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 ering the fact that humans can do without food for up to 40 days, without air, how ever, only a few minutes. The first step towards improving the air quality situation is the awareness that a sound environment is as much to be aspired for as the development of new tech nologies improving the standard of living. Technical progress should be judged es pecially by how environmentally benign, clean and noiseless its products are. Of these elements, clean air is of special concern to me. I hope that this book will awaken more interest in this matter and that it will lead to new impulses. Due to the increasing complexity of today's machinery and industrial processes science and technology can no longer do without highly specialized design engineers and opera tors. Environmental processes, however, are highly interdependent and interlinked.