Saharan dust events at the Jungfraujoch: detection by wavelength dependence of the single scattering albedo and first climatology analysis

[摘要] Scattering and absorption coefficients have been measured continuously atseveral wavelengths since March 2001 at the high altitude site Jungfraujoch(3580ma.s.l.). From these data, the wavelength dependences of theÅngström exponent and particularly of the single scattering albedo aredetermined. While the exponent of the single scattering albedo usuallyincreases with wavelength, it decreases with wavelength during Saharan dustevents (SDE) due to the greater size of the mineral aerosol particles andtheir different chemical composition. This change in the sign of the singlescattering exponent turns out to be a sensitive means for detecting Saharandust events. The occurrence of SDE detected by this new method was confirmedby visual inspection of filter colors and by studying long-rangeback-trajectories. An examination of SDE over a 22-month period shows thatSDE are more frequent during the March-June period as well as during Octoberand November. The trajectory analysis indicated a mean traveling time of96.5h, with the most important source countries situated in thenorthern and north-western part of the Saharan desert. Most of the SDE donot lead to a detectable increase of the 48-h total suspended particulatematter (TSP) concentration at the Jungfraujoch. During Saharan dust events,the average contribution of this dust to hourly TSP at the Jungfraujoch is16µg/m³, which corresponds to an annual mean of 0.8µg/m³ or 24% of TSP.

[学科分类] 大气科学