Air pollution can cause health problems and can also damage the natural world. So, who are the main contributors to air pollution? In cities, where air pollution is the worst, transportation is one of the major causes. The combustion of gasoline in automobiles, trucks, and airplanes produces a number of major pollutants into the air. Some of these contaminants include carbon monoxide, nitrogen oxides, gaseous hydrocarbons, and lead. When exposed to sunlight, many of these chemicals combine to form additional pollutants that are very harmful. One of these contaminants, nitrogen dioxide, creates smog in the air.