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Issue 5, 2017
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The frequency-dependent response of single aerosol particles to vapour phase oscillations and its application in measuring diffusion coefficients

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Abstract

A new method for measuring diffusion in the condensed phase of single aerosol particles is proposed and demonstrated. The technique is based on the frequency-dependent response of a binary particle to oscillations in the vapour phase of one of its chemical components. We discuss how this physical situation allows for what would typically be a non-linear boundary value problem to be approximately reduced to a linear boundary value problem. For the case of aqueous aerosol particles, we investigate the accuracy of the closed-form analytical solution to this linear problem through a comparison with the numerical solution of the full problem. Then, using experimentally measured whispering gallery modes to track the frequency-dependent response of aqueous particles to relative humidity oscillations, we determine diffusion coefficients as a function of water activity. The measured diffusion coefficients are compared to previously reported values found using the two common experiments: (i) the analysis of the sorption/desorption of water from a particle after a step-wise change to the surrounding relative humidity and (ii) the isotopic exchange of water between a particle and the vapour phase. The technique presented here has two main strengths: first, when compared to the sorption/desorption experiment, it does not require the numerical evaluation of a boundary value problem during the fitting process as a closed-form expression is available. Second, when compared to the isotope exchange experiment, it does not require the use of labeled molecules. Therefore, the frequency-dependent experiment retains the advantages of these two commonly used methods but does not suffer from their drawbacks.

Graphical abstract: The frequency-dependent response of single aerosol particles to vapour phase oscillations and its application in measuring diffusion coefficients

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Publication details

The article was received on 10 Nov 2016, accepted on 10 Jan 2017 and first published on 13 Jan 2017


Article type: Paper
DOI: 10.1039/C6CP07711K
Citation: Phys. Chem. Chem. Phys., 2017,19, 3922-3931
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    The frequency-dependent response of single aerosol particles to vapour phase oscillations and its application in measuring diffusion coefficients

    T. C. Preston, J. F. Davies and K. R. Wilson, Phys. Chem. Chem. Phys., 2017, 19, 3922
    DOI: 10.1039/C6CP07711K

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