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- ItemChemical composition and mixing-state of ice residuals sampled within mixed phase clouds(München : European Geopyhsical Union, 2011) Ebert, M.; Worringen, A.; Benker, N.; Mertes, S.; Weingartner, E.; Weinbruch, S.During an intensive campaign at the high alpine research station Jungfraujoch, Switzerland, in February/March 2006 ice particle residuals within mixed-phase clouds were sampled using the Ice-counterflow virtual impactor (Ice-CVI). Size, morphology, chemical composition, mineralogy and mixing state of the ice residual and the interstitial (i.e., non-activated) aerosol particles were analyzed by scanning and transmission electron microscopy. Ice nuclei (IN) were identified from the significant enrichment of particle groups in the ice residual (IR) samples relative to the interstitial aerosol. In terms of number lead-bearing particles are enriched by a factor of approximately 25, complex internal mixtures with silicates or metal oxides as major components by a factor of 11, and mixtures of secondary aerosol and carbonaceous material (C-O-S particles) by a factor of 2. Other particle groups (sulfates, sea salt, Ca-rich particles, external silicates) observed in the ice-residual samples cannot be assigned unambiguously as IN. Between 9 and 24% of all IR are Pb-bearing particles. Pb was found as major component in around 10% of these particles (PbO, PbCl2). In the other particles, Pb was found as some 100 nm sized agglomerates consisting of 3–8 nm sized primary particles (PbS, elemental Pb). C-O-S particles are present in the IR at an abundance of 17–27%. The soot component within these particles is strongly aged. Complex internal mixtures occur in the IR at an abundance of 9–15%. Most IN identified at the Jungfraujoch station are internal mixtures containing anthropogenic components (either as main or minor constituent), and it is concluded that admixture of the anthropogenic component is responsible for the increased IN efficiency within mixed phase clouds. The mixing state appears to be a key parameter for the ice nucleation behaviour that cannot be predicted from the sole knowledge of the main component of an individual particle.
- ItemElectron microscopy of particles collected at Praia, Cape Verde, during the Saharan Mineral Dust Experiment: Particle chemistry, shape, mixing state and complex refractive index(Milton Park : Taylor & Francis, 2017) Kandler, K.; Lieke, K.; Benker, N.; Emmel, C.; Küpper, M.; Müller-Ebert, D.; Ebert, M.; Scheuvens, D.; Schladitz, A.; Schütz, L.; Weinbruch, S.A large field experiment of the Saharan Mineral Dust Experiment (SAMUM) was performed in Praia, Cape Verde, in January and February 2008. The aerosol at Praia is a superposition of mineral dust, sea-salt, sulphates and soot. Particles smaller than 500 nm are mainly mineral dust, mineral dust–sulphate mixtures, sulphates and soot–sulphate mixtures. Particles larger then 2.5μm consist of mineral dust, sea-salt and few mineral dust–sulphate mixtures. A transition range exists in between. The major internal mixtures are mineral dust–sulphate and soot–sulphate. Mineral dust–sea-salt mixtures occur occasionally, mineral dust–soot mixtures were not observed. The aspect ratio was 1.3–1.4 for dry particles smaller than 500 nm and 1.6–1.7 for larger ones. Parameterizations are given for dry and humid state. Although the real part of the refractive index showed low variation (1.55–1.58 at 532 nm), a multi-modal imaginary part was detected as function of particle size, reflecting the complex composition. Soot mainly influences the absorption for wavelengths longer than the haematite absorption edge, whereas for shorter wavelengths dust is dominating. The refractive index of the aerosol depends on the source region of the mineral dust and on the presence/absence of a marine component.
- ItemState of mixing, shape factor, number size distribution, and hygroscopic growth of the Saharan anthropogenic and mineral dust aerosol at Tinfou, Morocco(Milton Park : Taylor & Francis, 2017) Kaaden, N.; Massling, A.; Schladitz, A.; Müller, T.; Kandler, K.; Schütz, L.; Weinzierl, B.; Petzold, A.; Tesche, M.; Leinert, S.; Deutscher, C.; Ebert, M.; Weinbruch, S.; Wiedensohler, A.The Saharan Mineral Dust Experiment (SAMUM) was conducted in May and June 2006 in Tinfou, Morocco. A H-TDMA system and a H-DMA-APS system were used to obtain hygroscopic properties of mineral dust particles at 85% RH. Dynamic shape factors of 1.11, 1.19 and 1.25 were determined for the volume equivalent diameters 720, 840 and 960 nm, respectively. During a dust event, the hydrophobic number fraction of 250 and 350 nm particles increased significantly from 30 and 65% to 53 and 75%, respectively, indicating that mineral dust particles can be as small as 200 nm in diameter. Lognormal functions for mineral dust number size distributions were obtained from total particle number size distributions and fractions of hydrophobic particles. The geometric mean diameter for Saharan dust particles was 715 nm during the dust event and 570 nm for the Saharan background aerosol. Measurements of hygroscopic growth showed that the Saharan aerosol consists of an anthropogenic fraction (predominantly non natural sulphate and carbonaceous particles) and of mineral dust particles. Hygroscopic growth and hysteresis curve measurements of the ‘more’ hygroscopic particle fraction indicated ammonium sulphate as a main component of the anthropogenic aerosol. Particles larger than 720 nm in diameter were completely hydrophobic meaning that mineral dust particles are not hygroscopic.