Air Quality Forecasting

Like the weather, air quality conditions can be forecast. The APCD works with the Indiana Department of Environmental Management (IDEM) to generate the forecast using meteorological expertise and computer models, as well as local air monitoring and meteorological data.

The goal of forecasting air quality is to let the public, especially those in groups that are more sensitive to air pollution, know what the air quality is going to be like so they can plan their day accordingly. You can find Louisville's daily forecast on EPA's AirNow, as well as the APCD's Twitter and Facebook pages.
 

Forecast Basics

The forecast is created for two of our area's most common air pollutants; ground-level ozone (O3) and fine particle pollution (PM2.5).

Ground-Level Ozone

Ground-level ozone is a potentially harmful air pollutant that is not emitted directly into the air, but is created when other air pollutants (oxides of nitrogen (NOx) and volatile organic compounds (VOCs)) mix with heat and sunlight to cause a chemical reaction that produces ozone. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOC.

At higher levels ozone pollution can respiratory issues like coughing or difficulty breathing. Levels are generally higher on sunny, hot, dry, and calm summer days. 

Fine Particle Pollution (PM2.5)

Fine particle pollution (PM2.5) refers to a mixture of solid particles and liquid droplets found in the air that are 2.5 micrometers and smaller (or about 30 times smaller than the width of a human hair). When it is at higher levels in our air fine particle pollution can get into your lungs and bloodstream, causing or worsening breathing or heart ailments.

The forecast uses the categories of the Air Quality Index, a tool that is used to convey the risks that local air quality may have on individual health. Each forecast, and its meaning, is explained in the chart below. 
 

Category (Color)

Description

Good (Green)

Air quality is satisfactory, and air pollution poses little or no risk to public health.

Moderate (Yellow)

Air quality is considered acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.

Unhealthy for Sensitive Groups (Orange)

Members of sensitive groups may experience health effects. Others are less likely to be affected.

Unhealthy (Red)

Any member of the general public may experience health effects; members
of sensitive groups may experience more serious health effects

Very Unhealthy (Purple)

Health alert. The risk of health effects is increased for everyone.

Hazardous (Maroon)

Health warning of emergency conditions. Everyone is more likely to be affected.


In 2021 Louisville experienced 222 "Good" days, 136 "Moderate" days, and 7 days that were "Unhealthy for Sensitive Groups (USG)". It is uncommon for Louisville to experience air pollution in categories higher than USG. 
 

Air Quality Alerts

If air quality is forecast to be at potentially unhealthy levels (in the Unhealthy for Sensitive Groups Category or above) an air quality alert will be issued. Alerts are used to help residents avoid air pollution related health impacts; and encourage businesses and individuals to take action to reduce polluting activities. Here are some general recommendations considerations for days that are forecast to be Unhealthy for Sensitive Groups (USG):

  • Those in populations that are more susceptible to air pollution, including children, elderly adults, and those with preexisting conditions of the heart or lungs, should consider limiting outdoor activity. The higher the AQI, the more people should consider limiting their activity. 
  • As the AQI gets higher, all people should consider limiting strenuous activity outdoors. 
  • Reduce vehicle usage, attempt to carpool, work from home. 
  • Don't use gas-powered lawn equipment, wait a day or two to do the yard work. 

It is uncommon for Louisville to experience days higher than USG, but as the AQI increases the alert will affect more groups and have the potential to cause greater health issues.
 

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