Das Projekt "Messung gasfoermiger und partikulaerer reaktiver Spurenverbindungen in der Atmoshpaere in der Naehe exponierter und geschaedigter Waelder" wird vom Umweltbundesamt gefördert und von Universität Dortmund, Fachbereich Chemie, Arbeitsgruppe Analytische Chemie durchgeführt. Objective: Compilation of information about concentration variations of gaseous precursors of acids and oxidants and of the corresponding conversion products in the vicinity of exposed and damaged forests. Insight into 'filtration efficiency' of trees with respect to different substances and into chemical processes occurring at surfaces of leaves and needles, respectively. General Information: The planned field project shall be carried out at two sampling sites in the Hochsauerland (State of Nordrhein-Westfalen). It is designed to collect during several periods of tree growth detailed information about the occurrence of such airborne components which due to present knowledge may contribute to the damage of forest trees directly or indirectly. The measurements programme includes gaseous percursors (SO2, NOx, NH3) as well as the corresponding gaseous and particulate conversion products (O3, HNO3, HCl, H2SO4, ammonium salts, other sulfates, nitrates and chlorides). In order to obtain an estimation of the extent of dry deposition of some of the mentioned components two wet-only rain collectors shall be operated in parallel at one of the two sampling sites. One collector is for the collection of 'wet fall', the other one for the collection of 'through fall'. Analysis of the rain samples covers not only the major electrolyte components and some trace heavy metals but also species like SO3, NO2, H2O2 and formaldehyde which play an important role in redox processes in aqueous phase atmospheric chemistry and which might serve as indicators for the occurrence of such reactions on the surfaces of leaves. It is planned to carry out size selective investigations of particulate conversion products as well as analyses of fog and cloud water under suitable meteorological conditions. Cloud water can be collected with a ground based sampler at one of the sites having an elevation of about 800 m or by using an aeroplane.