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- ItemIn situ measurements of optical properties at Tinfou (Morocco) during the Saharan Mineral Dust Experiment SAMUM 2006(Milton Park : Taylor & Francis, 2017) Schladitz, A.; Müller, T.; Kaaden, N.; Massling, A.; Kandler, K.; Ebert, M.; Weinbruch, S.; Deutscher, C.; Wiedensohler, A.In situ measurements of optical and physical properties of mineral dust were performed at the outskirts of the Saharan Desert in the framework of the Saharan Mineral Dust Experiment part 1 (SAMUM-1). Goals of the field study were to achieve information on the extent and composition of the dust particle size distribution and the optical properties of dust at the ground. For the particle number size distribution, measured with a DMPS/APS, a size dependent dynamic shape factor was considered. The mean refractive index of the particles in this field study is 1.53–4.1 × 10-3i at 537 nm wavelength and 1.53–3.1 × 10-3i at 637 nm wavelength derived from measurements of scattering and absorption coefficients, as well as the particle size distribution. Whereas the real part of the refractive index is rather constant, the imaginary part varies depending on the mineral dust concentrations. For high dust concentration the single scattering albedo is primarily influenced by iron oxide and is 0.96 ± 0.02 and 0.98 ± 0.01 at 537 nm and 637 nm wavelength, respectively. During low dust concentration the single scattering albedo is more influenced by a soot-type absorber and is 0.89 ± 0.02 and 0.93 ± 0.01 for the same wavelengths.
- ItemTropospheric aerosol scattering and absorption over central Europe: A closure study for the dry particle state(München : European Geopyhsical Union, 2014) Ma, N.; Birmili, W.; Müller, T.; Tuch, T.; Cheng, Y.F.; Xu, W.Y.; Zhao, C.S.; Wiedensohler, A.This work analyses optical properties of the dry tropospheric aerosol measured at the regional Global Atmosphere Watch (GAW) observation site Melpitz in East Germany. For a continuous observation period between 2007 and 2010, we provide representative values of the dry-state scattering coefficient, hemispheric backscattering coefficient, absorption coefficient, single scattering albedo, and scattering Ångström exponent. Besides the direct measurement, the aerosol scattering coefficient was alternatively computed from experimental particle number size distributions using a Mie model. Within pre-defined limits, a closure could be achieved with the direct measurement. The achievement of closure implies that such calculations can be used as a high-level quality control measure for data sets involving multiple instrumentation. All dry-state optical properties show pronounced annual and diurnal variations, which are attributed to the corresponding variations in the regional emission fluxes, the intensity of secondary particle formation, and the mixing layer height. Air mass classification shows that atmospheric stability is a major factor influencing the dry aerosol properties at the GAW station. In the cold season, temperature inversions limit the volume available for atmospheric mixing, so that the dry-state aerosol optical properties near the ground proved quite sensitive to the geographical origin of the air mass. In the warm season, when the atmosphere is usually well-mixed during daytime, considerably less variability was observed for the optical properties between different air masses. This work provides, on the basis of quality-checked in situ measurements, a first step towards a climatological assessment of direct aerosol radiative forcing in the region under study.