Marion County earned an F for both ozone and particle pollution in the most recent State of the Air report. Indianapolis-Carmel-Muncie now sits 21st on the national worst-list for short-term particle pollution. That's the headline most Hoosiers haven't read yet, and it's why this map matters.
After manufacturing filters for over a decade and serving more than two million households, we know what happens next. Outdoor AQI doesn't stay outdoors. The same particles a Marion County monitor flags at noon are circulating through your bedroom by dinner if nothing catches them on the way in.
The live readings below come from EPA AirNow stations across Indianapolis, Fort Wayne, Bloomington, and Evansville. Underneath the map, you'll find what those numbers mean for the people most at risk in your house, what's driving them this week, and the indoor moves that hold up when outdoor air refuses to.
The live map above shows real-time AQI readings for Indianapolis, Fort Wayne, Bloomington, Evansville, and the rest of the state. Indiana's calm-day baseline runs from 25 to 75 on the AQI scale, with documented spikes during ozone season, pollen peaks, and wildfire smoke transport events.
0 to 50 (Good, green): Safe for everyone, all activities
51 to 100 (Moderate, yellow): Acceptable for most, though sensitive individuals may notice symptoms
101 to 150 (Unhealthy for Sensitive Groups, orange): Knozone Action Day territory, where sensitive groups should limit outdoor exertion
151 to 200 (Unhealthy, red): Reduce outdoor activity for everyone
201+ (Very Unhealthy / Hazardous, purple/maroon): Stay indoors and run the HVAC fan continuously with a fresh, properly rated filter
Ground-level ozone (May through September)
PM2.5 from vehicle emissions and industrial sources
Transported wildfire smoke from Canadian boreal fires
Every morning during May through October, twice daily during active smoke events, and before any extended outdoor activity for sensitive groups year-round.
Outdoor AQI determines indoor air quality without active filtration. Filters from Indiana customers run measurably dirtier during the summer months than winter ones.
Indiana's pollution sources stack. Vehicle emissions, ozone formation, agricultural burns, and Canadian wildfire smoke can all hit the same week.
Knozone Action Days are Indiana's early warning system. Sign up at smogwatch.in.gov to get alerts before unhealthy air arrives.
Sensitive groups span roughly 1 in 5 Marion County residents. Children, older adults, pregnant individuals, outdoor workers, and anyone with asthma, COPD, or heart disease should treat AQI checks as a daily habit during ozone season.
Indoor protection works. Closed windows, continuous fan, and a fresh filter make a measurable difference, and a properly rated filter handles the rest.
The Air Quality Index is EPA's 0-to-500 scale. It packs ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide into a single number you can read at a glance. Indiana's calm-day baseline runs between 25 and 75. The bands climb from Good (0 to 50, green) through Moderate, Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, and finally Hazardous (maroon, 301 to 500). Anything above 100 means somebody in your house should pay attention.
Most of Indiana's worst air days don't get cooked up in Indiana. Chemistry you can't see, and weather patterns transporting smoke from a thousand miles north do most of the damage.
Three forces dominate. Vehicle emissions along I-65, I-70, and I-465 release nitrogen oxides that cook into ozone every time the sun gets aggressive. Industrial activity across Marion, Lake, and Porter counties adds particulate matter and volatile organic compounds. The wild card, increasingly the loudest one, is transported wildfire smoke from Canadian boreal fires that has driven repeated multi-day air quality alerts in Indiana since 2023.
Stack seasonal pollen, late-summer agricultural burns, and fall harvest dust on top of that, and you get a year-round pollutant calendar that shifts almost weekly.
The Indianapolis Office of Sustainability runs the public alert program called Knozone. When forecasted ozone or PM2.5 is expected to reach the Unhealthy for Sensitive Groups range, the city declares a Knozone Action Day. On those days, the city advises sensitive groups to limit outdoor exertion, including children, older adults, pregnant individuals, outdoor workers, and anyone managing asthma, COPD, or heart disease. Hoosiers can subscribe to text or email alerts at smogwatch.in.gov so the warning arrives before the air does.
Knozone Action Days cluster from May through September, when ozone formation peaks. They also show up during stagnant late-summer or early-autumn weather windows that trap PM2.5 close to the ground.
Indianapolis carries the worst grades in the state. The State of the Air F for both pollutants isn't an accident. Urban heat island effects, dense I-465 traffic, and the city's central position in the smoke transport corridor combine to push monitors higher here than anywhere else in Indiana. The Indianapolis live AQI map shows real-time readings from individual stations, including the West 18th Street and I-70 corridor monitors.
