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Summary At the present time the formation processes of clouds and precipitation are not totally understood. Because cloud- and raindroplets
are major sinks for chemical species in the atmosphere it is important to understand the physical and the chemical processes
which occur during precipitation. The development of models is hindered by the scarcity of information about the scavenging
of gases or aerosol particles by raindrops of different sizes. These processes can only be investigated by field experiments
using microanalytical methods and analysing single raindrops as well as size-classified raindrop samples. Raindrops were collected
according to their size by freezing them in liquid nitrogen (“Guttalgor” method). Sample volumes of the smallest raindrop
sizes (radius <200μm) were usually smaller than 2 μL. The analysis of microvolumina in the size range of μL down to pL required
the development of methods designed especially for this purpose. Analysis of rain samples was carried out by capillary electrophoresis.
Organic acids were determined using a new electrolyte system for indirect detection. With this system it was possible to determine
monocarboxylic acids (C1−C4) dicarboxylic acids (C2−C4, C9) and inorganic anions (Cl−, NO3
−, SO4
2−) in the rain samples. Carbonyl compounds were analysed after derivatisation with dansylhydrazine using direct UV-detection.
The system allows the identification of aliphatic carbonyl compounds (C1−C3, C5) as well as benzaldehyde. It was found that carbonyl compounds and carboxylic acids showed concentration maxima at different
raindrop radii. These concentration maxima are a consequence of particle scavenging. By using the results of a former experiment
we concluded that the two species are located on different aerosol particle sizes. Reasons for the different particle sizes
where these species are located are discussed.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
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