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Does Indianapolis have good air quality?

Indianapolis air quality has recently failed to meet Environmental Protection Agency (EPA) standards for both annual PM2.5 and ozone, two of the nation’s most pervasive and dangerous air pollutants. The excess over allowed federal limits is recent. While ozone levels have long wavered, they have been on the rise since 2015. Indianapolis PM2.5 levels, on the other hand, only exceeded federal targets in 2019 after a decade of attainment.

Ozone is one of the most poorly controlled air pollutants in the US and also one of the most dangerous. When inhaled, it aggressively attacks the lungs by reacting with the lung tissue. Breathing even small levels of ozone can potentially cause breathing problems, such as coughing, chest pain, and shortness of breath as well as long-term health problems, such as lung cancer, lung damage, and early death.

Indianapolis experiences an average of 6 annual “unhealthy” ozone days, landing the city an “F” rating by the American Lung Association (ALA).¹ According to a corresponding “State of the Air” report that aggregated data from 229 metropolitan areas, Indianapolis ranked 44th for worst ozone nationally.

For PM2.5, Indianapolis similarly struggled to meet targets, with a number of days reaching “unhealthy” levels. While a vast majority of air quality days wavered between “good” and “moderate” AQI levels, Indianapolis experienced 7 “orange” days and 1 “red” day for particle pollution.

Of the most polluted cities in Indiana for PM2.5, Indianapolis came in 2nd with a PM2.5 concentration of 13.4 μg/m³, shortly behind Harlan, Indiana with an annual PM2.5 concentration of 14.1 μg/m³. Mount Vernon ranked as the 3rd most polluted in Indiana, with a PM2.5 concentration of 12.1 μg/m³.

On a national level, Indianapolis air quality is ranked 53rd (out of 1517 included cities) for worst particle pollution, tied with the air quality of South Pasadena, California. Notoriously polluted Los Angeles has cleaner air, by comparison, with an annual PM2.5 average of 12.7 μg/m³.

8 of 12 months exceeded “good” monthly AQI averages in 2019. From worst to best, these 8 months included:

1. July (17.1 μg/m³)

2. December (17 μg/m³)

3. November (15.4 μg/m³)

4. February (15.3 μg/m³)

5. June (14.1 μg/m³)

6. March (13.9 μg/m³)

7. September (13.6 μg/m³)

8. May (12.9 μg/m³)

Where does Indianapolis ozone come from?

Ozone is known as a secondary air pollutant for its property of being formed from primary pollutants reacting in sunlight. Since ozone is not emitted directly, but rather formed from precursor pollutants with a wide range of sources, it is generally considered one of the most poorly regulated pollutants in the US. Warm and dry locations with abundant sunshine tend to have an even more challenging time managing ozone levels as ideal conditions of heat and pollution presence increase its prevalence.

Indianapolis emissions from vehicles, fuel combustion, industrial processes, and fires all contribute to the cities levels of nitrogen dioxide (NO2) and volatile organic compounds (VOCs), the two precursor pollutants necessary for ozone formation.²

Vehicular emissions tend to comprise the largest source of nitrogen dioxide (NO₂), often between 60 to 70 percent. Plants and other organic matter comprise the largest source of volatile organic compounds.

Indianapolis ozone season tends to run from May to September, when there are roughly 83 days over 80°F. Temperatures over 84°F are generally required for ozone to form. Ozone levels in Indianapolis tend to peak around the afternoon when direct sunlight is the strongest.

Is today an ozone action day in Indianapolis?

In an effort to warn the public of expected or present health risks in the air, the Indiana Department of Environmental Management (IDEM) forewarns the public of potential ozone action days. Ozone action days are hot, sunny days when ozone levels are expected to reach unhealthy levels.³

Ground-level ozone is a gas pollutant, often widespread at unhealthy levels during the summer months. It is one of six pollutants regulated by the Clean Air Act and monitored by the EPA, along with, PM2.5 and PM10 particle pollution, carbon monoxide (CO), sulfur dioxide (SO₂), and nitrogen dioxide (NO₂).

The EPA uses an Air Quality Index (AQI) to translate complex pollutant concentrations into a single easy-to-understand scale to represent health risk present in the air. Each of the six criteria pollutants are weighted and calculated for their respective health risk, or AQI number. The scale ranges from 0 to 500. Higher values indicate greater risk to health.

