Illinois Ranks 4th Worst in the Nation for Air Quality. Here's What Corn Has to Do With It.

By Tara Desmond, Strategic Digital Marketing Manager, IL Corn

Illinois has some of the worst outdoor air in America, and most residents have no idea. This article breaks down where the state ranks, why, and what it means for the air inside Illinois homes -- written for the growers, families, and communities that make up Illinois corn country.

Based on 2023 EPA monitoring data, Illinois's population-weighted average Air Quality Index is 50.4, ranking 48th out of the 50 states and Washington, D.C. Only Arizona, Nevada, and New Mexico rank worse. An AQI under 50 counts as "Good," and 47 of the 51 ranked make that cut. Illinois does not.

The Numbers at a Glance

Measure	Figure
Illinois average AQI (2023 EPA data)	50.4 ("Moderate")
Illinois national rank	48th of 51
States/D.C. with a "Good" average AQI	47 of 51
Indoor air pollution vs. outdoor (EPA estimate)	Typically 2 to 5x higher
Share of time the average American spends indoors	Roughly 90%
Air filters used by U.S. households annually	An estimated 500 million

Why Does Illinois Rank So Low?

The AQI tracks major pollutants, including ground-level ozone and fine particulate matter (PM2.5), on a 0-to-500 scale. Illinois sits just above the "Good" line at 50.4, in "Moderate" territory. The state figure is population-weighted, meaning the Chicago metro area, with its traffic density and industrial activity, carries significant weight in the average. The American Lung Association's State of the Air report has consistently ranked the Chicago metro among the more challenged regions for ozone.

Downstate readings are generally more favorable. Conditions vary by county and by season, so the state average tells only part of the story. Real-time local readings are available at AirNow.gov.

For the roughly 1 in 13 Americans living with asthma, according to the CDC, these numbers shape daily decisions. For farm families who spend far more time outdoors than the average American, they can matter even more.

The Bigger Surprise: The Air Inside

Here is the finding most people miss. Even in a state ranked 48th, outdoor air quality is usually not the biggest air quality issue an Illinois family faces. The EPA estimates that indoor air is typically 2 to 5 times more polluted than outdoor air because homes trap pollutants from cooking, cleaning products, pet dander, dust, and building materials and then recirculate them through the HVAC system.

With Americans spending about 90% of their time indoors, the filter in the furnace often does more for the air a family actually breathes than the state's outdoor ranking suggests. The Department of Energy recommends checking that filter monthly during heavy-use seasons and replacing it regularly, typically every 60 to 90 days, depending on the home. Industry groups like ASHRAE treat filtration in the MERV 8-13 range as a core tool for indoor air quality.

Where Illinois Corn Comes Into the Home

American households use an estimated 500 million air filters a year, and nearly all are made from petroleum-based synthetic materials. That is beginning to change, and corn is the reason.

Corn starch can be fermented into lactic acid and converted into PLA, a renewable plant-based polymer produced at a commercial scale by companies like NatureWorks and verified through the USDA BioPreferred program. Aerterra, a winner of the National Corn Growers Association's Consider Corn Challenge, spins corn-based PLA into nanofiber filter media and manufactures HVAC filters in the United States in the same MERV 8, 11, and 13 ratings consumers already know.

The demand structure is what makes this new use notable for growers. Filters are replaced every 1 to 3 months in nearly every home with forced-air heating or cooling, so each household that switches represents recurring corn demand rather than a one-time sale. Illinois's air quality challenge is largely urban and industrial, but the crops grown in Illinois fields are now part of how families address the air inside their homes.

Three Things Illinois Families Can Do This Week

Check the filter. If you cannot remember the last time you changed it, it is likely overdue. A clogged filter recirculates the particles it should be catching, forcing the system to work harder. Learn more about how often to change your home air filter.

Match the MERV rating to the household. MERV 8 covers everyday dust and pollen; MERV 11 adds pet dander and finer smog particles; and MERV 13 captures fine particulate and smoke, which matter most for allergy and asthma sufferers. Check your system's specifications before upgrading, as some systems handle higher ratings better than others. Read our full MERV 8 vs. MERV 11 comparison.

