The waste gases that escape from factories or power plants running on fossil fuels typically contain a variety of pollutants, including carbon monoxide, particulates, nitrogen oxides, and sulfur. The first of these pollutants, carbon monoxide, tends to dispense rapidly once it is released to the atmosphere and seldom poses a serious threat to human health or the environment. The same cannot be said of the last three categories of pollutants, all of which pose a threat to the well-being of plants, humans, and other animals.

During the 1960s, humans became increasingly aware of the range of hazards, posed by pollutants escaping from smokestacks. One of the most common events of the time was for residents in the area immediately adjacent to a factory or plant to find their homes and cars covered with fine dust from time to time. They soon learned that the dust was...