People who already have lung disease and people who exercise outdoors are especially at risk. Children are affected the most by high smog levels. This is because children spend more time outdoors and have narrower airways than adults. 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.