EnviroNearby

Custer County, South Dakota air quality history

Daily Air Quality Index summaries from EPA monitors in Custer, South Dakota, 2000–2025.

74%
Good days in 2025
45
Median daily AQI, 2025
0
Days above 100 in 2025
360
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Custer, South Dakota on 360 days. 265 of those days (74%) were in the Good range, and the median daily AQI was 45. That median is higher than the typical monitored county in South Dakota (median 35.5 across 10 counties), and higher than the typical monitored U.S. county (40). The main pollutant was ozone on 229 days. Across the years with fuller monitoring, the share of Good days fell: an average of 91% in 2002–2005 versus 78% in 2023–2025.

Years with fewer than 120 monitored days (2000, 2001, 2003) 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%2000: Good 88 of 94 days2000: Moderate 6 of 94 days20002001: Good 95 of 96 days2001: Moderate 1 of 96 days2002: Good 114 of 120 days2002: Moderate 6 of 120 days20022003: Good 111 of 118 days2003: Moderate 7 of 118 days2004: Good 121 of 122 days2004: Moderate 1 of 122 days20042005: Good 286 of 364 days2005: Moderate 75 of 364 days2005: Unhealthy for Sensitive Groups 3 of 364 days2006: Good 250 of 365 days2006: Moderate 109 of 365 days2006: Unhealthy for Sensitive Groups 6 of 365 days20062007: Good 285 of 365 days2007: Moderate 78 of 365 days2007: Unhealthy for Sensitive Groups 2 of 365 days2008: Good 326 of 366 days2008: Moderate 39 of 366 days2008: Unhealthy for Sensitive Groups 1 of 366 days20082009: Good 327 of 365 days2009: Moderate 34 of 365 days2009: Unhealthy for Sensitive Groups 1 of 365 days2009: Unhealthy 2 of 365 days2009: Hazardous 1 of 365 days2010: Good 328 of 364 days2010: Moderate 34 of 364 days2010: Unhealthy for Sensitive Groups 1 of 364 days2010: Unhealthy 1 of 364 days20102011: Good 334 of 365 days2011: Moderate 31 of 365 days2012: Good 264 of 364 days2012: Moderate 97 of 364 days2012: Unhealthy for Sensitive Groups 3 of 364 days20122013: Good 325 of 365 days2013: Moderate 40 of 365 days2014: Good 359 of 365 days2014: Moderate 6 of 365 days20142015: Good 326 of 365 days2015: Moderate 37 of 365 days2015: Unhealthy for Sensitive Groups 2 of 365 days2016: Good 340 of 366 days2016: Moderate 26 of 366 days20162017: Good 299 of 363 days2017: Moderate 61 of 363 days2017: Unhealthy for Sensitive Groups 2 of 363 days2017: Unhealthy 1 of 363 days2018: Good 311 of 365 days2018: Moderate 54 of 365 days20182019: Good 352 of 362 days2019: Moderate 10 of 362 days2020: Good 323 of 366 days2020: Moderate 41 of 366 days2020: Unhealthy for Sensitive Groups 2 of 366 days20202021: Good 302 of 364 days2021: Moderate 59 of 364 days2021: Unhealthy for Sensitive Groups 2 of 364 days2021: Very Unhealthy 1 of 364 days2022: Good 298 of 362 days2022: Moderate 62 of 362 days2022: Unhealthy for Sensitive Groups 2 of 362 days20222023: Good 308 of 365 days2023: Moderate 48 of 365 days2023: Unhealthy for Sensitive Groups 4 of 365 days2023: Unhealthy 5 of 365 days2024: Good 276 of 366 days2024: Moderate 81 of 366 days2024: Unhealthy for Sensitive Groups 9 of 366 days20242025: Good 265 of 360 days2025: Moderate 95 of 360 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 year0501002000: 90th percentile AQI 362001: 90th percentile AQI 352002: 90th percentile AQI 382003: 90th percentile AQI 392004: 90th percentile AQI 292005: 90th percentile AQI 642006: 90th percentile AQI 802007: 90th percentile AQI 672008: 90th percentile AQI 512009: 90th percentile AQI 512010: 90th percentile AQI 502011: 90th percentile AQI 502012: 90th percentile AQI 672013: 90th percentile AQI 512014: 90th percentile AQI 472015: 90th percentile AQI 512016: 90th percentile AQI 492017: 90th percentile AQI 582018: 90th percentile AQI 542019: 90th percentile AQI 482020: 90th percentile AQI 542021: 90th percentile AQI 602022: 90th percentile AQI 582023: 90th percentile AQI 582024: 90th percentile AQI 642025: 90th percentile AQI 582000: Median AQI 142001: Median AQI 142002: Median AQI 152003: Median AQI 152004: Median AQI 172005: Median AQI 432006: Median AQI 442007: Median AQI 412008: Median AQI 402009: Median AQI 382010: Median AQI 402011: Median AQI 402012: Median AQI 432013: Median AQI 412014: Median AQI 392015: Median AQI 402016: Median AQI 392017: Median AQI 422018: Median AQI 412019: Median AQI 402020: Median AQI 412021: Median AQI 392022: Median AQI 412023: Median AQI 432024: Median AQI 442025: Median AQI 4520002002200420062008201020122014201620182020202220242025
  • 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
Ozone22964%
Fine particles (PM2.5)13136%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025360265950000455887Ozone
20243662768190004464126Ozone
20233653084845004358167Ozone
20223622986220004158130Ozone
20213643025920103960209Ozone
20203663234120004154119Ozone
2019362352100000404884Ozone
2018365311540000415489Ozone
20173632996121004258162Ozone
2016366340260000394997Ozone
20153653263720004051133Ozone
2014365359600003947100Ozone
2013365325400000415174Ozone
20123642649730004367112Ozone
2011365334310000405067Ozone
20103643283411004050193Ozone
20093653273412013851457Ozone
20083663263910004051116Ozone
20073652857820004167115Ozone
200636525010960004480126Ozone
20053642867530004364122Ozone
200412212110000172952PM2.5
200311811170000153958PM2.5
200212011460000153868PM2.5
2001969510000143555PM2.5
2000948860000143660PM2.5

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 South Dakota with a similar median AQI in 2025

All monitored counties in South Dakota

Source: U.S. EPA AirData, “Annual AQI by County” files for 2000–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem