Submitted on May 9, 2006
Accepted on August 16, 2006
Solid Ammonium Sulfate Aerosols as Ice Nuclei: A Pathway for Cirrus Cloud Formation
J. P. D. Abbatt 1*,
S. Benz 2,
D. J. Cziczo 3,
Z. Kanji 1*,
U. Lohmann 3,
O. Möhler 2
1 Department of Chemistry, University of Toronto, Toronto, ON M5S 3H6, Canada.
2 Institute for Meteorology and Climate Research (IMK-AAF), Forschungszentrum Karlsruhe, Postfach 3640, 76021 Karlsruhe, Germany.
3 Institute for Atmospheric and Climate Science, ETH Zurich, 8092, Zurich, Switzerland.
* To whom correspondence should be addressed.
J. P. D. Abbatt , E-mail: jabbatt{at}chem.utoronto.ca
Z. Kanji , E-mail: zkanji{at}chem.utoronto.ca
Laboratory measurements support a cirrus cloud formation pathway involving heterogeneous ice nucleation by solid ammonium sulfate aerosols. Ice formation occurs at low ice saturation ratios consistent with the formation of continental cirrus and an interhemispheric asymmetry observed for cloud onset. In a climate model, this mechanism provides a widespread source of ice nuclei, and leads to fewer but larger ice crystals as compared to a homogeneous freezing scenario. This reduces both the cloud albedo and the longwave heating by cirrus. With the global ammonia budget dominated by agricultural practices, this pathway might further couple anthropogenic activity to the climate system.
