Configuring Surface Charge (Coulombs) on particles in the Particle Tracing Physics?

I am working with Particle Tracing with Fluid flow physics. In the Particle properties menu, the options are fairly limited. I can configure the particle density, diameter and charge number (Z) only which is a mark of valency of species in flow. (See attached image)

How does one configure Surface charge (Coulombs) for the particles?

Thanks