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Publication Date

Summer 2011

Degree Type

Thesis - Campus Access Only

Degree Name

Master of Science (MS)




Bradley M. Stone


Clouds, Ice, Mars, Nucleation, Water

Subject Areas

Physical chemistry; Atmospheric chemistry


Water vapor in the martian atmosphere, while significantly less abundant than on Earth, is still present in sufficient quantities to form clouds, and these clouds play a crucial role in the martian climate. It is therefore critical that any attempt to model the martian atmosphere include a robust handling of the formation and growth of these clouds. Presented here are the results of laboratory studies at simulated martian temperature and water vapor partial pressure (150-185 K and 1.0 · 10-6 - 1.0 · 10-4 Torr) designed to probe the behavior of two parameters critical for modeling the life cycle of a martian cloud. The first of these parameters is the critical saturation ratio (Scrit), which is a measure of the threshold of water vapor pressure required in the system to facilitate formation of cloud particles of the necessary size to initiate cloud growth. Scrit was measured as a function of temperature and nucleation substrate, with silica and sulfate-functionalized polystyrene microspheres being the substrates tested. Of these two substrates, the latter was found to be the stronger nucleator, with nucleation efficiency higher than any previously tested substrates except smectite clay. The second parameter was the condensation coefficient, α, which is the ratio of the measured ice growth rate to the maximum growth rate at the corresponding experimental pressure, given by the collision frequency. For the above range of conditions, alpha; can be represented as a function of temperature offset from the solid-vapor phase boundary as α(ΔT) = 1 − e0.1884ΔT.