Fort Wayne usually breathes cleaner than Indianapolis, but not always. The I-69 corridor and proximity to Lake Michigan smoke transport patterns can spike summer PM2.5 sharply. Industrial activity around the St. Joseph and Maumee River basins adds local particulate sources during temperature inversions.
Bloomington tends to post the cleanest summer averages in central and southern Indiana, helped by elevation and lighter traffic density. IU campus seasonal swings and historical limestone quarry dust during dry weeks can push spring readings into the Moderate range. Pollen from the surrounding hardwood forests is more often the local concern than industrial emissions.
Evansville sits in the Ohio River valley, which creates atmospheric basin effects that trap pollutants during temperature inversions. Power generation and barge traffic along the river produce a particle pollution profile that doesn't look like northern or central Indiana.
Indiana's pollen calendar runs harder than most states'. Tree pollen from oak, maple, birch, and sycamore takes over from late March through May. Grass pollen runs the show from May through July. By August, fall ragweed combines with agricultural harvest dust through October, which tends to be the worst stretch of the year for allergy and asthma sufferers.
Pollen counts don't always show up on the official AQI band, because AQI tracks ozone and particulates rather than allergen concentrations. Cross-reference local pollen forecasts with AQI when planning outdoor time during transition seasons.
Smoke from Canadian boreal fires has become a regular feature of Indiana summers. In 2023, transported smoke triggered Knozone Action Days across multiple weeks in June and July. The pattern repeated in 2024 and again in 2025. PM2.5 from these events can stay elevated for 3 to 7 days at a time. On the worst stretches, you can see the haze hanging over downtown Indianapolis from the highway.
When wildfire smoke is in play, the AQI band can shift from Good to Unhealthy in under 12 hours as a smoke plume moves through. Checking the map twice a day during summer is a reasonable habit for anyone in a sensitive group.
Daily forecasts come from a combination of NOAA modeling, EPA AirNow data, and IDEM meteorologists who issue SmogWatch advisories for ozone and fine particulate matter. Forecasts are most reliable 24 to 48 hours out. They tend to slip during fast-moving smoke events. Knozone Action Day declarations usually arrive 12 to 24 hours before the unhealthy conditions show up.
A few specific changes inside your house make the biggest difference once the outdoor AQI in Indiana climbs past 100.
Close windows and doors. Fresh air isn't always clean air.
Switch your HVAC fan to continuous instead of auto. More cycles through your filter means more particles captured.
Check your filter weekly during ozone season and smoke events. A loaded filter passes contaminants instead of holding them.
Step up to a higher-rated filter during the months when AQI spikes are predictable. Spring through early fall is when most Indiana homes benefit.
Skip indoor pollution sources when outdoor air is already loaded. Candles, the wood-fire pizza experiment, and deep-frying nights all add to what your filter has to handle.
Our customer data from Indiana ZIP codes confirms the pattern. Filter returns from June, July, and August arrive at significantly higher loading levels than winter shipments. That's direct evidence that outdoor AQI does what the maps suggest, only quietly, inside the homes that don't take action.
In Indiana, we see something that catches a lot of homeowners off guard: the same week that brings spring pollen also brings the first ozone alerts of the season, and by July, the wildfire smoke transport adds a third layer most filters aren't sized for. The right MERV rating during those weeks isn't a comfort decision. It's a respiratory one.
— Filterbuy Team
Seven authorities Hoosiers can lean on for context, alerts, and indoor-protection guidance. Each one comes from a federal, state, or city source that publishes Indiana data directly.
Real-time monitor-by-monitor readings, forecasts, and current AQI for every Indiana city with active monitoring.
IDEM’s near-real-time statewide maps, pollutant concentrations, and meteorological data through the Data Management and Display System.
Source: Indiana Department of Environmental Management (IDEM) Air Quality Data
The city’s sustainability program page with current Action Day declarations, historical records, and resident action steps.
Annual State of the Air grades, pollution rankings, and population-at-risk data for the Indianapolis metro region.
Source: American Lung Association Indianapolis-Carmel-Muncie Metro Page
Practical guidance on protecting homes during smoke events, including clean room setup and HVAC filter recommendations.
Health-effects breakdown of particulate matter and ozone with specific guidance for sensitive groups.
Source: CDC Air Pollutants Explainer
Local forecast office page with regional weather and air quality outlooks specific to central Indiana.
Three figures Indiana homeowners should know:
The Indianapolis-Carmel-Muncie metro area averages 9.8 unhealthy particle pollution days per year, and Marion County received an F grade for both ozone and particle pollution in the American Lung Association’s 2025 State of the Air report.
Source: lung.org State of the Air, Indianapolis-Carmel-Muncie metro
EPA research shows indoor pollutant concentrations are often 2 to 5 times higher than outdoor levels, meaning Indiana’s outdoor AQI directly shapes the air most Hoosiers actually breathe every day.
