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Air Quality

Air Quality Information

Air Quality is a problem for everyone, but each one of us and our organizations can be part of the solution. The choices we make every day can decrease air emissions and help protect our health as well as our employees and the people around us. We have the power to change our homes, workplace, transportation, and consumer habits in ways that reduce air emissions. This page is to help you understand air quality and the effects of increased ground-level ozone and particulate matter 2.5, commonly referred to as PM 2.5.


Ozone, a pungent pale blue gas, exists both in the upper and lower atmosphere and has good and bad effects depending on where it is located. In the upper atmosphere, or stratospheric layer, ozone shields us from the sun’s damaging rays. In the lower atmosphere, or tropospheric layer, our breathing zone, it poses a health hazard. Ground-level ozone occurs when strong sunlight and hot weather mixed with emissions result in harmful ozone concentrations in the air we breathe. The air quality action season for ground level ozone in Indiana is March 1 through October 31 when the sunlight is strong, and the weather is hot.

Fine particles, also known as particulate matter 2.5 or PM 2.5, are solid particles or liquid droplets 2.5 microns or smaller in size (less than one one-hundredth of a grain of salt) that can irritate the air sacs in the lungs. Particulate Matter 2.5 can be naturally occurring (pollen, spores, dust) or manmade (open burning, emissions), and can be suspended in the air for long periods of time. Some of these particles are large or dark enough to be seen by the human eye such as soot or smoke, while others are so small, they can only be detected by an electron microscope. There is no season for PM 2.5 as action days can occur year-round.

Ground-level ozone and PM 2.5 have been linked to a series of health problems including: increased wheezing or coughing, chronic bronchitis, decreased lung function, and increased eye and nose irritation. Those most at risk of these health problems include, older adults, children, those with respiratory problems, such as asthma, and people who are active outdoors.

Air Quality Index and Air Quality Action Days

Air Quality Index (AQI) is used for monitoring, forecasting, and reporting the daily air quality for ground-level ozone and PM 2.5 based on the National Ambient Air Quality Standards set by the Environmental Protection Agency. Air Quality Action Days are days in which ground level ozone and PM 2.5 are predicted to reach unhealthy levels in outdoor air based on the Air Quality Index. The Indiana Department of Environmental Management (IDEM) and the Environmental Protection Agency (EPA) employ a team of forecasters who analyze weather patterns, ozone concentrations, and particulate matter to determine if ground level ozone and PM 2.5 may reach unhealthy levels. When this data indicates that conditions are right for increased levels of these pollutants, an air quality action day is put into effect.

The IDEM will issue an air quality action day for the following air quality index and pollutant predictions:

Air Quality Action Days

Health impacts associated with these Air Quality Index categories are:

  • High Moderate (Code Yellow): Occasionally, an air quality action day is declared when the air quality index is in the High Moderate range and the levels are expected to approach Code Orange levels. Health alerts issued under these conditions are intended to inform the public that there may be a moderate health concern for individuals who are unusually sensitive.
  • Unhealthy for Sensitive Groups (Code Orange): This triggers a health alert to inform the public about potential impacts to sensitive groups, including people with lung disease, older adults, and children who are more vulnerable to ozone, and people with heart and lung disease, older adults and children who are more vulnerable to PM2.5.
  • Unhealthy (Code Red): This triggers a health alert to inform the public that everyone may begin to experience some adverse health effects and members of sensitive groups may experience more serious effects.
  • Very Unhealthy (Code Purple): This triggers a health alert to inform the public that everyone may experience more serious health effects.
  • Hazardous (Code Maroon): This triggers a health warning of emergency conditions that are more likely to affect the entire population.

Members of the Partners for Clean Air Program develop Air Quality Action Plans, which are designed to be implemented on Air Quality Action Days (AQADs) as a way of reducing these harmful air pollutants. A list of voluntary actions you and/or your organization can take to reduce ground-level ozone and PM 2.5 are provided on our Air Quality Tips page. History, research, and further details regarding air quality, pollutants, and other helpful websites are available on the Resources page.

Are you or your organization are ready to take action and be part of the solution? Become a Member.

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