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- ItemIn-cloud sulfate addition to single particles resolved with sulfur isotope analysis during HCCT-2010(München : European Geopyhsical Union, 2014) Harris, E.; Sinha, B.; van Pinxteren, D.; Schneider, J.; Poulain, L.; Collett, J.; D'Anna, B.; Fahlbusch, B.; Foley, S.; Fomba, K.W.; George, C.; Gnauk, T.; Henning, S.; Lee, T.; Mertes, S.; Roth, A.; Stratmann, F.; Borrmann, S.; Hoppe, P.; Herrmann, H.In-cloud production of sulfate modifies aerosol size distribution, with important implications for the magnitude of indirect and direct aerosol cooling and the impact of SO2 emissions on the environment. We investigate which sulfate sources dominate the in-cloud addition of sulfate to different particle classes as an air parcel passes through an orographic cloud. Sulfate aerosol, SO2 and H2SO4 were collected upwind, in-cloud and downwind of an orographic cloud for three cloud measurement events during the Hill Cap Cloud Thuringia campaign in autumn 2010 (HCCT-2010). Combined SEM and NanoSIMS analysis of single particles allowed the δ34S of particulate sulfate to be resolved for particle size and type. The most important in-cloud SO2 oxidation pathway at HCCT-2010 was aqueous oxidation catalysed by transition metal ions (TMI catalysis), which was shown with single particle isotope analyses to occur primarily in cloud droplets nucleated on coarse mineral dust. In contrast, direct uptake of H2SO4 (g) and ultrafine particulate were the most important sources modifying fine mineral dust, increasing its hygroscopicity and facilitating activation. Sulfate addition to "mixed" particles (secondary organic and inorganic aerosol) and coated soot was dominated by in-cloud aqueous SO2 oxidation by H2O2 and direct uptake of H2SO4 (g) and ultrafine particle sulfate, depending on particle size mode and time of day. These results provide new insight into in-cloud sulfate production mechanisms, and show the importance of single particle measurements and models to accurately assess the environmental effects of cloud processing.
- ItemInfluence of cloud processing on CCN activation behaviour in the Thuringian Forest, Germany during HCCT-2010(München : European Geopyhsical Union, 2014) Henning, S.; Dieckmann, K.; Ignatius, K.; Schäfer, M.; Zedler, P.; Harris, E.; Sinha, B.; van Pinxteren, D.; Mertes, S.; Birmili, W.; Merkel, M.; Wu, Z.; Wiedensohler, A.; Wex, H.; Herrmann, H.; Stratmann, F.Within the framework of the "Hill Cap Cloud Thuringia 2010" (HCCT-2010) international cloud experiment, the influence of cloud processing on the activation properties of ambient aerosol particles was investigated. Particles were probed upwind and downwind of an orographic cap cloud on Mt Schmücke, which is part of a large mountain ridge in Thuringia, Germany. The activation properties of the particles were investigated by means of size-segregated cloud condensation nuclei (CCN) measurements at 3 to 4 different supersaturations. The observed CCN spectra together with the total particle spectra were used to calculate the hygroscopicity parameter κ for the upwind and downwind stations. The upwind and downwind critical diameters and κ values were then compared for defined cloud events (FCE) and non-cloud events (NCE). Cloud processing was found to increase the hygroscopicity of the aerosol particles significantly, with an average increase in κ of 50%. Mass spectrometry analysis and isotopic analysis of the particles suggest that the observed increase in the hygroscopicity of the cloud-processed particles is due to an enrichment of sulfate and possibly also nitrate in the particle phase.
- ItemComprehensive assessment of meteorological conditions and airflow connectivity during HCCT-2010(München : European Geopyhsical Union, 2014) Tilgner, A.; Schöne, L.; Bräuer, P.; van Pinxteren, D.; Hoffmann, E.; Spindler, G.; Styler, S.A.; Mertes, S.; Birmili, W.; Otto, R.; Merkel, M.; Weinhold, K.; Wiedensohler, A.; Deneke, H.; Schrödner, R.; Wolke, R.; Schneider, J.; Haunold, W.; Engel, A.; Wéber, A.; Herrmann, H.This study presents a comprehensive assessment of the meteorological conditions and atmospheric flow during the Lagrangian-type "Hill Cap Cloud Thuringia 2010" experiment (HCCT-2010), which was performed in September and October 2010 at Mt. Schmücke in the Thuringian Forest, Germany and which used observations at three measurement sites (upwind, in-cloud, and downwind) to study physical and chemical aerosol–cloud interactions. A Lagrangian-type hill cap cloud experiment requires not only suitable cloud conditions but also connected airflow conditions (i.e. representative air masses at the different measurement sites). The primary goal of the present study was to identify time periods during the 6-week duration of the experiment in which these conditions were fulfilled and therefore which are suitable for use in further data examinations. The following topics were studied in detail: (i) the general synoptic weather situations, including the mesoscale flow conditions, (ii) local meteorological conditions and (iii) local flow conditions. The latter were investigated by means of statistical analyses using best-available quasi-inert tracers, SF6 tracer experiments in the experiment area, and regional modelling. This study represents the first application of comprehensive analyses using statistical measures such as the coefficient of divergence (COD) and the cross-correlation in the context of a Lagrangian-type hill cap cloud experiment. This comprehensive examination of local flow connectivity yielded a total of 14 full-cloud events (FCEs), which are defined as periods during which all connected flow and cloud criteria for a suitable Lagrangian-type experiment were fulfilled, and 15 non-cloud events (NCEs), which are defined as periods with connected flow but no cloud at the summit site, and which can be used as reference cases. The overall evaluation of the identified FCEs provides the basis for subsequent investigations of the measured chemical and physical data during HCCT-2010 (see https://www.atmos-chem-phys.net/special_issue287.html).