Aerosol Particle Effects on Warm and Cold Cloud Formation

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All cloud droplets and many ice crystals form on suspended particles in the atmosphere. This laboratory investigation will study key aspects of these "nucleation" processes. The study emphasizes the nucleating properties of organic material (including pure organic species and the organic material in soils) and mineral dust because they have not been studied extensively before and there is an increasing body of evidence that points to their importance in the atmosphere. Three different kinds of laboratory measurement will be made: water uptake on particles in subsaturated conditions, activity of particles as cloud-condensation nuclei (CCN), and ice nucleation of pure solution droplets or caused by undissolved particles. Samples of soil from regions that are significant sources of desert dust will be collected and re-suspended for these analyses. A key hypothesis to be tested is that the characteristics of dust from different arid regions of the world have similar characteristics and so might be represented by common parameterizations. Other objectives of this project will be to examine particles of known mixed composition and to develop and test parametric representations of the results. The expected result is new characterization of the nucleating properties of some key constituents of the atmospheric aerosol and the development of new ways of representing those characteristics that can be used in weather and climate models of those processes. This has potential to influence future forecasts of precipitation and representations of the important radiative properties of clouds in climate models.