Untersuchungen zu optischen Eigenschaften atmosphärischer Aerosolpartikel

Anhand von Aerosolen, die während des Lindenberg Aerosol Charakterisierungs Experiment 1998 (LACE 98) gesammelt wurden, wurden der Einfluss und die Bedeutung der Partikelmorphologie, -zusammensetzung und der internen Struktur gemischter Partikel auf die Lichtstreuung und Absorption untersucht. Das Augenmerk lag dabei auf gemischten Partikeln bestehend aus den Komponenten Ruß und Ammoniumsulfat. Die Aerosolpartikel wurden mittels der Einzelpartikelanalyse mit der Hochauflösenden Rasterelektronenmikroskopie und der Transmissionselektronenmikroskopie untersucht. Die Berechnungen der optischen Eigenschaften dieser Partikel wurden mit dem Fortran-Programm DDSCAT durchgeführt. Die wichtigsten Parameter für die optischen Eigenschaften der gemischten Ruß/Sulfat-Partikel sind der Volumenanteil und der Brechungsindex der absorbierenden Ruß-Komponente. Die tatsächliche Anordnung der Rußeinschlüsse und die Partikelmorphologie sind hingegen von untergeordneter Bedeutung. Neben den Eigenschaften eines einzelnen Partikels wurden auch die optischen Eigenschaften für ein gesamtes Aerosol berechnet. Dazu wurden die Partikelzusammensetzung und die Anzahl-Größenverteilung von Aerosolen -gesammelt während des LACE 98-Feldexperiments- verwendet. Den größten Einfluss auf die optischen Aerosoleigenschaften, d.h. die Einfachstreualbedo, haben die Anzahl-Größenverteilung und der interne bzw. externe Mischungszustand und der Rußanteil der gemischten Ruß/Sulfat-Partikel

Optical properties of internally mixed ammonium sulfate and soot particles - a study of individual aerosol particles and ambient aerosol populations

Optical parameters of simulated ambient individual ammonium sulfate and soot-mixed particles were calculated using the discrete-dipole approximation method with different model geometries. Knowledge of the mixing state and the approximation by a suited idealized geometry reduces the errors of the optical properties by ±50% to ±10%. The influence of the soot content and the mixing state on the optical properties of the total aerosol was estimated. For the total aerosol population, the size distribution and the absolute soot content had the largest influence. The exact geometry of the ammonium sulfate and soot-mixed particles can be neglected

Single-particle characterization of ice-nucleating particles and iceparticles residuals sampled by three different techniques

During January/February 2013, at the High Alpine Research Station Jungfraujoch a measurement campaign was carried out, which was centered on atmospheric ice-nucleating particles (INP) and ice particle residuals (IPR). Three different techniques for separation of INP and IPR from the non-ice-active particles are compared. The Ice Selective Inlet (ISI) and the Ice Counterflow Virtual Impactor (Ice-CVI) sample ice particles from mixed phase clouds and allow for the analysis of the residuals. The combination of the Fast Ice Nucleus Chamber (FINCH) and the Ice Nuclei Pumped Counterflow Virtual Impactor (IN-PCVI) provides ice-activating conditions to aerosol particles and extracts the activated INP for analysis.Collected particles were analyzed by scanning electron microscopy and energy-dispersive X-ray microanalysis to determine size, chemical composition and mixing state. All INP/IPR-separating techniques had considerable abundances (median 20 – 70 %) of instrumental contamination artifacts (ISI: Si-O spheres, probably calibration aerosol; Ice-CVI: Al-O particles; FINCH+IN-PCVI: steel particles). Also, potential sampling artifacts (e.g., pure soluble material) occurred with a median abundance of < 20 %. While these could be explained as IPR by ice break-up, for INP their IN-ability pathway is less clear. After removal of the contamination artifacts, silicates and Ca-rich particles, carbonaceous material and metal oxides were the major INP/IPR particle types separated by all three techniques. Soot was a minor contributor. Lead was detected in less than 10 % of the particles, of which the majority were internal mixtures with other particle types. Sea-salt and sulfates were identified by all three methods as INP/IPR. Most samples showed a maximum of the INP/IPR size distribution at 400 nm geometric diameter. In a few cases, a second super-micron maximum was identified. Soot/carbonaceous material and metal oxides were present mainly in the submicron range. ISI and FINCH yielded silicates and Ca-rich particles mainly with diameters above 1 μm, while the Ice-CVI also separated many submicron IPR. As strictly parallel sampling could not be performed, a part of the discrepancies between the different techniques may result from variations in meteorological conditions and subsequent INP/IPR composition. The observed differences in the particle group abundances as well as in the mixing state of INP/IPR express the need for further studies to better understand the influence of the separating techniques on the INP/IPR chemical composition

Inadvertent climate modification due to anthropogenic lead

Aerosol particles can interact with water vapour in the atmosphere, facilitating the condensation of water and the formation of clouds. At temperatures below 273 K, a fraction of atmospheric particles act as sites for ice-crystal formation. Atmospheric ice crystals—which are incorporated into clouds that cover more than a third of the globe1 —are thought to initiate most of the terrestrial precipitation2. Before the switch to unleaded fuel last century, the atmosphere contained substantial quantities of particulate lead; whether this influenced ice-crystal formation is not clear. Here, we combine field observations of ice-crystal residues with laboratory measurements of artificial clouds, to show that anthropogenic lead-containing particles are among the most efficient ice-forming substances commonly found in the atmosphere3. Using a global climate model, we estimate tha