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Laboratory measurements of heterogeneous CO 2 ice nucleation on nanoparticles under conditions relevant to the Martian mesosphere
Author(s) -
Nachbar Mario,
Duft Denis,
Mangan Thomas Peter,
Martin Juan Carlos Gomez,
Plane John M. C.,
Leisner Thomas
Publication year - 2016
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
eISSN - 2169-9100
pISSN - 2169-9097
DOI - 10.1002/2015je004978
Subject(s) - nucleation , martian , ice nucleus , ice crystals , materials science , mesosphere , particle (ecology) , mars exploration program , atmosphere of mars , atmospheric temperature range , nanoparticle , supersaturation , ice cloud , chemical physics , atmospheric sciences , astrobiology , thermodynamics , physics , nanotechnology , geology , meteorology , radiative transfer , optics , stratosphere , oceanography
Clouds of CO 2 ice particles have been observed in the Martian mesosphere. These clouds are believed to be formed through heterogeneous nucleation of CO 2 on nanometer‐sized meteoric smoke particles (MSPs) or upward propagated Martian dust particles (MDPs). Large uncertainties still exist in parameterizing the microphysical formation process of these clouds as key physicochemical parameters are not well known. We present measurements on the nucleation and growth of CO 2 ice on sub‐4 nm radius iron oxide and silica particles representing MSPs at conditions close to the mesosphere of Mars. For both particle materials we determine the desorption energy of CO 2 to be Δ F des = (18.5 ± 0.2) kJ mol −1 corresponding to Δ F des = (0.192 ± 0.002) eV and obtain m = 0.78 ± 0.02 for the contact parameter that governs heterogeneous nucleation by analyzing the measurements using classical heterogeneous nucleation theory. We did not find any temperature dependence for the contact parameter in the temperature range examined (64 K to 73 K). By applying these values for MSPs in the Martian mesosphere, we derive characteristic temperatures for the onset of CO 2 ice nucleation, which are 8–18 K below the CO 2 frost point temperature, depending on particle size. This is in line with the occurrence of highly supersaturated conditions extending to 20 K below frost point temperature without the observation of clouds. Moreover, the sticking coefficient of CO 2 on solid CO 2 was determined to be near unity. We further argue that the same parameters can be applied to CO 2 nucleation on upward propagated MDPs.