Smog (Air Pollution)

SMOG (AIR POLLUTION)

"Smog" is a popular term used to describe polluted air. It was originally used as an abbreviation of the combination of coal smoke and fog that, along with sulfur dioxide vapor, characterized polluted air in London and other British cities in the 1950s. The term came into more widespread use as a summary description for the quite different pollution mixture of ozone (O₃) and other photochemical oxidants (e.g., hydrogen peroxide, hydroxgl radical peroxy acetylnitrate) that characterized the air pollution in Southern California beginning in the 1950s, and in many other urban areas in the United States in the decades that followed. In the United Kingdom, the smog was black and acidic, while the smog in California was lighter in color and more highly oxidizing.

The black smoke in Britain was heavier in the winter months, and was most closely associated with its reducing power as a chemical (i.e., antioxidant), and with excess mortality, from chronic bronchitis and respiratory symptoms. By contrast, the California mixture was worse in the summer, and was characterized in terms of its oxidizing power. It attacked rubber and chemical polymers, and was associated with eye irritation, reduced lung function, and impaired athletic performance. In both mixtures there were fine particles that caused light to scatter and reduced the range of visibility.

In the United States, United Kingdom, and other economically developed countries in the twentieth century, the black smoke components of past pollution have largely been controlled, and the residual pollution problem is most closely related to the concentrations of light-scattering fine particles and ozone that form in the atmosphere from gaseous precursors (ie, pollutant chemicals whose reaction products have low vapor pressures and condense into fine particles). Such pollution mixtures are generally referred to as smog. While generally present at lower concentrations than in the past, these mixtures are still associated with excess cardiopulmonary mortality, morbidity, and physiologic function deficits. Attribution of the effects to specific components of the pollution mixture remains controversial, and further chemical characterization and health-effects research is now underway to resolve the remaining uncertainties.

Morton Lippmann

(see also: Airborne Particles; Air Quality Index; Ambient Air Quality [Air Pollution]; Automotive Emissions; Carbon Monoxide; Clean Air Act; Environmental Determinants of Health; Fossil Fuels; Fuel Additives; Inhalable Particles [Sulfates] )