What Is the Air Quality in Clark, Illinois?
Clark, Illinois has an Air Quality Grade of B (good) with a 5-year median AQI of 34. The dominant pollutant is Ground-Level Ozone, and air quality has been improving over the past decade.
Clark, Illinois Air Quality Snapshot
| Air Quality Grade | B73/100 |
| 5-Year Median AQI | 34 (Good) |
| Most Recent Median AQI (2023) | 36 (Good) |
| Dominant Pollutant | Ground-Level Ozone |
| 10-Year Trend | Improving (-0.63 AQI/yr) |
| Unhealthy Days (last 5 yr) | 6 |
| National Rank (cleanest = #1) | #189 of 1,020 (19th cleanest percentile) |
| Illinois Rank | #2 of 23 |
What Does the B Grade Mean?
Clark, Illinois earns a B — air quality is reliably in the safe range for most residents most of the time, with a 5-year median AQI of 34. Sensitive groups will see occasional caution days, but the typical resident will not need to change behavior based on air quality.
Clark, Illinois's 5-year median AQI of 34 is 7 points below the national average of 41 — meaningfully cleaner than the typical U.S. metro tracked here. Within Illinois, Clark, Illinois runs cleaner than the state average of 45 — a positive signal that local conditions (terrain, wind patterns, emission sources) are working in residents' favor.
For context within Illinois: Macoupin, Illinois currently holds the state's cleanest grade (B, AQI 33), while Rock Island, Illinois sits at the bottom (D, AQI 47).
What's in Clark, Illinois's Air?
The dominant pollutant in Clark, Illinois 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 | 358 | 100% |
Is the Air Getting Better or Worse?
Air quality in Clark, Illinois has been improving over the past decade, with median AQI dropping by roughly 0.6 points per year. That is consistent with the broader national pattern — most U.S. metros have seen steady reductions in particulate and ozone pollution since the 2010s as cleaner vehicles and power plants come online.
In 2014, Clark, Illinois posted a median AQI of 39. By 2023 that figure was 36 — a drop of 3 AQI points cleaner across 10 years of EPA records.
Year-by-Year AQI in Clark, Illinois
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 39 | 185 | 0 | Ozone |
| 2015 | 39 | 182 | 0 | Ozone |
| 2016 | 38 | 175 | 1 | Ozone |
| 2017 | 39 | 211 | 1 | Ozone |
| 2018 | 32 | 337 | 1 | Ozone |
| 2019 | 34 | 314 | 0 | Ozone |
| 2020 | 31 | 347 | 0 | Ozone |
| 2021 | 34 | 344 | 0 | Ozone |
| 2022 | 34 | 296 | 1 | Ozone |
| 2023 | 36 | 320 | 5 | Ozone |
Health Context for Clark, Illinois
Across the past five years, this area has logged just 6 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 1 days per year, or roughly one every other month. That is a low count by national standards.
For most healthy adults, current air quality in this area does not require any change in behavior. People with severe asthma, COPD, or recent cardiac events should still keep an eye on daily AQI alerts, especially during wildfire 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.
Clark, Illinois has an Air Quality Grade of B (good) with a 5-year median AQI of 34. The dominant pollutant is Ground-Level Ozone, and air quality has been improving 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.