ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-2465-2004 Saharan dust events at the Jungfraujoch: detection by wavelength dependence of the single scattering albedo and first climatology analysis Collaud Coen M. 1 Weingartner E. 2 Schaub D. 3 Hueglin C. 3 Corrigan C. 2 4 Henning S. 2 5 Schwikowski M. 6 Baltensperger U. 2 MeteoSwiss, Aerological Station, Les Invuardes, CH-1530 Payerne, Switzerland Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland Swiss Federal Laboratories for Materials Testing and Research, Überlandstrasse 129, CH-8600 Dübendorf, Switzerland University of California, San Diego, 9500 Gilman Drive, MC 0221, La Jolla, CA 92093-0221, USA Chemical Institute, Copenhagen University, DK-2100 Copenhagen, Denmark Laboratory of Radio- and Environmental Chemistry, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland 08 12 2004 4 11/12 2465 2480 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/4/2465/2004/acp-4-2465-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/2465/2004/acp-4-2465-2004.pdf

Scattering and absorption coefficients have been measured continuously at several wavelengths since March 2001 at the high altitude site Jungfraujoch (3580ma.s.l.). From these data, the wavelength dependences of the &#197;ngstr&#246;m exponent and particularly of the single scattering albedo are determined. While the exponent of the single scattering albedo usually increases with wavelength, it decreases with wavelength during Saharan dust events (SDE) due to the greater size of the mineral aerosol particles and their different chemical composition. This change in the sign of the single scattering exponent turns out to be a sensitive means for detecting Saharan dust events. The occurrence of SDE detected by this new method was confirmed by visual inspection of filter colors and by studying long-range back-trajectories. An examination of SDE over a 22-month period shows that SDE are more frequent during the March-June period as well as during October and November. The trajectory analysis indicated a mean traveling time of 96.5h, with the most important source countries situated in the northern and north-western part of the Saharan desert. Most of the SDE do not lead to a detectable increase of the 48-h total suspended particulate matter (TSP) concentration at the Jungfraujoch. During Saharan dust events, the average contribution of this dust to hourly TSP at the Jungfraujoch is 16&micro;g/m<sup>3</sup>, which corresponds to an annual mean of 0.8&micro;g/m<sup>3</sup> or 24% of TSP.