Ice nucleation on soot particles

The ice-forming activity of soot particles of various sizes has been studied in a cloud chamber under temperatures ranging from -5 to -20 degreesC, It was found that the fraction of aerosol particles forming ice crystals was influenced by the temperature, the mean radius of aerosol particles and the degree of oxidising of the soot particle surface. It was suggested that oxidising affected the concentration of surface chemical groups that could form hydrogen bonds with water molecules. A decrease in the temperature and an increase in the radius of particles led to an increase in the number of ice crystals. Data obtained were parameterised and an expression was derived that enables the concentration of ice crystals to be calculated for conditions in a low cloud. Based on these experiments, this particular soot is a very potent source of ice nuclei. Data obtained were compared with Fletcher theory. It was shown that the theory contradicts experimental data and cannot be recommended for evaluation of the number of ice crystals in clouds. An application of the data obtained to aircraft condensation trail formation is discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.