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,
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