Air pollution from coal smoke brings to mind the grimy cities of the 19th century and the evils accompanying the industrial revolution. It was natural to assume that the polluted air was responsible for many instances of pulmonary disease and that the removal of coal smoke would greatly improve the health of the residents of cities with a heavy burden of air pollution. A remarkable reduction in air pollution from coal smoke has occurred in the past few decades. This improvement was related partly to the substitution of natural gas and oil for coal, and partly to government regulations limiting . . .