The hydrocarbons that produce ozone come from a variety of sources - from vapors at the gas pump to the baking of yeast-raised bread.
But environmental officials say there isn't much the average person can do to stop the formation of ozone. The best bets are driving less, and getting ready for a possible new round of pollution controls at gas stations or in new cars.
"It's too early at this point to start looking at the very, very minute amounts that, when taken as a whole, contribute to the ozone problem," said Joseph Otis Minott, executive director of the Delaware Valley Clean Air Council. "Pennsylvania has a long ways to go toward controlling very, very large amounts."