Air quality and air pollution control are tasks of international concern as, for one, air pollutants do not refrain from crossing borders and, for another, industrial plants and motor vehicles which emit air pollutants are in widespread use today. In a number of the world's expanding cities smog situations are a frequent occurrence due to the number and emission-intensity of air pollution sources. Polluted air causes annoy ances and can, when it occurs in high concentrations in these cities, constitute a seri ous health hazard. How important clean air is to life becomes apparent when consid...