Air pollution in cities

Air quality in cities is the result of a complex interaction between natura l and anthropogenic environmental conditions. Air pollution in cities is a serious environmental problem - especially in the developing countries. The air pollution path of the urban atmosphere consists of emission and transm ission of air pollutants resulting in the ambient air pollution. Each part of the path is influenced by different factors. Emissions from motor traffi c are a very important source group throughout the world. During transmissi on, air pollutants are dispersed, diluted and subjected to photochemical re actions. Ambient air pollution shows temporal and spatial variability. As a n example of the temporal variability of urban air pollutants caused by mot or traffic, typical average annual, weekly and diurnal cycles of NO, NO2, O -3, and O-x, are presented for an official urban air-quality station in Stu ttgart, southern Germany. They are supplemented by weekly and diurnal cycle s of selected percentile values of NO, NO2, and O-3,. Time series of these air pollutants give information on their trends. Results are discussed with regard to air pollution conditions in other cities. Possibilities for the assessment of air pollution in cities are shown. In addition, a qualitative overview of the air quality of the world's megacities is given. (C) 1999 E lsevier Science Ltd. All rights reserved.