Most oxygen in the air consists of two joined oxygen atoms, O2. This is the oxygen we breathe. Add another oxygen atom, O3, and you have ozone. Here’s where it gets tricky because there are two kinds of ozone.
Both have the same chemical make up, but ozone high in the Earth’s atmosphere (the ozone layer) protects us from damaging ultraviolet sunlight. Ozone at ground level is a health hazard.
Why is it harmful?
In addition to oxygen, ground-level ozone has pollutants like nitrogen oxides (NOx) and volatile organic compounds (VOCs), which are produced by gas-powered vehicles and lawn equipment, gasoline vapors, household paints and stains, chemical solvents and local industry. Once in the air, they “cook” in the summer heat and affect our health when we breathe it in.