Millions of residents across Indiana were told to avoid using drive-thrus and limit certain everyday activities on Thursday as air quality alerts were issued statewide due to rising ozone levels expected to reach unhealthy thresholds.
The Indiana Department of Environmental Management (IDEM) declared an Air Quality Action Day effective across nearly the entire state of Indiana, encompassing roughly 7 million people, with alerts remaining in effect until midnight local time. Officials warned that ozone pollution could reach levels classified as “Unhealthy for Sensitive Groups,” prompting guidance to reduce emissions and protect public health.
The alert comes as warm early-summer temperatures and strong sunlight create ideal conditions for ozone to build across the region. Ozone forms when pollutants from vehicles and other sources react in heat and stagnant air, meaning spikes are more likely during hotter stretches. These seasonal conditions can push air quality into unhealthy ranges, particularly in densely populated areas where emissions are higher.
Among the most notable recommendations: residents were urged to avoid using drive-thru services and instead combine errands into a single trip, carpool, or use public transportation. Authorities also advised drivers to turn off engines when idling for more than 30 seconds, citing vehicle exhaust as a key contributor to ozone formation.
The alerts cover a broad swath of the state, including major population centers such as Indianapolis, Fort Wayne, Evansville, and South Bend, as well as smaller communities like Noblesville, Carmel, Bloomington, and Terre Haute. In total, millions of residents are affected.
“Ozone levels are expected to be in the Unhealthy for Sensitive Groups range,” the alert states, warning that active children and adults, as well as people with respiratory conditions such as asthma, should limit prolonged outdoor exposure. Those groups are considered particularly vulnerable to the effects of air pollution.
A Code Orange alert—indicating potential health impacts for sensitive populations—was also issued in parts of southern Indiana, including areas near Louisville. Officials said the general public is less likely to be affected but advised caution regardless.
How Does Ozone Form?
Ground-level ozone—the type driving air quality alerts—forms through a chemical reaction rather than being emitted directly. It is created when pollutants known as nitrogen oxides, largely from vehicles and power plants, and volatile organic compounds, from sources like gasoline vapors, solvents, and industrial emissions, react in the presence of sunlight.
Sunlight provides the energy that triggers these reactions, breaking apart pollutant molecules and allowing them to recombine into ozone.
Unlike pollutants that are directly released, ozone is considered a “secondary pollutant,” meaning it builds over time as emissions accumulate and react—often peaking in the afternoon during summer heat. This is why air quality alerts, like those issued in Indiana, are most common during warm weather and in areas with heavy traffic or industrial activity.
The spike in ozone is being driven by a combination of high temperatures, sunlight, and light winds—conditions that allow pollutants from vehicles, industrial emissions, and other sources to accumulate and chemically react in the atmosphere. These reactions produce ground-level ozone, a key component of smog.
To help limit the buildup of ozone, authorities outlined several steps residents can take. In addition to avoiding drive-thrus and unnecessary trips, the public was asked to delay refueling vehicles or using gasoline-powered lawn equipment until after 7 p.m., when conditions are less favorable for ozone formation. Energy conservation measures were also recommended, including setting air conditioners to 75 degrees or higher and turning off lights when not in use.
Similar advisories were issued in areas bordering Ohio and Kentucky, where regional air quality agencies warned that ozone levels could approach or exceed unhealthy standards. Residents in those areas were given parallel guidance, including avoiding vehicle idling, refueling after evening hours, and postponing yard work involving gas-powered equipment.
What Happens Next
While the current alert is set to expire at midnight, officials said conditions could evolve depending on weather patterns and pollution levels. They urged residents to monitor updates from IDEM and local air quality agencies.
Public health officials stressed that small behavioral changes—such as skipping a drive-thru stop or combining multiple errands—can collectively help reduce emissions during critical periods.
The alerts come amid a broader pattern of early summer ozone events, as warmer temperatures and increased sunlight create conditions conducive to smog formation across the Midwest.
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