that thousands more died of health complications from the event in the next several months
(Figure22.1).
Figure 22.1: A film crew recreates London smog in the Victorian Era. ( 2 )A different type of air pollution became a problem in Southern California after World War II.
Although there was no coal smoke, cars and abundant sunshine producedphotochemical
smog. This smog is the result of a chemical reaction between some of the molecules in auto
exhaust or oil refinery emissions, and sunshine. Photochemical smog consists of more than
100 compounds, most importantly ozone.
In the United States, these events led to the passage of the Clean Air Act in 1970. The
act now regulates 189 pollutants. The six most important pollutants are ozone, particu-
late matter, sulfur dioxide, nitrogen dioxide, carbon monoxide, and the heavy metal lead.
Other important regulated pollutants include benzene, perchloroethylene, methylene chlo-
ride, dioxin, asbestos, toluene, and metals such as cadmium, mercury, chromium, and lead