Watch the local number, not just the state's. Illinois's 50.4 average hides significant county-to-county differences. AirNow.gov shows real-time readings by ZIP code.

Corn's Other Air-Quality Connection: Ethanol

The connection between corn and air quality doesn't stop at the furnace filter. Ethanol made from corn is also part of the transportation sector's efforts to reduce emissions and improve fuel performance. When blended into gasoline, ethanol can replace a portion of petroleum-based fuel while providing a domestically produced, renewable alternative. Corn-based ethanol has also been shown to have significantly lower greenhouse gas emissions than petroleum-based fuel.

For Illinois, that connection is especially significant. The state has 14 ethanol plants that employ more than 22,000 people and generate $11.4 billion in economic output. Illinois corn farmers supply the feedstock for this industry, creating a direct connection between the state's corn fields, rural communities and the fuel used by drivers across the country.

Corn's air connection is broader than it first appears: corn can become a renewable transportation fuel through ethanol and a renewable material for filtration through PLA. In both cases, Illinois corn is contributing to technologies and products designed to address environmental challenges, while creating jobs and economic activity here at home.

Frequently Asked Questions

Where does Illinois rank for air quality in 2026?

Illinois ranks 48th out of the 50 states and Washington, D.C., based on 2023 EPA monitoring data compiled in Aerterra's 2026 Air Quality by State report. Its population-weighted average AQI of 50.4 falls in the "Moderate" category, making Illinois one of only four states above the "Good" threshold.

How does ethanol fit into the corn and air-quality story?

Corn is used to produce ethanol, a renewable fuel that is blended into gasoline and used in vehicles across the country. Ethanol can reduce the amount of petroleum-based gasoline needed and has a lower lifecycle carbon intensity than gasoline, although the total environmental benefit depends on how the corn is produced and the fuel is made and used. For Illinois, one of the nation's largest corn-producing states, ethanol provides another important connection between the state's corn crop and efforts to reduce transportation-related emissions.

What is the AQI, and what counts as good?

The Air Quality Index measures major pollutants, including ozone and fine particulate matter, on a 0-to-500 scale. Readings from 0 to 50 are "Good," and 51 to 100 are "Moderate." Illinois's annual average of 50.4 sits just above the Good line, though daily readings vary widely by location and season.

Why is Illinois's air quality worse than that of neighboring states?

The state average is population-weighted, so the Chicago metro area's traffic and industrial activity carry substantial weight. Downstate air is generally more favorable. Local conditions should be checked using real-time tools like AirNow.gov.

Is indoor air really worse than outdoor air?

Often, yes. The EPA estimates indoor air is typically 2 to 5 times more polluted than outdoor air because homes trap pollutants from cooking, cleaning, pets, and dust, then recirculate them. Since Americans spend about 90% of their time indoors, indoor filtration usually affects daily exposure more than outdoor air does.

How often should home air filters be replaced?

Most filters should be replaced every 60 to 90 days, though homes with pets, allergies, or heavy HVAC use may need changes more frequently, every 30 days or so. The Department of Energy recommends checking filters monthly during peak heating and cooling seasons. Learn more in our guide on how often to change your air filter.

How is corn used to make air filters?

Corn starch is fermented into lactic acid, which is then converted into PLA, a renewable plant-based polymer. The PLA is spun into fine fibers that form filter media, replacing petroleum-based synthetics. Aerterra manufactures these filters domestically in MERV 8, 11, and 13 ratings using U.S.-grown corn.

What does this mean for Illinois corn growers?

Corn's role in air-quality and emissions solutions extends beyond one product. Ethanol creates demand for corn as a renewable transportation fuel, while corn-based PLA creates opportunities for renewable materials such as air-filter media. Together, these uses demonstrate how Illinois corn can move beyond traditional markets and become part of products and technologies addressing energy, emissions and indoor air quality.

Air quality data reflect 2023 EPA monitoring records and population-weighted annual averages by state. This article is for informational purposes only; AQI averages do not capture daily or seasonal variation, and filter performance varies by home and system type. For specific HVAC recommendations, consult a licensed HVAC professional.

---