Approximately 9.7 percent of Indiana adults, around 647,729 people, currently live with asthma according to Indiana State Department of Health data based on CDC Behavioral Risk Factor Surveillance System reporting.
Source: Indiana State Department of Health, Respiratory Health Data and Reports
Tracking the AQI map matters, but it doesn't change anything on its own. The map tells you what you're up against. It doesn't change what gets into your bedroom, your kid's nursery, or the chair you read in. That's the homeowner's job, and it's where the real difference happens. Hoosiers shouldn't have to rebuild their lives around a Knozone alert. They should be able to keep living and trust their filtration to handle the rest. That's the entire reason we make what we make.
Three things to do before the next high-AQI day in Indiana:
Bookmark this page. Check it each morning during ozone season (May through September) and during any active wildfire smoke event. The map updates hourly from EPA monitoring stations.
Subscribe to alerts at smogwatch.in.gov. Knozone Action Day declarations will reach you before the air does. Text and email options are both free.
Inspect your HVAC filter today. If it's been in place longer than 30 days during pollen or smoke season, replace it. A fresh filter at the start of a high-AQI stretch will hold more contaminants over the next 30 days than a half-loaded one starting out.
Three things drive Indianapolis air quality. Ground-level ozone forms quickly on hot, sunny, low-wind afternoons from May through September. Vehicle emissions along I-65, I-70, and I-465 add particulate matter. Transported smoke from Canadian wildfires has triggered multi-day Knozone Action Days every summer since 2023. Check the map above for current readings and the Indianapolis Office of Sustainability for any active Knozone declaration.
A Knozone Action Day is an air quality alert from the Indianapolis Office of Sustainability. The city declares one when forecasted ozone or PM2.5 is expected to reach the Unhealthy for Sensitive Groups range (AQI 101 to 150, the orange band). On those days, the city advises sensitive groups to limit outdoor exertion and asks all residents to reduce their contribution to ozone formation through actions like avoiding vehicle idling and skipping gas-powered lawn equipment.
Indiana pollen runs in three overlapping waves:
Tree pollen: late March through May (oak, maple, birch, sycamore)
Grass pollen: May through July
Ragweed and harvest dust: August through October
None of this always shows up on the official AQI band, so allergy sufferers should cross-reference local pollen forecasts during transition seasons.
Check the live map above for current PM2.5 readings. Indiana sees transported wildfire smoke from Canadian boreal fires most often in June, July, and August. When smoke is present, PM2.5 can climb from Good to Unhealthy within 12 hours as a plume moves through. The EPA Wildfires and Indoor Air Quality page (linked in Resources above) has detailed guidance for protecting homes during smoke events.
Subscribe at smogwatch.in.gov for text or email notifications. The Indianapolis Office of Sustainability also posts updates on social media via @SustainIndy. AirNow's mobile app sends push notifications for any monitor you choose to follow.
EPA recommends a MERV 13 filter or higher for capturing fine particulate matter from smoke and combustion sources, set as high as your HVAC system can accommodate. According to EPA, most furnaces and home HVAC systems can run a MERV 13 filter without equipment problems, provided the filter gets replaced frequently. For older or undersized systems, EPA suggests consulting a qualified HVAC technician to determine the highest-efficiency filter your specific system will support. EPA also notes that during heavy smoke or ozone events, you should replace the filter more often than the manufacturer's default schedule. Per EPA, swap any filter that looks visibly dirty (dark brown or black). The full EPA filtration guidance, including instructions for sealing your home and creating a cleaner-air room during smoke events, is on the EPA Wildfires and Indoor Air Quality page (linked in Resources above).
The map pulls hourly readings from EPA AirNow monitoring stations operated by IDEM and partner agencies across the state. Readings are preliminary and subject to validation. For the most precise interpretation, check both the AirNow map and IDEM's Data Management and Display System.
Ozone (O3) is a gas that forms when sunlight reacts with vehicle and industrial emissions. It peaks on hot, sunny afternoons and is most dangerous to the lungs. PM2.5 is fine particulate matter (less than 2.5 micrometers in diameter) from combustion, dust, smoke, or chemical reactions. PM2.5 reaches the deepest parts of the lungs and crosses into the bloodstream, which makes it dangerous for both cardiovascular and respiratory health.
For real-time city-level readings (including the West 18th Street and I-70 corridor monitors), check our dedicated Indianapolis page linked in the Cities to Watch section above.
To make sure your indoor air handles whatever the outdoor AQI throws at it, browse Filterbuy's filter selection by size and rating. Made in Alabama, Florida, Pennsylvania, and Utah. Shipped directly from our factory to your door.
