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. Möhler2
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 with 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.
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. E-mail: jabbatt{at}chem.utoronto.ca
