9. Summary

The higher regions of the Alps offer in Europe unique possibilities for the investigation of aerosol transport and transfer processes from aerosol to precipitation. In winter, an inversion layer separates this region from aerosol sources in the neighbouring valleys, so the horizontal long-range transport of aerosols can be observed. From spring to autumn ascending air masses cause aerosol transport because of convection.

During precipitation events high-altitude places e.g. the High Alpine Research Station Jungfraujoch are surrounded by clouds, the phases which are participating at the scavenging processes cloud droplets, snow-flakes and aerosol can be determined simultaneously side by side. Further scavenging on the way from the lower edge of the cloud to the ground don’t take place here.

Within the scope of the considered work new-fall snow and aerosol were collected during three intensive field campaigns of the Paul Scherrer Institute, Villigen, Switzerland at the the High Alpine Research Station Jungfraujoch. HNO3, NH3 and their salts were collected in the aerosol with an annular denuder system (ADS), that allowed the separate detection of the gaseous and particulate portion of this nitrogen compounds.

The suitability of this collector, whose construction was modified by parallel sampling with filter packs during field campaigns in Erfurt, Schwerin and Eilsum of the Institute for Inorganic and Applied Chemistry of the University of Hamburg, Department of Applied Analysis (Institut für Anorganische und Angewandte Chemie der Universität Hamburg, Abt. Angewandte Analytik), the reproducability was tested by parallel operation of two nearly identical ADS on the ground of the Paul Scherrer Institut.

The meteorological setting at the Jungfraujoch with temperatures below 0° C and an average atmospheric pressure of 650 mbar could not be taken into consideration in the preliminary experiments. In comparison with a filter pack, operated by collaborators of the PS it has shown that in 1992 obviously a leak in the low-pressure part of ADS has lead to smaller results in the aerosol data. The NaF used for HNO3-separation contaminated the PTFE-Backup filter so the sodium-date could be used only restricted.

The ADS turned out to be suited for sampling with a temporal resolution of 12 hours. Depending on aerosol load a higher temporal resolution can be chosen. Towards the intrusion of new-fallen snow the ADS is just as sensitive as the used filter pack. On an average over the three field campaigns 126 ng/m³ HNO3, 73 ng/m³ NH3, 134 ng/m³ NH4+, 80 ng/m³ NO3- and 502 ng/m³ SO42- were found. In spring the concentrations were higher by the factor 2 to 8 than in autumn.

The classification of the data sets to the corresponding wind direction resulted from the high altitude wheather charts of the Schweizer Meteorolische Anstalt in Zürich. Local wind data could not be used due to the location of Jungfraujoch, which allows only two directions. In spring 1992 the concentrations were the highest by wind from N/NE, in autumn 1993 no wind direction was preferred.

Aerosol was collected for the analysis of heavy metals on PTFE-filters by a low-volume sampler. After processing of the samples by a microwave-high-pressure digestion, between 11 and 21 element contents were determined by AAS and ICP-MS. After calculation of environment factors with Al as reference element this elements were devided in two groups of geogene resp. anthropogenic origin. For example Cd, Cu and Pb belong to the anthropogenic elements. The difference between spring- and autumn – mean values was smaller as the ones for the water-soluble aerosol-components. The classification of the samples with respect to the wind directions showed a different behaviour for samples of geogene and anthropogene origin with different concentration maxima depending on wind direction. A comparison of the Na-, K-, Ca- and Mg-data from ADS and heavy metal-samples showed no correspondence. The salts were only partially solved in aqueous solution, the high-pressure digestion with HF lead to the loss of Ca and Mg.

Fresh-fallen snow was also investigated for heavy metals. The samples were reduced by evaporation and digested. The enrichment allowd the analytical determination of 19 elements. The enrichment factors related to the Al were lower than in aerosol. For a comparison with literature data of crustal elements processing of the samples must be considered. The transfer of aerosol particles happens on several ways. Mineral particles act as ice condensation nuclei. By the growing of the crystals cloud droplets were included due to riming. Small particles can be deposited on the crystals. A linear relationship between aerosol- and snow-concentration is showd approximately by some crustal elements like Fe and Ca.

It was showed in this paper that the discontinous sampling of aerosols with PTFE filters and denuder systems was well suited for the determination of gaseous and particulate species in a high-alpine region with a temporary resolution of 12 to 24 hours. The investigation of transfer processes can be made thereby well on higher regions of the Alps. But the samplers need better protection against intruding of snow and rime, because the corresponding sampling of aerosols and fresh-falle snow during precipitation events is important for the study of atmospheric scavenging processes. The investigation of transport- and scavenging processes can be supplemented by the interpretation of heavy metal data. Further research is needed for the conclusion from precipitation data, e.g. from fin or ice cores, to the corresponding aerosol composition at the time of precipitation formation.