When the subject of ozone comes up this time of year, we're usually talking about air pollution. Remember, ozone near the ground is the main ingredient in smog. But 10 to 30 miles up, in the stratosphere, ozone absorbs the sun's ultraviolet energy. That's good, because too much ultraviolet radiation reaching the ground can lead to increased rates of skin cancer and other harmful effects.

You've probably heard about the so-called "ozone hole" over the Antarctic. That's what we call a thinning of the ozone layer during late winter and early spring in the stratosphere over that cold continent.

This past February and March, researchers headed north, to the Arctic, to see if something similar happens there. The answer came back "yes" but with a good news / bad news storyline. The good news is that the ozone loss isn't as great over the Arctic as over the Antarctic. The bad news is that most of the world's population lives in the Northern Hemisphere, so any ozone loss over the Arctic is getting a little too close for comfort.