Criteria Pollutant Monitoring

Criteria pollutants are six commonly-occurring pollutants that have been deemed harmful to public health and the environment through the Clean Air Act.

The APCD monitors for these pollutants at six monitoring stations throughout Louisville Metro to determine the area’s attainment with National Ambient Air Quality Standards as well as the Air Quality Index (AQI). The methods used for criteria pollutants are strictly regulated by EPA and standardized across the country.

The pollutants are: ground-level ozone (O3), Particle Pollution (PM10 and PM2.5), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO2), and lead (Pb).

Air Quality Index

The Air Quality Index (AQI) is tool to used to communicate the impact of air quality on health. It calculated for five criteria pollutants: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Live AQI values measured at through the APCD's monitoring network are shared through Louisville Air Watch. Historical AQI Values can be accessed using the EPA's Air Data website. 

Dots around Louisville map signaling the live AQI
Louisville Air Watch provides live AQI values from APCD's monitoring sites.

National Ambient Air Quality Standards

The monitored levels of pollutants also determine Louisville's attainment of the National Ambient Air Quality Standards (NAAQS), which are set through the Clean Air Act. Louisville's current status for each standard is in the table below. 

Pollutant Standard Louisville Status
Carbon Monoxide Highest 8-hour average below 9 ppm
Highest 1 hour average below 35 ppm
Lead1 Three month rolling average below 0.15 µg/m3 Attainment
Nitrogen Dioxide

Annual average below 0.053 ppm
Highest 1-hour average below .10 ppm

Sulfur Dioxide Highest 1-hour average below .75 ppm
Highest 3-hour average below .5 ppm
Particulate Matter (PM10) Highest 24-hour average below 150 µg/m3 Attainment
Particulate Matter (PM2.5) Annual average below 12 µg/m3
Highest 24-hour average below 35 µg/m3
Ozone Highest 8-hour average below .070 ppm Nonattainment2

1In 2016, the EPA authorized the APCD to discontinue active monitoring of airborne lead (Pb) because levels are far below the NAAQS and are not expected to increase at the present time.

2Air Monitoring data show that the Louisville area is now meeting the standard for Ozone. The APCD currently has a request to redesignate the area to Attainment pending EPA approval. 


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