI 392002: 90th percentile AQI 482003: 90th percentile AQI 422004: 90th percentile AQI 352005: 90th percentile AQI 392006: 90th percentile AQI 382007: 90th percentile AQI 422008: 90th percentile AQI 382009: 90th percentile AQI 402010: 90th percentile AQI 412011: 90th percentile AQI 552012: 90th percentile AQI 502013: 90th percentile AQI 422014: 90th percentile AQI 372015: 90th percentile AQI 322016: 90th percentile AQI 312017: 90th percentile AQI 322018: 90th percentile AQI 372019: 90th percentile AQI 232020: 90th percentile AQI 402021: 90th percentile AQI 352022: 90th percentile AQI 442023: 90th percentile AQI 532024: 90th percentile AQI 512025: 90th percentile AQI 491988: Median AQI 401989: Median AQI 421990: Median AQI 421991: Median AQI 421992: Median AQI 231993: Median AQI 211994: Median AQI 201995: Median AQI 191996: Median AQI 181997: Median AQI 191998: Median AQI 191999: Median AQI 182000: Median AQI 192001: Median AQI 192002: Median AQI 242003: Median AQI 242004: Median AQI 212005: Median AQI 192006: Median AQI 202007: Median AQI 232008: Median AQI 212009: Median AQI 192010: Median AQI 202011: Median AQI 262012: Median AQI 242013: Median AQI 202014: Median AQI 192015: Median AQI 182016: Median AQI 182017: Median AQI 192018: Median AQI 192019: Median AQI 122020: Median AQI 142021: Median AQI 122022: Median AQI 112023: Median AQI 222024: Median AQI 262025: Median AQI 25198819931998200320082013201820232025
  • 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
Fine particles (PM2.5)31486%
Coarse particles (PM10)5114%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025365334310000254976PM2.5
2024365325400000265198PM2.5
2023165142230000225370PM2.5
2022116107810001144134PM2.5
2021120114510001235109PM2.5
202011911270000144065PM2.5
201910710700000122328PM2.5
20183603481100101937235PM10
201735435130000193253PM10
2016360354410101831271PM10
201536435680000183287PM10
20143653451820001937124PM10
20133643461350002042146PM10
20123663303041102450250PM10
20113603114700112655534PM10
20103553371422002041166PM10
20093603461220001940127PM10
20083613421720002138102PM10
20073643501300012342378PM10
20063623441340102038300PM10
2005364348160000193994PM10
2004362347150000213595PM10
2003364338260000244298PM10
20023483162840002448131PM10
2001328318100000193977PM10
20002822671320001941142PM10
19993152951811001840155PM10
1998341328130000193674PM10
199733933180000193195PM10
199632531960000183587PM10
19953563451010001935102PM10
1994351339120000203689PM10
199335134380000213873PM10
1992356323330000235076PM10
19913602896910104258283Ozone
1990365318470000425287Ozone
19893573243210004250125Ozone
1988257247100000404884Ozone

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 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