Forecasting Louisville's Air Quality

Like the weather, air quality conditions can be forecast. The APCD works with the Indiana Department of Environmental Management (IDEM) to generate a forecast of some of Louisville's most common air pollutants 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 generated for two of our area's most common air pollutants; ground-level ozone (O3) and fine particle pollution (PM2.5), using the categories of the Air Quality Index, which are explained below. 
 

Forecast Description
Good Air quality is expected to be satisfactory and pose little or no risk to public health.
Moderate Air quality is expected to be acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.
Unhealthy for Sensitive Groups Members of sensitive groups may experience health effects. Others are less likely to be affected.
Unhealthy Any member of the general public may experience health effects; members of sensitive groups may experience more serious health effects
Very Unhealthy Health alert. The risk of health effects is increased for everyone.
Hazardous Health warning of emergency conditions. Everyone is more likely to be affected.


Ground-level ozone (O3) is a colorless gas that can cause or worsen coughing, irritated lungs or throat, and difficulty breathing. Ozone levels are generally higher on hot, sunny, calm, and dry days. 

Fine particle pollution (PM2.5) is a general term for a mixture of tiny solid and liquid droplets suspended in the air. When inhaled, these can cause or aggravate heart and lung issues. Sources include wood fires, industrial processes, and vehicle emissions. 

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 the AQI is expected to be Unhealthy for Sensitive Groups or worse an air quality alert is issued. 

Air Quality Alerts allow members of the public to plan ahead to reduce exposure and lower their emissions. 

How to reduce exposure and stay healthy on Air Quality Alert days:

  • Avoid heavy outdoor exertion (take more breaks and reduce intensity of exercise). 
  • If the primary pollutant is ozone, try to do any outdoor activities in the morning, when levels are lower. 
  • Pay close attention to related symptoms and make sure you have a rescue inhaler if one may be needed. 

How to lower emissions on Air Quality Alert days:

Map of Air Quality Index Values
Tools like Louisville Air Watch let you see Air Quality at monitoring sites throughout the Louisville area.
  • Use public transportation or work from home, if able. 
  • Reduce unnecessary vehicle idling, especially in places like drive-thru lanes and school car-rider lines.
  • Delay mowing your lawn or switch to lower-emitting equipment
  • Wait to refuel until after 7 p.m. 
  • Refrain from using household and workshop chemicals. 
  • Do not have a fire or other burns. Open burning is prohibited on Air Quality Alert days, even if usually legal. 
  • Businesses can pledge to reduce their emissions on Air Quality Alert days through our Air Quality Action Partners Program.

Forecasts are valuable, but monitoring the air in real time can help you navigate your day, especially if you’re more sensitive to air pollution. While many details about the weather are possible to observe merely by looking outside, air pollution is often invisible and can only be accurately measured with air monitoring equipment. 

Real-time AQI information from the APCD’s monitoring network can be found at Louisville Air Watch, and live AQI from throughout the country can be accessed at EPA’s airnow.gov.
 

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