Abstract
The attachment of positive and negative ions to settling spherical dust particles is studied. A novel 1D numerical model has been developed to parameterize the charging process in the presence of a large-scale electric field. The model is able to self-consistently calculate the modification of atmospheric ion densities in the presence of the dust particles, and the consequent alteration of the atmospheric electrical conductivity and the large-scale electric field. Moreover, the model estimates the acquired electrical charge on the dust particles and calculates the electrical force that is applied on them. Using observed dust size distributions, we find that the particles can acquire electrical charge in the range of 1–1,000 elementary charges depending on their size and number density. The particles become mainly negatively charged, but under specific conditions giant mode particles (larger than 50 μm radius) can be positive. Moreover, the large-scale electric field can increase up to 20 times as much as the fair weather value. However, our approach shows that the resultant electrical force is not enough to significantly influence their gravitational settling, as the ratio between the electrical force magnitude and the gravity magnitude does not exceed the value of 0.01. This indicates that the process of ion attachment alone is not sufficient to create strong electrical effects for the modification of particle dynamics. Therefore, other processes, such as the triboelectric effect and updrafts, must be included in the model to fully represent the impact of electricity on particle dynamics.
Highlights
Mineral dust plays an important role in the Earth’s atmosphere, and in the Earth System in total
Motivated by the studies of dust particle electrification and charging, we focus on dust charging due to ion attachment process and we develop an 1D numerical model for the of spherical dust particle settling in the presence of a large scale electric field
In the region below the main dust layer, where the ion density increases to the fair weather values, the falling dust particles encounter a larger pool of ions available for attachment than the one within the layer
Summary
Mineral dust plays an important role in the Earth’s atmosphere, and in the Earth System in total. It significantly impacts radiation (Li et al, 2004), as dust particles absorb shortwave and long-wave radiations, potentially causing a net atmospheric warming (Kok et al, 2017). The lifetime of the mineral dust particles affects the deposition fluxes over land and ocean (van der Does et al, 2018). Once dust particles are deposited at the surface, they provide micro nutrients to the ocean or to land ecosystems (e.g., Jickells et al, 2005). All aforementioned processes are strongly affected by the dust Particle Size Distribution (PSD). Earth System Models and transport models fail to properly
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