Some of us don't have the opportunity to influence national or international policy about caring for the planet. But here's something everybody with a car can do to make a difference: Fill your gas tank only at night.

Why?

Ozone forms when fuel emissions react in the presence of sun and heat. So filling up when the sunlight is less intense reduces the chances of producing ground-level ozone. Emissions that occur early in the day are the most likely to cause ground-level ozone formation because they linger in the air, and the hotter it gets, the more they "bake" in the atmosphere. So wait as late in the day as possible to fill your tank.