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Indianapolis has a reputation among locals for having “poor air quality”. It was reported in a recent WFYI article that the American Lung Association ranked the Indianapolis-Carmel-Anderson area as the eleventh most particle polluted city in their 2024 “State of the Air” report. This is a ranking based on the amount of particulate matter pollution found in the area’s air. Its reputation is furthered by its Air Quality Index (AQI) ranking: according to an EPA report for the year 2023, the metro area had the 8th highest AQI median in the country, tied with the Detroit, MI and Los Angeles, CA metro areas. What does this mean for Indianapolis?
The EPA ranking is based on the Air Quality Index (AQI). The AQI is a 0 to 500 unitless scale that measures how polluted the air is. The five major pollutants included in the AQI are ground level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and particulate matter (PM10 and PM2.5). The greater the density of pollutants in the air, the greater the AQI value. An AQI greater than 100 is considered unhealthy while those 50 and lower are considered safe, with 51-100 occupying the “moderate” level. For a full list of these levels and what they mean for human health, visit https://www.airnow.gov/aqi/aqi-basics/.
The American Lung Association ranking is based on particulate matter (PM) pollution. In Indianapolis, this is typically PM2.5, a specific type of particle pollution that includes any microscopic solids or liquid droplets less than 2.5 micrometers in diameter (30 times smaller than the width of human hair), like dust, dirt, or soot. For a good visual as to how small this is, see the diagram on this EPA website. PM2.5 particles are part of the cause of haze and smog in many parts of the US and are easily inhaled. When inhaled, these fine particles can get deep into your lungs or be absorbed into the bloodstream and cause health problems.
Of the measured pollutants in AQI, PM2.5, Indy’s main pollutant, poses the greatest health risk according to the United Nations Environment Programme. High PM2.5 concentrations exacerbate respiratory issues like COPD or asthma. PM2.5 is also linked to health effects like stroke, heart disease, lung disease, and cancer. According to the New York Department of Health’s website, studies have linked increased rates of specific conditions, higher cardiovascular and respiratory hospital visits, and exposure to particulate matter to one another. The most at-risk groups for these effects from particle pollution tend to be people with heart and breathing problems, children, pregnant women, and older adults. For more health effects of particulate matter, see this EPA site.
The high PM2.5 levels in Indianapolis can be compared to those of well-known polluted cities in California. IQAir, which gets its data from many government and non-profit contributors, states that Indianapolis air quality is ranked 53rd (out of 1517 US cities with recorded annual AQI) for worst particle pollution, tied with South Pasadena, CA. As of 2019, even Los Angeles had less particle pollution: its annual PM2.5 average was 12.7 μg/m3 whereas Indy’s was 13.4 μg/m3. According to CEIC data, the Indianapolis-Carmel-Anderson area levels of PM2.5, the main pollutant present in Indy’s air, average at a 51.000 AQI median from January of 1999 to the present date (using 9300 recorded observations). This is a “poor” air quality index rating. Even when the AQI is at a “fair” rating (best rating with little to no risk), individual principal pollutants can exceed the WHO standard limits. In Indianapolis, it is often PM2.5 that is above the WHO limit, making long-term exposure a health risk.
Why are the PM2.5 levels high in Indianapolis?
PM2.5 is the result of manmade sources like construction sites, smokestacks, car exhaust pipes, roads, vehicles like buses and semis, and combustion processes (reaction when something is burned). This pollution can also result from natural occurrences like wildfires, volcanoes, dust storms, and sandstorms. Indy has many manmade sources because of a high presence of construction, roadways, vehicular traffic, and manufacturers that release emissions from smokestacks. Weather can contribute to PM pollution, as levels tend to be higher on days with less wind or air mixing.
How is air quality data collected and reported?
AQI is measured using ground-level instruments and satellites. Monitors can have specific pollutant detecting sensors on them, use lasers to scan density of particulate matter per cubic meter, or use satellite imaging to measure energy reflections and emissions and calculate pollutant presence. Governmental, crowd-sourced, and satellite-derived air quality monitors are used together with weighted values based on reliability and which pollutant was measured to produce a total AQI reading. For more see https://www.unep.org/news-and-stories/story/how-air-quality-measured.
Pollutant emission reporting regulations exist and are upheld by state governments in order to monitor health risks like PM2.5 pollution. The EPA has also produced air dispersion software to estimate concentrations or the deposition of pollutants from sources like industrial smokestacks. The EPA often runs this program for regulatory purposes, but the software is available for public use. Environmental professionals, such as Mundell, use the software to assist companies in maintaining regulatory standards, tracking emissions, or challenging conclusions made by the EPA. To learn more about emissions regulations, air dispersion modeling, and Mundell’s services, see this related article.
Tools to view local air quality
You should check the AQI projection every day before you decide to spend an extended time outside. Individuals with respiratory or cardiovascular issues should check the AQI every time they will be exposed to outside air (this includes leaving windows open) to limit health risks. There are many websites available that show current, past, and predictions of the AQI and its individual components.
Specifically for Indiana, you can use IDEM’s SmogWatch site to view ground-level ozone and PM2.5 ratings per Indiana county for the current day and the forecast for the next day. You can also use the “Current Air Quality Index” map to view the current ozone and PM2.5 concentrations by monitor on a national level.
Visit AirNow (or look at their interactive map) to see current air quality in locations across the country. The website shows a map of AQI level in your area, an air quality forecast, specific levels of PM2.5, ozone, and PM10, your current AQI numerically and by scale, and gives health recommendations.
IQAir displays current and weekly levels of AQI and pollutant presence based on more specific monitoring locations. It includes a wind map with AQI on it as well, the source the data is coming from, the pollen index, health recommendations, and pollution concentrations for PM2.5, ozone, CO, and nitrogen dioxide. If you have an air monitor, you can become a source contributor as well.
Air.plumelabs shows a map of background and city pollution with city population and plume index. Once selecting your city, you can see hourly AQI predictions and live tracking compared to annual averages. The site also gives what outdoor activities/exposures are safe compared to WHO limits. Four main pollutants are listed with their specific AQI and their concentration.
Each of these websites typically has a small difference between reported AQI based on what source they are using.
Air quality measurements are complex, but once the concept of AQI and the principal pollutants present in your area are understood, protecting your respiratory and cardiovascular health when air quality is low becomes much easier.
More resources
Indiana’s Historical Air Quality Website has data for each geographic area in Indiana (Indy is Central) available for download from the IDEM database.
Activity Guides link is a site that includes descriptions of what activities are safe at each level of AQI. These are available for different pollutants as well.
AQI Levels of Concern Website can be used to familiarize yourself with AQI levels of concern.
NOAA – AQI Data Collection is a NOAA website, geared towards kids, that has good explanations of AQI and where the data comes from.
