Air pollution also affects materials in the urban environment. Soiling has long been regarded as a problem, originally the result of the smoke from wood or coal fires, but now increasingly the result of fine black soot from diesel exhausts. The acid gases, particularly sulfur dioxide, increase the rate of destruction of building materials. This is most noticeable with calcareous stones, which are the predominant building material of many important historic structures. Metals also suffer from atmospheric acidity. In today's photochemical smog, natural rubbers crack and deteriorate rapidly.
Health problems relating to indoor air pollution are extremely ancient. Anthracosis, or black lung disease, has been found in mummified lung tissue. Recent decades have witnessed a shift from the predominance of concern about outdoor air pollution into a widening interest in indoor air quality.