Parameterization for two-component H2SO4 - H2O nucleation applicable for very low relative humidities and correct at the one-component limit

Abstract : We have extended the Vehkamäki et al. (2002) twocomponent nucleation parameterization for sulfuric acid and water in stratospheric conditions to very low relative humidities where nucleation of pure sulfuric acid becomes possible. Our motivation for this work was an application to the extremely dry atmosphere of Venus, where relative humidities can fall below the lowest limit of the Vehkamäki et al. (2002) parameterization, RH=0,01%. According to observations, sulfuric acid aerosols are the main component forming the clouds on Venus. The clouds are optically thick in the visible wavelengths masking the surface of the planet from visual observation. The clouds are organized in three quite distinct layers with differing droplet size distributions and probably differing composition. Hints from early observations on possible existence of other species than sulfuric acid in the clouds have not yet been confirmed by recent missions. It is thought that the water - sulfuric acid droplets form by binary homogeneous nucleation in both the Earth's stratosphere and the atmosphere of Venus. In this study we focus on homogeneous nucleation only. However, the existence of condensation nuclei on Venus cannot be ruled out in lack of observational evidence. We have used the thermodynamically consistent version of the Classical Nucleation Theory (Noppel et al., 2002). The 2002 model was improved by deriving analytical formulae for the second derivatives of the formation free energy, since the numerical derivatives were unstable at the limit of one-component system.
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Contributor : Catherine Cardon <>
Submitted on : Wednesday, November 7, 2012 - 1:12:49 PM
Last modification on : Tuesday, May 14, 2019 - 11:09:55 AM

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  • HAL Id : hal-00749363, version 1

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Anni Määttänen, J. Julin, I. K. Ortega, H. Vehkamäki. Parameterization for two-component H2SO4 - H2O nucleation applicable for very low relative humidities and correct at the one-component limit. EAC 2012, European Aerosol Conference, Sep 2012, Granada, Spain. ⟨hal-00749363⟩

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