Ozone is a special 'form' of oxygen that has three oxygen atoms arranged in a molecule and denoted as O3. Because of this chemical arrangement, ozone has some special properties that are crucial to all life on Earth (see Why is the Ozone Layer so Important?). To simplify matters, we can consider ozone in two ways: the 'good ozone' and the 'bad ozone.' The good ozone represents the O3 high in our atmosphere (the stratospheric ozone) that acts as part of the ozone shield; it will be the main focus of this section. The bad ozone is the O3 that is close to the ground (tropospheric ozone) and contributes to pollution in the form of photochemical smog.

The good ozone–that which contributes to our protective O3 layer–resides primarily in a layer between 6-25 miles (10-40 km) above Earth’s surface. It is located in a layer called the stratosphere. Most all of the weather we are familiar with resides in the lowest layer, the troposphere. The stratosphere lies directly above this region (see chart below).