Custer, South Dakota Air Quality Today
AirHistory tracks long-run EPA monitoring rather than live readings, so for the live number check AirNow.gov below. As a baseline, Custer, South Dakota's most recent EPA year (2023) posted a median AQI of 43 (Good) against a 5-year median of 41 and an overall Grade of C. The dominant pollutant is Ground-Level Ozone, which tells you which days are most likely to spike.
Check Today's Live AQI in Custer, South Dakota
AirHistory is built on 10 years of EPA Air Quality System records, so it shows you what air quality in Custer, South Dakota typically looks like — not the live reading for this exact hour. For today's real-time AQI, check AirNow.gov (the EPA's official live index) or the AirNow Fire and Smoke Map during wildfire season.
That said, the history is the best predictor of a normal day. In 2023, Custer, South Dakota posted a median AQI of 43 (Good), with 308 "Good" days and 9 days that crossed into "Unhealthy for Sensitive Groups" or worse. The dominant pollutant, Ground-Level Ozone, is the one most likely to push today's number up — Ground-level ozone forms when sunlight reacts with vehicle exhaust and industrial emissions. It is worst on hot, sunny, stagnant summer days. Ozone irritates the lungs, triggers asthma attacks, and reduces lung function — even healthy adults can feel chest tightness and shortness of breath after exercising in elevated ozone.
Custer, South Dakota Air Quality Snapshot
| Air Quality Grade | C62/100 |
| 5-Year Median AQI | 41 (Good) |
| Most Recent Median AQI (2023) | 43 (Good) |
| Dominant Pollutant | Ground-Level Ozone |
| 10-Year Trend | Stable (+0.24 AQI/yr) |
| Unhealthy Days (last 5 yr) | 16 |
| National Rank (cleanest = #1) | #538 of 1,020 (53th most polluted percentile) |
| South Dakota Rank | #10 of 10 |
What Does the C Grade Mean?
Custer, South Dakota earns a C — air quality is fair, but not great. With a 5-year median AQI of 41, the city sees a meaningful number of "Moderate" days each year, when the EPA flags air as a concern for unusually sensitive people.
Custer, South Dakota's 5-year median AQI of 41 is right around the national average of 41 across the 1,020 monitored U.S. cities tracked here. Within South Dakota, Custer, South Dakota runs more polluted than the state average of 36 — local sources or geography are concentrating pollution above the state's typical reading.
For context within South Dakota: Hughes, South Dakota currently holds the state's cleanest grade (A, AQI 13), while Codington, South Dakota sits at the bottom (D, AQI 40).
What's in Custer, South Dakota's Air?
The dominant pollutant in Custer, South Dakota is Ground-Level Ozone. Ground-level ozone forms when sunlight reacts with vehicle exhaust and industrial emissions. It is worst on hot, sunny, stagnant summer days. Ozone irritates the lungs, triggers asthma attacks, and reduces lung function — even healthy adults can feel chest tightness and shortness of breath after exercising in elevated ozone.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Ground-Level Ozone | 303 | 83% |
| Fine Particulate Matter (PM2.5) | 59 | 16% |
| Coarse Particulate Matter (PM10) | 3 | 1% |
Is the Air Getting Better or Worse?
Air quality in Custer, South Dakota has held roughly steady over the past decade, with year-to-year shifts in median AQI of less than half a point. That stability makes the city's long-run grade a reliable signal of what residents can expect day-to-day.
In 2014, Custer, South Dakota posted a median AQI of 39. By 2023 that figure was 43 — a rise of 4 AQI points dirtier across 10 years of EPA records.
Year-by-Year AQI in Custer, South Dakota
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 39 | 359 | 0 | Ozone |
| 2015 | 40 | 326 | 2 | Ozone |
| 2016 | 39 | 340 | 0 | Ozone |
| 2017 | 42 | 299 | 3 | Ozone |
| 2018 | 41 | 311 | 0 | Ozone |
| 2019 | 40 | 352 | 0 | Ozone |
| 2020 | 41 | 323 | 2 | Ozone |
| 2021 | 39 | 302 | 3 | Ozone |
| 2022 | 41 | 298 | 2 | Ozone |
| 2023 | 43 | 308 | 9 | Ozone |
Health Context for Custer, South Dakota
Across the past five years, this area has logged just 16 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 3 days per year, or roughly one every other month. That is a low count by national standards.
Healthy adults can continue normal outdoor activity in most weather, but should pay attention to AQI alerts during the worst pollution windows. People with asthma, heart disease, or pregnancy should reduce prolonged or intense outdoor exertion on flagged days, and consider running an indoor HEPA air cleaner during peak season. Because ozone peaks in the afternoon on hot sunny days, plan outdoor exercise for early morning or after sunset on bad-air days.
How This Grade Is Calculated
The AirHistory Air Quality Grade combines four signals: the 5-year median AQI (40% of the score), the 10-year trend direction (30%), the count of unhealthy days per year (20%), and the dominant pollutant type (10%). All four come directly from the EPA Air Quality System (AQS), which aggregates readings from federally certified monitors. Read the full methodology.
More about Custer, South Dakota
Custer, South Dakota has an Air Quality Grade of C (fair) with a 5-year median AQI of 41. The dominant pollutant is Ground-Level Ozone, and air quality has been stable over the past decade.
The data source behind this answer is the EPA Air Quality System (AQS). Every figure on the page traces back to that source; the methodology page describes the inputs and the refresh cadence in full detail.
A practical caveat: the headline answer above reflects the most recent the EPA Air Quality System (AQS) vintage; underlying data is often revised for months after first publication, and the right reference for any specific decision is whichever vintage is current at the time of the decision. The as-of date is stamped on every page.
Source: EPA Outdoor Air Quality Data, 2026.