Manual on Urban Air Quality Management

Deteriorating air quality from the presence of unpleasant, toxic, or corrosive gases, dust, or grit, and the release of waste heat from industry or private dwellings is a growing problem in many parts of the world, particularly in large cities and other densely populated, highly industrialized areas. Smaller sources also make significant contributions to the general pollution of the atmosphere and the total effect may be experienced over wide areas. The natural cleansing processes of the atmosphere may normally be expected to reduce the level of pollution, but in some situations these natural processes are becoming dangerously overloaded.