Ozone is the main component of smog. It can cause shortness of breath and make respiratory problems worse especially for the young, the elderly and those who already have breathing problems.
Ozone is particularly troublesome on hot sunny days.
It's formed when volatile organic compounds from fuel vapors and nitrogen oxides from industrial emissions chemically react with the hot summer sun. Ozone is also the most difficult air pollutant to control. But there are things we can all do to help. On steamy sunny days, try to carpool with neighbors and coworkers. Postpone mowing your yard.