Good Ozone, Bad Ozone

In some situations ozone can react with and neutralize other pollutants, which is why ozone is intentionally created to purify water, and why some companies even sell ozone generators as air purifiers. The scientific consensus, however, is that ozone should never be generated in air that people might breathe (see Newsbrief: California Limits Ozone-Generating Air Purifiers).

That which is harmful up close can be essential at the proper distance; for ozone, this distance is between 10 and 20 miles (16–32 km) overhead, in the stratosphere. That’s where the “ozone layer” intercepts harmful ultraviolet (UV) rays from the sun, protecting all forms of life from cell damage, such as (in humans) sunburns and skin cancer. The maximum concentration of ozone in that layer is less than ten parts per million (ppm), but that’s 100 times more than the level that would trigger a smog alert on the ground.