Clearly, despite effective abatement measures, atmospheric Pb will continue to be dominated by anthropogenic mobilization. The influence from long-range transport can be expected to decrease with the effectiveness of abatement programmes in neighbouring countries of the region.
Abstract. Yearly averages of geomagnetic activity indices Ap for the years 1967±1984 are compared to the respective averages of m 2 Á f s , where v is the solar wind velocity and f s is the southward interplanetary magnetic ®eld (IMF) component. The correlation of both quantities is known to be rather good. Comparing the averages of Ap with m 2 and f s separately we ®nd that, during the declining phase of the solar cycle, m 2 and during the ascending phase f s have more in¯uence on Ap. According to this observation (using Fourier spectral analysis) the semiannual and 27 days, Ap variations for the years 1932±1993 were analysed separately for years before and after sunspot minima. Only those time-intervals before sunspot minima with a signi®cant 27-day recurrent period of the IMF sector structure and those intervals after sunspot minima with a signi®cant 28±28.5-day recurrent period of the sector structure were used. The averaged spectra of the two Ap data sets clearly show a period of 27 days before and a period of 28±29 days after sunspot minimum. Moreover,
ZusammenfassungDie Bestimmung der mittleren Verweilzeit yon Aerosolen aus dem gest6rten radioaktiven Gleichgewicht der angelagerten RaD-und RaE-Aktivit/iten wird er6rtert. Die angewandte experimentelle Methode wird ausfiihrlich behandelt, insbesondere die Aufarbeitung des zum Auffangen der Aerosole beniitzten Glasfaserfilters und die chemische Abtrennung yon Wismut und Blei. Dabei wird Wert gelegt auf die Verwendung der mitabgeschiedenen Thoron-Folgeprodukte als radioaktive Tracer bei der RaD-RaE-Analyse.Einige Megergebnisse werden mitgeteilt. Auf die Bedeutung yon gleichzeitigen ~176 der Filterproben ffir die Absch/itzung des ,,stratosph/irischen" Ra D-Anteils wird hingewiesen.
Summary Contribution to the Determination of the Averages Delay-Time of Natural Aerosols; Method and First ResultsThe determination of the average delay-time of aerosols from the disturbed equilibrium of radioactivity of the attached RaD and RaE activities is reported. The experimental method used is thoroughly discussed, especially the treatment of the glass fibre filter which is used for the collection of the aerosols and the chemical separation of bismuth and lead. In this process much care is dedicated to the use of the precipitated daughter-products of thoron as radioactive tracers in the RaD-RaE-analysis.Some results of the measurements are communicated. The authors stress the importance of simultaneous 9~ measurements of the filter samples for the estimation of the stratospheric RaD portion.
H. SCHREIBER et al.
R6sum6Contribution /t la d6termination de la dur6e moyenne du maintien des a6rosols naturels; m6thode et premiers resultsOn discute ici comment il est possible de d6terminer la dur6e moyennc durant laquelle les a6rosolcs se maintiennent en suspension en utilisant la rupture de l%quilibre radioactif r~sultant des activit~s de RaD et RaE d6pos6s. On d6crit en d6tail la m6thode exp6rimentale utilis~e, en particulier la pr6paration du filtre de fibres de verre destin~ h retenir les a6rosoles ainsi que la s6paration chimique du bismuth et du plomb. On fait ici grand cas de l'utilisation des sous-produits du thorium d~posfis 6galement et qui sont consid~r6s comme traceurs radioactifs dans l'analyse de RaD et de RaE. On communique aussi quelques r6sultats d'analyses. On rend enfin le lecteur attentif & la signification de la mesure du 9~ d6pos6 sur le filtre pour l'estimation de la part "stratosph~rique" de RaD.
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