A 3D Time-Dependent Model for the Study of the Electrification of Non Spherical Dust Particles due to Ion Attachment
Authors: Mallios Sotirios , Daskalopoulou Vasiliki , Skoubris Evangelos , Hloupis George , Papaioannou Athanasios , Amiridis Vassilis 
Published: March 2020

&lt;p&gt;Electrical processes can be a potential key player in the lifecycle of desert dust. The dust particles can be charged during their transport, either by the attachment of atmospheric ions or by particle to particle collisions (triboelectric effect). Measurements indicate that, on average, larger particles become positively charged while the smaller ones become negatively charged [&lt;em&gt;Zhao, H. L.&lt;/em&gt;, J. Electrostat, 55, 2002; &lt;em&gt;Lacks, D.J.&lt;/em&gt;, et al., Phys. Rev. Lett., 100, 188305, 2008; &lt;em&gt;Merrison, J.P.&lt;/em&gt;, Aeolian Res., 4, 2012; &lt;em&gt;Shinbrot, T. and Herrmann, H.J.&lt;/em&gt;, Nature, 451, 2008]. During dust transportation, the larger and mainly positively charged particles separate from the smaller negatively charged particles due to the gravitational sedimentation, which sorts the dust particles by size. This process develops vertical electric fields within the dust cloud, enhancing the pre-existing field due to the depletion of atmospheric conductivity by the presence of the dust layer [&lt;em&gt;Gringel W. and Mulheisen. R.&lt;/em&gt;, Beitr. Phys. Atmos., 51, 121&amp;#8211;8, 1978]. Depending on its strength, the total electric field within the dust cloud can: (a) counteract the gravitational settling of large particles and (b) cause a preferential orientation of the non-spherical particles along the vertical direction affecting particle aerodynamics [&lt;em&gt;Ulanowski, Z., et al.&lt;/em&gt;, Atmos. Chem. Phys., 7, 2007]. Therefore, electrical processes may alter dust removal processes, and thus the evolution of particle size during transport, affecting dust-radiation-cloud interactions and the associated air quality [&lt;em&gt;Sajani S.Z., et al.&lt;/em&gt;, Occup. Environ. Med., 68(6), 2011], weather, and climate modeling [&lt;em&gt;Mahowald, N., et al.&lt;/em&gt;, Aeolian Res., 15, 2014].&lt;/p&gt;&lt;p&gt;In the present work, we have developed a novel 3D Cartesian time-dependent model that takes into account several atmospheric processes, such as: (i) the ionization due to the galactic cosmic rays radiation, (ii) the ion-ion recombination, and (iii) the ion attachment to non spherical dust particles. &amp;#160;The model is able to self-consistently calculate the time dynamics of the atmospheric conductivity, and the atmospheric electric field, under the presence of a distribution of stationary non spherical dust particles. Additionally, the total charge density, dust particle charge and dust particle orientation are also quantified. The new 3D electrification formalism allows the study of dust layers without imposing any symmetry and &amp;#160;is valid for layers with any horizontal and vertical extend, as opposed to 1D models which are valid when the horizontal extend is much larger than the vertical, or to 2D models which assume a symmetry in the shape of the dust layer. The results are compared, in the limiting case that the horizontal extend is much larger than the vertical one, with those obtained from 1D models found in the past literature [e.g. &lt;em&gt;Zhou, L., Tinsley, B.A.&lt;/em&gt;, Adv. Space Res. 50, 2012]. Moreover, the effect of the studied electrification process is assessed through a comparison with recent and unique electric field measurements within lofted dust layers, as performed with the use of novel low cost atmospheric electricity sensors in an experimental campaign of the D-TECT ERC project, in Cyprus the past November.&lt;/p&gt;