EnviroNearby

Sweetwater County, Wyoming air quality history

Daily Air Quality Index summaries from EPA monitors in Sweetwater, Wyoming, 1985–2025.

73%
Good days in 2025
44
Median daily AQI, 2025
8
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 Sweetwater, Wyoming on 365 days. 266 of those days (73%) were in the Good range, and the median daily AQI was 44. That median is higher than the typical monitored county in Wyoming (median 41 across 17 counties), and higher than the typical monitored U.S. county (40). The main pollutant was ozone on 304 days. Across the years with fuller monitoring, the share of Good days fell: an average of 91% in 1991–1993 versus 70% in 2023–2025.

Years with fewer than 120 monitored days (1987, 1989, 1990, 1997, 1998, 1999…) 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%1985: Good 48 of 50 days1985: Moderate 2 of 50 days19851986: Good 46 of 50 days1986: Moderate 4 of 50 days1987: Good 29 of 34 days1987: Moderate 5 of 34 days1989: Good 55 of 61 days1989: Moderate 6 of 61 days1990: Good 53 of 62 days1990: Moderate 9 of 62 days1991: Good 182 of 201 days1991: Moderate 18 of 201 days1991: Unhealthy for Sensitive Groups 1 of 201 days19911992: Good 219 of 248 days1992: Moderate 27 of 248 days1992: Unhealthy 2 of 248 days1993: Good 247 of 262 days1993: Moderate 14 of 262 days1993: Unhealthy for Sensitive Groups 1 of 262 days1994: Good 267 of 278 days1994: Moderate 11 of 278 days1995: Good 282 of 298 days1995: Moderate 16 of 298 days1996: Good 122 of 131 days1996: Moderate 9 of 131 days19961997: Good 53 of 62 days1997: Moderate 9 of 62 days1998: Good 56 of 62 days1998: Moderate 6 of 62 days1999: Good 58 of 63 days1999: Moderate 5 of 63 days2000: Good 265 of 288 days2000: Moderate 22 of 288 days2000: Unhealthy 1 of 288 days2001: Good 315 of 365 days2001: Moderate 47 of 365 days2001: Unhealthy for Sensitive Groups 2 of 365 days2001: Very Unhealthy 1 of 365 days20012002: Good 292 of 365 days2002: Moderate 66 of 365 days2002: Unhealthy for Sensitive Groups 4 of 365 days2002: Unhealthy 2 of 365 days2002: Very Unhealthy 1 of 365 days2003: Good 285 of 365 days2003: Moderate 71 of 365 days2003: Unhealthy for Sensitive Groups 9 of 365 days2004: Good 323 of 366 days2004: Moderate 39 of 366 days2004: Unhealthy for Sensitive Groups 1 of 366 days2004: Unhealthy 2 of 366 days2004: Hazardous 1 of 366 days2005: Good 336 of 365 days2005: Moderate 27 of 365 days2005: Unhealthy for Sensitive Groups 1 of 365 days2005: Unhealthy 1 of 365 days2006: Good 261 of 365 days2006: Moderate 99 of 365 days2006: Unhealthy for Sensitive Groups 4 of 365 days2006: Hazardous 1 of 365 days20062007: Good 218 of 365 days2007: Moderate 144 of 365 days2007: Unhealthy for Sensitive Groups 3 of 365 days2008: Good 230 of 366 days2008: Moderate 129 of 366 days2008: Unhealthy for Sensitive Groups 6 of 366 days2008: Unhealthy 1 of 366 days2009: Good 273 of 365 days2009: Moderate 90 of 365 days2009: Unhealthy for Sensitive Groups 1 of 365 days2009: Unhealthy 1 of 365 days2010: Good 245 of 365 days2010: Moderate 117 of 365 days2010: Unhealthy for Sensitive Groups 3 of 365 days2011: Good 229 of 365 days2011: Moderate 131 of 365 days2011: Unhealthy for Sensitive Groups 5 of 365 days20112012: Good 210 of 366 days2012: Moderate 148 of 366 days2012: Unhealthy for Sensitive Groups 7 of 366 days2012: Very Unhealthy 1 of 366 days2013: Good 251 of 365 days2013: Moderate 111 of 365 days2013: Unhealthy for Sensitive Groups 2 of 365 days2013: Hazardous 1 of 365 days2014: Good 247 of 365 days2014: Moderate 110 of 365 days2014: Unhealthy for Sensitive Groups 6 of 365 days2014: Unhealthy 2 of 365 days2015: Good 256 of 365 days2015: Moderate 105 of 365 days2015: Unhealthy for Sensitive Groups 4 of 365 days2016: Good 303 of 366 days2016: Moderate 63 of 366 days20162017: Good 259 of 365 days2017: Moderate 101 of 365 days2017: Unhealthy for Sensitive Groups 2 of 365 days2017: Unhealthy 2 of 365 days2017: Very Unhealthy 1 of 365 days2018: Good 210 of 365 days2018: Moderate 147 of 365 days2018: Unhealthy for Sensitive Groups 7 of 365 days2018: Unhealthy 1 of 365 days2019: Good 258 of 365 days2019: Moderate 104 of 365 days2019: Unhealthy for Sensitive Groups 3 of 365 days2020: Good 235 of 366 days2020: Moderate 119 of 