On the isotopic composition of Pb in cloud waters in Central Germany. A source discrimination study

Fifty seven (57) cloud water samples collected in 1 hr intervals during 9 cloud events in 1997 at the summit of the Brocken (altitude 1142 m) in Central Germany were analyzed for their Pb concentrations and isotopic compositions. For comparison, filter dusts of such possible emitters as power plants, cement factories, waste incinerators, cars and others were also studied. Profiles over many hours reveal changes in composition correlated with changes in the origin of the air masses. Five main groups of possible sources of the Pb can be distinguished: most important are (1) the European standard pollution ESP dominating the continent from Germany over France to Scandinavia and (2) industrial Pb (and soot from car exhausts) followed by (3) urban waste incinerators as well as (4) perhaps ores from Norilsk/Siberia, and, somewhat uncertain, (5) ores from Paleozoic European deposits. Local and daily varying anthropogenic emissions of the sources (2-5) cause scatter of the points around the ESP correlation line. In soils all these variations and individual signatures are levelled out so that specific sources of pollution cannot be identified anymore. Geogenic Pb from rocks and soils is the same as that from power plants and cement factories. It is one of the two nominal end components making up the mixture of the ESP. The less radiogenic end component of this mix which must contain Pb from very old deposits is somewhat elusive: none of the large Archaic or Proterozoic deposits could be identified. Most probably numerous sources contribute to this Pb. Pb from leaded gasoline seems to be absent or is hidden under the five components dominating the composition of the Pb in the European environment. This probably reflects phasing out of such gasoline in most European countries. The Pb in the clouds may contain a small component of old Proterozoic or even Archaic Pb, but it can also be modelled with Paleozoic Pb.