What is Ozone?

Ozone is a gas that occurs both in the Earth’s upper atmosphere and at ground level. Ozone can be good or bad, depending on where it is found:

Good Ozone. Ozone occurs naturally in the Earth’s upper atmosphere—10 to 30 miles above the Earth’s surface.  It shields us from the sun’s harmful ultraviolet rays.

Bad Ozone. Ground level ozone is produced when organic compounds (VOC) and nitrogen compounds (NOx) react in the presence of sunlight.  These chemical compounds are called ozone precursors. Ozone precursors are of particular concern during the summer months when the weather conditions needed to form ground-level ozone normally occur.

How can ground-level ozone affect your health?

Ozone can irritate your respiratory system.  It can also reduce lung function and make it more difficult for you to breathe when you are exercising or working outdoors.

Ozone may aggravate chronic lung diseases such as emphysema and bronchitis and reduce the immune system’s ability to fight off bacterial infections in the respiratory system. Ozone can even inflame and damage cells that line your lungs.

What sources generate ozone precursors?

Ozone precursors are emitted by motor vehicles, power plants, refineries, small commercial engines, and other sources.  These sources are divided into 3 main categories – stationary, mobile and area.  Periodically, EPC is required by EPA to give an account of all precursor emissions in Hillsborough County by completing an “emissions inventory.”  This inventory represents all precursors generated in the county over a calendar year.  Click to view the most recent emissions inventory.