Photochemical oxidants are secondary air pollutants formed under the influence of sunlight by complex photochemical reactions in air which contains nitrogen oxides and reactive hydrocarbons as precursors. The most adverse components formed by photochemical reactions in polluted air are ozone (0 ) 3 and peroxyacetyl nitrate (PAN), among many other products such as aldehydes, ketones, organic and inorganic acids, nitrates, sulfates etc. An analysis and evaluation of the available knowledge has been used to characterize the relationships among emissions, ambient air concentrations, and effects, and to identify the important controlling influences on the formation and effects of photochemical oxidants. The biological activity of photochemical oxidants was first clearly manifested during the early 1940's, when vegetation injury was observed in the Los Angeles Basin in the United States. Since that time, as a consequence of the increasing emissions of photochemical oxidant precursors, the photochemical oxidants have become the most important air pollutants in North America. In other parts of the world, for example South and Central America, Asia, and Australia, photo chemical oxidants threaten vegetation, particularly the economic and ecological performance of plant life. According to my knowledge, the first observations of ozone and PAN injury to vegetation in Europe were made by Dr. Ellis F. Darley (Statewide Air Pollution Research Center, University of California, Riverside, California) during a study visit (1963/64) to the Federal Republic of Germany."

Emissions of gaseous air pollutants have increased in the last years in spite of increased controls and concern for air quality. Predictions of future development also indicate that a further increase in emissions must be expected. From an extensive analysis of fuel use in conventional power plants in industry and for domestic heating, Brocke and Schade (1971) and Schade (1975) predict that sulfur dioxide (S02) emissions in the Federal Republic of Germany will increase from '3. 5 million t in 1969, over 4. 2 million t in 1973, to 4. 6 million t in 1980. Rasch (1971) predicts that emission of hydrogen chloride (HCI) from burning of wastes will increase from a present 8000 t/year to about 100000 t in 1980. Emission of gaseous fluoride compounds, in North Rhine Westphalia alone, are expected to increase from 7500 t in 1969 to 8800 t in 1985 (MAGS, 1972). Similar predic tions have also been made in the USA (Heggestadt and Heck, 1971). A doubling of S02 emissions from oil and particularly coal-fired power plants is expected between 1960 and 1980 (Wood, 1968; Lewis et aI. , 1974). When it is considered that total control of air pollutants is technically and especially economically impossible, it is important that, in the future, emissions are controlled within a technical and economic framework to such an extent that ambient pollutant concentrations near the ground present no hazard to man or his environment (BImSchG, 1974).

Im Rahmen dieser Studie werden aus naturwissenschaftlich-medizinischer, soziologischer, oekonomischer, juristischer und philosophischer Perspektive Notwendigkeit, Realisierbarkeit und Konsequenzen von Umweltstandards fur kombinierte Expositionen untersucht. Auf Expositionen des Menschen - dabei besonders deren karzinogene sowie genotoxische Wirkungen - sowie Expositionen einer Auswahl von Pflanzen, anhand derer die pragmatisch dringlichsten Fragen beantwortet werden, ist das Hauptaugenmerk der Studie gerichtet. Auf der Grundlage einer auf Wirkungsmechanismen basierenden Kategorisierung kombinierter Expositionen werden Kriterien erarbeitet, die trotz der Komplexitat der einzelnen Wirkungszusammenhange eine Grenzwertsetzung zur Erhaltung bzw. Erreichung konkreter Umweltqualtitatsziele ermoeglicht.