366 days2020: Unhealthy for Sensitive Groups 7 of 366 days2020: Unhealthy 4 of 366 days2020: Hazardous 1 of 366 days2021: Good 238 of 365 days2021: Moderate 117 of 365 days2021: Unhealthy for Sensitive Groups 9 of 365 days2021: Unhealthy 1 of 365 days20212022: Good 285 of 365 days2022: Moderate 78 of 365 days2022: Unhealthy for Sensitive Groups 1 of 365 days2022: Unhealthy 1 of 365 days2023: Good 253 of 365 days2023: Moderate 103 of 365 days2023: Unhealthy for Sensitive Groups 8 of 365 days2023: Very Unhealthy 1 of 365 days2024: Good 247 of 366 days2024: Moderate 109 of 366 days2024: Unhealthy for Sensitive Groups 10 of 366 days2025: Good 266 of 365 days2025: Moderate 91 of 365 days2025: Unhealthy for Sensitive Groups 8 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 year0501001985: 90th percentile AQI 491986: 90th percentile AQI 491987: 90th percentile AQI 521989: 90th percentile AQI 501990: 90th percentile AQI 541991: 90th percentile AQI 501992: 90th percentile AQI 531993: 90th percentile AQI 401994: 90th percentile AQI 351995: 90th percentile AQI 391996: 90th percentile AQI 411997: 90th percentile AQI 541998: 90th percentile AQI 451999: 90th percentile AQI 482000: 90th percentile AQI 482001: 90th percentile AQI 542002: 90th percentile AQI 652003: 90th percentile AQI 592004: 90th percentile AQI 532005: 90th percentile AQI 462006: 90th percentile AQI 712007: 90th percentile AQI 742008: 90th percentile AQI 742009: 90th percentile AQI 602010: 90th percentile AQI 662011: 90th percentile AQI 712012: 90th percentile AQI 742013: 90th percentile AQI 672014: 90th percentile AQI 712015: 90th percentile AQI 712016: 90th percentile AQI 582017: 90th percentile AQI 672018: 90th percentile AQI 742019: 90th percentile AQI 642020: 90th percentile AQI 762021: 90th percentile AQI 832022: 90th percentile AQI 612023: 90th percentile AQI 712024: 90th percentile AQI 752025: 90th percentile AQI 641985: Median AQI 281986: Median AQI 231987: Median AQI 291989: Median AQI 301990: Median AQI 301991: Median AQI 241992: Median AQI 261993: Median AQI 141994: Median AQI 151995: Median AQI 191996: Median AQI 181997: Median AQI 291998: Median AQI 251999: Median AQI 262000: Median AQI 242001: Median AQI 262002: Median AQI 252003: Median AQI 282004: Median AQI 202005: Median AQI 202006: Median AQI 422007: Median AQI 462008: Median AQI 472009: Median AQI 452010: Median AQI 452011: Median AQI 482012: Median AQI 472013: Median AQI 452014: Median AQI 462015: Median AQI 452016: Median AQI 442017: Median AQI 462018: Median AQI 482019: Median AQI 462020: Median AQI 462021: Median AQI 452022: Median AQI 442023: Median AQI 472024: Median AQI 452025: Median AQI 44198519911996200120062011201620212025
  • 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
Ozone30483%
Coarse particles (PM10)4412%
Fine particles (PM2.5)175%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253652669180004464118Ozone
2024366247109100004575137Ozone
202336525310380104771211Ozone
20223652857811004461157Ozone
202136523811791004583195Ozone
2020366235119740146761334Ozone
201936525810430004664133Ozone
201836521014771004874163Ozone
201736525910122104667264Ozone
20163663036300004458100Ozone
201536525610540004571119Ozone
201436524711062004671197Ozone
201336525111120014567309Ozone
201236621014870104774284Ozone
201136522913150004871108Ozone
201036524511730004566112Ozone
20093652739011004560163Ozone
200836623012961004774172Ozone
200736521814430004674137Ozone
20063652619940014271339Ozone
20053653362711002046193PM10
20043663233912012053402PM10
20033652857190002859131PM10
20023652926642102565273PM10
20013653154720102654227PM10
20002882652201002448172PM10
1999635850000264863PM10
1998625660000254570PM10
1997625390000295462PM10
199613112290000184169PM10
1995298282160000193999PM10
1994278267110000153583PM10
19932622471410001440125PM10
19922482192702002653163PM10
19912011821810002450102PM10
1990625390000305472PM10
1989615560000305064PM10
1987342950000295283PM10
1986504640000234960PM10
1985504820000284954PM10

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 Wyoming with a similar median AQI in 2025

All monitored counties in Wyoming

Source: U.S. EPA AirData, “Annual AQI by County” files for 1985–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem