This happens when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources chemically react in the presence of sunlight. Ozone at ground level is a harmful air pollutant, because of its effects on people and the environment, and it is the main ingredient in “smog."
The word smog is created from the words "smoke" and "fog". It contains chemicals such carbon monoxide, sulfur dioxide, and various nitrogen oxides. It is created mostly from the burning of fossil fuels, such as gasoline, which is used commonly as fuel components for many different vehicles. Having known that such chemicals are found in exhaust fumes from cars, it is safe to say that the answer could either be smoke, or carbon dioxide(depending on teacher expectations).
