1Department of Physics, University of Kuopio, P.O. Box 1627, 70211 Kuopio, Finland
2Leibniz Institute for Tropospheric Research, Permoserstrasse 15, 04318 Leipzig, Germany
3Division of Atmospheric Sciences, Department of Physical Sciences, P.O. Box 64, 00014, University of Helsinki, Finland
4Federal Environment Agency of Germany (UBA), Paul-Ehrlich-Strasse 29, 63225 Langen Germany
5Finnish Meteorological Institute, Kuopio Unit, P.O. Box 1627, 70210 Kuopio, Finland
6Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
Abstract. In anthropogenically influenced atmospheres, sulphur dioxide (SO2) is the main precursor of gaseous sulphuric acid (H2SO4), which in turn forms new aerosol particles (diameter <10 nm) through nucleation. As a result of socio-economic changes, East Germany has seen a dramatic decrease in anthropogenic SO2 emissions between 1989 and present, as documented by routine air quality measurements in many locations. Using two different data sets of experimental particle number size distributions (3–750 nm) from the research station Melpitz (1996–1997 and 2003–2006) we have attempted to evaluate the possible influence of changing SO2 concentrations on the frequency and intensity of new particle formation (NPF). Between the two periods SO2 concentrations decreased on average by 65%, while the frequency of NPF events dropped by 45%. In addition, the average formation rate of 3 nm particles decreased by 68%. The trends were statistically significant, therefore suggesting a connection between the availability of anthropogenic SO2 and the production of new particle number. A contrasting finding was the increase in the mean growth rate of freshly nucleated particles (+22%), suggesting that particle nucleation and subsequent growth into larger sizes are delineated with respect to their precursor species. Using three basic parameters, the condensation sink for H2SO4, the SO2 concentration, and global radiation intensity, we could define the characteristic range of atmospheric conditions under which particle formation events at the Melpitz site take place or not. While the connection between anthropogenic SO2, H2SO4 and NPF appears very plausible, our analysis yielded no significant evidence whether decreasing SO2 concentrations did affect the production of cloud condensation nuclei (CCN).