Ozone Action Days are announced when ozone levels reach, or are expected to reach, an AQI above 100, thus becoming “unhealthy for sensitive groups.” When the Indianapolis AQI reaches 101 to 150, “orange,” air quality is deemed risky for sensitive groups, such as children, the elderly, and those with heart or lung disease. An Indianapolis air quality rating of 151 to 200, “red,” indicates the air is “unhealthy”, and adverse health effects may also be felt by the general public.

In 2018, 18 days reached orange (unhealthy for sensitive groups) air quality in Indianapolis, while no days reached red (unhealthy) levels or higher.

Marion County, of which Indianapolis is the county seat, has roughly 450,000 residents who are sensitive to air pollution and are particularly prone to adverse health effects during ozone action days. This figure includes 91,454 residents with asthma, 60,620 with COPD, 682 with lung cancer, 71,597 with cardiovascular disease, 235,211 children under 18, 120,358 adults over 65.

What are the major air pollution sources in Indianapolis?

Major air pollution sources in Indianapolis include emissions from mobile sources, such as vehicles and trucks, stationary sources as a result of combustion and industrial processes, and area sources, such as wood burning and agriculture.

In the US, transportation is the largest contributor to air pollution, often comprising roughly half of all emissions.⁴ Indianapolis fares slightly better than the national average in terms of average commute time at 23.1 minutes compared to the national average of 25.7 minutes.⁵ 83 percent of residents commute alone. Cutting vehicular emissions by promoting electric vehicle ownership is one opportunity for significantly reducing air pollution levels in Indianapolis.

The oil and gas industry is another major pollution emitter. Indianapolis has almost 7,400 oil and gas sites that release over 370 tons of hazardous air pollution. These emissions include a combination of benzene, formaldehyde, acetaldehyde, and other compounds.⁶

Is Indianapolis air quality getting better?

After decades of air quality improvement, Indianapolis is showing signs of a new trend of worsening air quality.

While not always perfect, Indianapolis air quality has gradually improved since 1996. This steady trend towards healthier air has been driven by the Clean Air Act and its 1990 Amendments as well as increasingly stringent state and local measures aimed at reducing emissions from a wide variety of sources.

Since 2017, however, air quality levels seem to be on the rise once again. While wavering annual air quality levels are not uncommon from a long-term perspective, health experts and environmental scientists fear recent gains may be attributable to federal rollbacks by the Trump administration.⁷

Since 2017, some such changes implemented by the EPA have included:

•Abandoned requirement for petroleum companies to report methane emissions

•Removal of E15 ethanol/gasoline fuel blend ban

•Repealed the Obama administration’s Clean Power Plan

•Stopped enforcement of tailpipe emission limits on federal roadways

•Easier access to pollution permits

This trend has also been observed on a national level. A US EPA report titled “Our Nation’s Air: Status and Trends Through 2018” reveals that, while overall air quality levels appear to continue a downward trend, the rate of decline has slowed, while some pollution indicators have even been on the rise.

In Indianapolis, PM2.5 levels rose 2.2 percent from 9.9 μg/m3 in 2017 to 10.1 μg/m³ in 2018, and then another 32.7 percent to 13.4 μg/m³ in 2019. 2019 is the first year Indianapolis PM2.5 levels failed to meet federal attainment since 2012.

Indianapolis ozone levels have also been on the rise. 2013 to 2015 was the last monitoring period in which ozone levels met federal attainment levels (averaging just 1.6 unhealthy days a year). In the most recent monitoring period of 2016 to 2018, there were an average of 6 unhealthy days a year, representing a nearly 300% increase.

+Article Resources

[1] American Lung Association. (2020). State of the air – 2020.
[2] Air Georgia. (2020). Ambient air monitoring program.
[3] Public Citizen. (2018). What is ozone pollution and what is an Ozone Action Day?
[4] National Park Service. (2020). Where does air pollution come from?
[5] Data USA. (2020). Indianapolis, In.
[6] Clean Air Task Force. (2017). Health risks in Indiana from oil and gas air pollution.
[7] Saenz E. (2019, August 5). Federal report indicates end of decades-long air quality improvement.