According to the EPA ozone produced from Smog is unhealthy, while ozone used commercially and in the ozone layer is safe and healthy. What makes the difference?
The answer is simple, and yet complicated at the same time. Ozone produced naturally is produced from nature the way God intended. However, ozone produced from smog is a chemical reaction and a by-produce of pollution. When ozone is produced from smog, ozone is not produced directly, but indirectly from an undesirable chemical reaction that begins a difficult to stop cycle.
See image above. NO2, and VOC’s are produced as part of pollution, or smog. This NO2 is broken down to NO and O. The extra O can combine with atmospheric O2 to form O3. However, due to the short half life of O3, it will quickly break down into O2 and O to form NO2 again. And the cycle repeats itself. This is an unhealthy pollution cycle that is difficult to break.
When ozone is produced naturally or commercially it is produced from oxygen and quickly breaks back down into oxygen. However, when ozone is produced from the chemical reaction of the smog cycle, this is not the case.
Ozone is commonly measured in air along with NO2 as these are the easy to measure pollution levels. Also, it is ozone that is an unhealthy gas that causes safety issues at the lowest levels in the air.
It is important to remember that when ozone is produced from smog, this is bad ozone. However there is still good ozone that has useful application in food processing, drinking water treatment and the ozone layer.