Air Quality Index Basics

The Air Quality Index (AQI) is a scale used to communicate the impact of air quality conditions on public health. 

The AQI represents the amount of an air pollutant on a scale from 0-500. The higher the value the greater the level of pollution and potential health risk. The values are sorted into six color-coded categories ranging from "Good" (1-50) to "Hazardous" (301-500). While there is no "healthy" amount of air pollution, any AQI value below 100 is considered to be acceptable for public health. 

The Air Quality Index

AQI Value

Category (Color)



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.

301 and above

Hazardous (Maroon)

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


AQI Pollutants

The AQI is calculated for five common air pollutants monitored in our air: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Two pollutants, ozone and fine particle pollution, are generally the highest, and therefore set Louisville’s AQI.

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. 

AQI Dashboard

The first page of this dashboard visualizes Daily AQI values by year or month, and can be filtered further by pollutant, year, or AQI category. The second page of this dashboard visualizes how often each pollutant set the daily AQI, or were the “Top Pollutant” for the day, during a given year and the makeup of those days for each pollutant by AQI category.


Not working or too small? Open the Air Quality Index Dashboard in a new tab


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