Ice nuclei properties within a Saharan Dust Event at the Jungfraujoch

The new portable ice nucleation chamber (PINC) developed by the Institute for Atmo-spheric and Climate Sciences of ETH Zurich was operated during two campaigns PINCII and III at the high alpine research station Jungfraujoch situated at 3580m a.s.l., inMarch and June 2009, respectively. During this time of the year, a high probability of Saharan Dust Events (SDE) at the Jungfraujoch has been observed. We used animpactor with a cutoffsize of 1μm aerodynamic diameter and operated the systemat−31◦C and relative humidities of 127% and 91% with respect to ice and water, re-spectively in order to investigate the contribution of deposition freezing to mixed-phaseclouds and also to look at the number concentration of ice nuclei (IN) during a SDE. The average IN concentration during PINC II was 8 particles per liter whereas duringPINC III, the average number concentration was higher up to 14 particles per liter. TwoSDEs were detected on 15 and 16 June 2009. Our measurements show that the SDEshad IN number concentration up to several hundreds per liter. We found the best corre-lation between the number concentration of the larger particle fraction measured by an optical particle counter and the IN number concentration during a Saharan Dust Event.This correlation factor is higher for particles larger than 0.5 μm meaning that a higherconcentration of larger particles induced higher IN number concentration. No correla-tion could be found between the black carbon mass concentration and the variations inIN number concentration.ISSN:1680-7375ISSN:1680-736