Atmospheric air in industrial cities of the USSR contains high concentrations of a wide range of toxicants, including benz(a)pyrene and heavy metals. To assess the impact of polluted air on public health a 5-level scale of health effects proposed by WHO experts and modified by the author was used. The "extremely hazardous" level of pollution characteristic of cities with metallurgic and chemical industries is described most specifically. An ecological taxonomy for cities of various industrial types is worked out. The latter is based on the results of interrelated studies of environmental pollution in cities and changes in public health characteristics.