Also, smog can keep children's lungs from developing properly. When ozone levels are high, children should avoid strenuous outdoor activities like soccer and running. Ozone is the main gas that makes up smog. Ozone at the earth's surface is harmful to your health. This harmful ground-level ozone should not be confused with the protective layer of ozone in the upper atmosphere, which screens out the sun's harmful ultraviolet rays.
Most smog is caused by cars, lawnmowers, boats, and other gasoline-burning engines.
Smog is also created by factories and other sources. Harmful ground-level ozone is formed when the chemicals from these sources combine with sunlight. This is why there is more smog on sunny days than on cloudy days. This alert warns the public that the air is harmful to breathe. Because the alert is issued the day before high smog levels are predicted, it also gives you the chance to plan ahead and stop activities that create smog.