Urban air pollution problems have existed for centuries and result from the burning of wood, vegetation, coal, natural gas, oil, gasoline, kerosene, diesel, waste, and chemicals. Two general types of urban-scale pollution were identified in the twentieth century: London-type smog and photochemical smog. The former results from the burning of coal and other raw materials in the presence of a fog or strong inversion, and the latter results from the emission of hydrocarbons and oxides of nitrogen in the presence of sunlight. In most places, urban pollution consists of a combination of the two. In this chapter, gas-phase urban air pollution is discussed in terms of its early history, early regulation, and chemistry.

HISTORY AND EARLY REGULATION OF URBAN AIR POLLUTION

Before the twentieth century, air pollution was not treated as a science but as a regulatory or legal problem. Because regulations were often weak or not enforced and health problems associated with air pollution were not well understood, pollution problems were rarely mitigated. In this section, a brief history of air pollution and its regulation until the 1940s is discussed.

Before 1200

In ancient Greece, town leaders were responsible for keeping sources of odors outside of town. In ancient Rome, air pollution resulted in civil lawsuits. The Roman poet Horace noted thousands of wood-burning fires (Hughes, 1994) and the blackening of buildings (Brimblecombe, 1999). Air pollution events caused by emissions under strong inversions in Rome were called heavy heavens (Hughes, 1994).