Talk about an identity crisis! Consider the case of the gas "ozone". Sometimes it's hailed as necessary for life on earth, while at other times it's portrayed as a pollutant that we need to get rid of!

There's some truth to both identities - it just depends on where the ozone is. Most is in the stratosphere, the layer of air 10 to 30 miles up. Ozone up there is good. It absorbs harmful ultraviolet radiation from the sun, preventing that radiation from reaching the surface where it can cause sunburns and skin cancer.

But ozone at ground-level is the primary ingredient in smog. Down here, ozone is a pollutant that's unhealthy to breathe and harmful to plants and some materials. Here's a catchy way to remember ozone's double-life: "Ozone is good up high, but bad nearby".

The warm season is the time when ground-level ozone pollution is at its worst. So this is a good week to get our ozone facts in order.