Climate Central: Ozone is a bit of a shape-shifting chemical. High in the stratosphere, ozone acts as an ultraviolet-blocking shield around Earth (which is why the ozone hole is such a problem). At ground level, it's a pollutant that can cause serious respiratory problems. And if it finds its way into the troposphere -- the lowest level of the atmosphere -- ozone serves as a potent greenhouse gas that warms the planet.
It ends up in the troposphere through a variety of processes including human pollution. It also...