Abstract View
Numerical Investigation of Ion-condensation
Jacob Svensmark, MARTIN BØDKER ENGHOFF, Nir Joseph Shaviv, Henrik Svensmark, Technical University of Denmark
Abstract Number: 181
Working Group: Aerosol Physics
Abstract
The presence of small ions influences the growth dynamics of a size distribution of aerosols. Specifically, the often-neglected mass of small ions influences the growth velocity, which may be important for terrestrial cloud formation. To this end, we have developed a numerical model to calculate the growth of a population of aerosols in the presence of charges, which explicitly includes terms for ion-condensation (Svensmark et al 2019). It is shown that a positive contribution to aerosol growth velocity is obtained by increasing the ion-pair concentration, consistent with recent experimental findings (Svensmark et al, 2017).
The model is a zero-dimensional box model solving the general dynamics equation numerically using a 4th order Runge-Kutta algorithm. Six species are tracked individually: Neutral condensable gas, air ions of positive and negative charge, and stable aerosols of neutral, positive, and negative (single) charge. The aerosols are distributed in a number of logarithmically spaced nodes based on volume typically corresponding to aerosol diameters of 1-100 nm. Nucleation is not treated explicitly but input at a fixed rate which can be distributed between aerosols of all charges.
Unique to this model is that the addition of mass from the interactions between air ions and aerosols are taken into account.
Model runs for the sulphuric acid-water system are compared with an analytical expression for mass-dependent ion condensation, which is the classical condensation equation modified with a growth term relating to the ions.
The model can also be applied to other chemical systems if the interaction coefficients are recalculated.
The model can be downloaded at https://github.com/jacobsvensmark/ioncage
References
[1] Svensmark, J. and Shaviv N. J. and Enghoff M. B. and Svensmark H. (2019), arxiv.org/abs/1909.12784, in review for Earth and Space Science.
[2] Svensmark, H. and Enghoff, M. B. and Shaviv, N. J. and Svensmark, J. (2017), Nature Comm., 8:2199.