A laboratory study of the effects of a kerosene-burner exhaust on ice nucleation and the evaporation rate of ice crystals

Laboratory experiments are described during which the influence of gases and particles from the exhaust of a kerosene burner on microphysical processes were studied. In one experimental investigation the evaporation rates of ice crystals polluted with the kerosene-burner exhaust were compared with the evaporation rates of pure ice crystals. During another experimental investigation the ice nucleating ability of the exhaust particles was studied in terms of the efficiency of the exhaust particles to act as deposition and condensation freezing nuclei, as immersion freezing nuclei, and as contact nuclei. The results of our experiments showed that the evaporation rate of ice crystals polluted with the kerosene-burner exhaust was significantly reduced compared to the evaporation rate of pure ice crystals, implying an increased lifetime of aircraft contrails in comparison to a cloud of pure ice crystals. We also found that the kerosene-burner exhaust particles act as ice nuclei in all studied modes of ice formation at temperatures as high as -20 degrees C, particulary freezing between 20 and 70% of the drops at temperatures warmer than -28 degrees C in the immersion mode. Since the temperature at the level of the contrails is typically below -30 degrees C our result allows the speculation that drop formation at the cruising altitude of air planes is immediately followed by ice crystal formation via heterogeneous nucleation. (C) 1998 Elsevier Science Ltd. All rights reserved.