Ozone in Louisville

Ozone is a colorless gas that occurs both in the Earth's upper atmosphere and at ground level. In the upper atmosphere it forms a protective layer that shields us from the sun's rays. In our breathing air at ground level it is a harmful air pollutant that can cause a variety of health impacts including coughing, irritated lungs or throat, and difficulty breathing, especially for elderly adults, children, and those with lung conditions like asthma.

The amount of ozone in the air is monitored in real time throughout the country and is one of the pollutants that determines an area's Air Quality Index as well as attainment of the National Ambient Air Quality Standards set by the federal Clean Air Act. It is one of the two pollutants that is forecast in the Louisville area. Many urban and suburban areas throughout the United States have high levels of ground-level ozone. 

How Ozone Forms

Ozone is not emitted directly into the air, but is created by a complex chemical reaction in our air between heat, sunlight, nitrogen oxides (NOx), and volatile organic compounds (VOCs). Major sources of NOx and VOC include emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents.

In addition to the need for sunlight and heat, other weather conditions like wind, heat, and rain can have a significant impact on the formation of ozone. Conditions like wind, humidity, and rain can limit ozone formation. Due to the fact that sunny, warm, still, and dry conditions that help create ozone are more common during summer months, March-October is considered ozone season. 

infographic on the formation of ground-level ozone
Louisville's Ozone Status

The Louisville area is currently designated as "non-attainment" of the most recent National Ambient Air Quality Standard for ground-level ozone. The APCD's monitoring data from 2019-2021 show that Louisville's air is now meeting the standard, and the area is currently applying for redesignation to "attainment".

graph of Louisville's ozone attainment status

Resources on Ground-Level Ozone:

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