The word “smog” was first used in London during the early 1900s to describe the combination of smoke and fog. Today, the term “smog” is used to describe a mixture of pollutants, primarily made up of ground-level ozone. Ozone can be beneficial or harmful depending on its location. The ozone located high above the surface in the stratosphere protects human health and the environment, but ground-level ozone is responsible for the choking, coughing, and stinging eyes associated with smog.
Smog-forming pollutants come from many sources, such as automobile exhaust, power plants, factories, and many consumer products, including paints, hair spray, charcoal starter fluid, solvents, and even plastic popcorn packaging. In many American cities, at least half of the pollutants come from cars, buses, trucks, and boats. Scientists estimate that about 90 million Americans live in areas with ozone levels above the standards for health safety.