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Abstract

The condensational growth of aerosol particles and the formation of fresh, nanometer-sized particles depend primarily upon the presence of H2SO4. Atmospheric ions produced by cosmic rays can initialize the formation of cluster ions, which subsequently may grow by mutual coagulation and condensation of H2SO4 and H2O. In the present work, measurements of the H2SO4 precursor SO2 and atmospheric cluster ions were performed using an ion trap chemical ionisation mass spectrometer(IT-CIMS)and a quadrupole mass spectrometer(QMS). The ion molecule reaction to determine atmospheric SO2 was calibrated isotopically. So problems arising from wall losses and ion hydration are circumvented in an elegant manner. The modifed IT-CIMS was integrated into the German research aircraft Falcon and successfully employed during the international aircraft campaign ITOP(International Transport of Ozone and Precursors). During another aircraft campaign, CONTRACE(Convective Transport of Trace Gases), the QMS aboard the Falcon detected atmospheric cluster ions. Significant correlations between detected small particles and clusterions were found. During ITOP a plume of strongly enhanced SO2 concentrations in the lowermost stratosphere was observed, that originated from North America by overshooting deep convection. Model simulations based on the SO2 data indicate that the measured particles can be explained by binary nucleation and growth (condensation and coagulation) of H2SO4 and H2O.