Time study of trace elements and major ions during two cloud events at the Mt. Brocken

Cloud water investigations have been performed at the highest elevation of Central Germany in 1997. Results of extensive trace element measurements are presented. Besides conductivity, pH, liquid water content and major ions the data set includes 49 minor and trace elements. Estimation of crustal enrichment factors (EFs) provides an indication of the anthropogenic contributions to the cloud water concentrations. The variation of cloud composition with time has been illustrated for two selected events with different air mass origins. The chemical composition of the cloud condensation nuclei on which the droplets grow mainly determines the cloud water chemistry. For a cloud event in June 1997 the concentrations of the crustally derived elements Si, Al, Fe, Ti, Ce, La and Nd follow each other closely. The fact that SO42−, NO3− and NH4+ are only moderately correlated with the particular pollutants with high enrichment factors such as Cd, Sb, Pb, Zn, Cu, As, Bi, Sn, Mo, Ni, Tl and V indicates that their source regions are more widespread. During an event in October 1997 the time trends for most minor and trace elements follow rather closely those for the major ions NH4+, SO42− and NO3−. Back trajectories show that the transport from continental and marine European sources was the likely cause of the sample concentrations. EFs of trace elements in cloud water samples during the June and October event show a strong correlation with those obtained for urban particulate matter. Although both events are influenced by air masses of different origin, there is a good agreement between the EF signatures.