What Is the Air Quality in Sangamon, Illinois?
Sangamon, Illinois has an Air Quality Grade of D (poor) with a 5-year median AQI of 46. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been worsening over the past decade.
Sangamon, Illinois Air Quality Snapshot
| Air Quality Grade | D48/100 |
| 5-Year Median AQI | 46 (Good) |
| Most Recent Median AQI (2023) | 51 (Moderate) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Worsening (+1.61 AQI/yr) |
| Unhealthy Days (last 5 yr) | 24 |
| National Rank (cleanest = #1) | #795 of 1,020 (78th most polluted percentile) |
| Illinois Rank | #11 of 23 |
What Does the D Grade Mean?
Sangamon, Illinois earns a D — air quality falls below the U.S. average, with a 5-year median AQI of 46. Residents with asthma, COPD, heart disease, or young children should watch daily AQI forecasts and limit outdoor exertion when alerts go out.
Sangamon, Illinois's 5-year median AQI of 46 is 5 points above the national average of 41 — meaningfully more polluted than the typical U.S. metro tracked here. Within Illinois, Sangamon, Illinois's air quality is roughly typical for the state, where the average city posts a 5-year median AQI of 45.
For context within Illinois: Clark, Illinois currently holds the state's cleanest grade (B, AQI 34), while Rock Island, Illinois sits at the bottom (D, AQI 47).
What's in Sangamon, Illinois's Air?
The dominant pollutant in Sangamon, Illinois is Fine Particulate Matter (PM2.5). Fine particulate matter — particles less than 2.5 micrometers across — comes mostly from combustion: vehicle exhaust, wildfire smoke, residential wood burning, and industrial emissions. Because these particles are small enough to enter the bloodstream, PM2.5 is the pollutant most strongly linked to cardiovascular disease, respiratory illness, and premature death.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Fine Particulate Matter (PM2.5) | 253 | 69% |
| Ground-Level Ozone | 112 | 31% |
Is the Air Getting Better or Worse?
Air quality in Sangamon, Illinois has been getting worse over the past decade, with median AQI climbing by roughly 1.6 points per year. That bucks the national trend of broad improvement, and most often reflects either growing wildfire smoke exposure (particularly across the West) or rising local emissions from population and freight growth.
In 2014, Sangamon, Illinois posted a median AQI of 33. By 2023 that figure was 51 — a rise of 18 AQI points dirtier across 10 years of EPA records.
Year-by-Year AQI in Sangamon, Illinois
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 33 | 319 | 0 | Ozone |
| 2015 | 35 | 292 | 0 | Ozone |
| 2016 | 36 | 304 | 1 | Ozone |
| 2017 | 43 | 262 | 2 | Ozone |
| 2018 | 49 | 189 | 1 | PM2.5 |
| 2019 | 45 | 222 | 0 | PM2.5 |
| 2020 | 44 | 254 | 0 | PM2.5 |
| 2021 | 43 | 233 | 0 | PM2.5 |
| 2022 | 45 | 220 | 4 | PM2.5 |
| 2023 | 51 | 182 | 20 | PM2.5 |
Health Context for Sangamon, Illinois
Across the past five years, this area has logged just 24 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 5 days per year, or roughly one every other month. That is a low count by national standards.
Treat daily AQI forecasts as essential input. On flagged days, sensitive groups (asthma, COPD, heart disease, pregnancy, young children, older adults) should limit outdoor exertion and keep windows closed. A HEPA air cleaner sized to a bedroom or family room can cut indoor PM2.5 by 80%+ during smoke or pollution events. Because PM2.5 penetrates deep into the lungs and bloodstream, an N95 or KN95 mask provides meaningful protection on smoky or high-particulate days — surgical masks do not.
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.
Sangamon, Illinois has an Air Quality Grade of D (poor) with a 5-year median AQI of 46. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been worsening over the past decade.
This answer pulls from the EPA Air Quality System (AQS), the authoritative federal source for U.S. air quality and pollution monitoring. The headline number above is the direct answer; what follows is the additional context most readers need to use the answer for a real decision rather than just a fact lookup.
For readers turning this answer into action: cross-reference against the underlying the EPA Air Quality System (AQS) record before acting on time-sensitive decisions. The site renders the data as it was published; subsequent revisions can shift the picture, and the live federal data is always the authoritative current reference.
Source: EPA Outdoor Air Quality Data, 2026.