Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 7 3 2007 10.5194/acpd-7-7843-2007 http://www.atmos-chem-phys-discuss.net/7/7843/2007/ http://www.atmos-chem-phys-discuss.net/7/7843/2007/acpd-7-7843-2007.html http://www.atmos-chem-phys-discuss.net/7/7843/2007/acpd-7-7843-2007.pdf 7843 7905 2007-06-04 Insights into the role of soot aerosols in cirrus cloud formation B. Kärcher bernd.kaercher@dlr.de O. Möhler P. J. DeMott S. Pechtl F. Yu Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre (IPA), Oberpfaffenhofen, Germany Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung (IMK-AAF), Karlsruhe, Germany Department of Atmospheric Science, Colorado State University, Fort Collins, CO, 80523, USA Ruprecht-Karls-Universität Heidelberg, Institut für Umweltphysik (IUP), Heidelberg, Germany State University of New York at Albany (SUNY), Atmospheric Sciences Research Center (ASRC), NY, USA now at: Deutsches Patent- und Markenamt, München, Germany Cirrus cloud formation is believed to be domi\-nated by homogeneous freezing of supercooled liquid aerosols in many instances. Heterogeneous ice nuclei such as mineral dust, metallic, and soot particles, and some crystalline solids within partially soluble aerosols are suspected to modulate cirrus properties. Among those, the role of ubiqui\-tous soot particles is perhaps the least understood. Because aviation is a major source of upper tropospheric soot particles, we put emphasis on ice formation in dispersing aircraft plumes. The effect of aircraft soot on cirrus formation in the absence of contrails is highly complex and depends on a wide array of emission and environmental parameters. We use a microphysical-chemical model predicting the formation of internally mixed, soot-containing particles up to two days after emission, and suggest two principal scenarios, both assuming soot particles to be moderate ice nuclei relative to cirrus formation by homogeneous freezing in the presence of few efficient dust ice nuclei: high concentrations of original soot emissions could slightly increase the number of ice crystals; low concentrations of particles originating from coagulation of emitted soot with background aerosols could lead to a significant reduction in ice crystal number. 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