Brownian dynamics determination of the bipolar steady state charge distribution on spheres and non-spheres in the transition regime

A Brownian Dynamics (BD) method to calculate the steady state charge distribution on spherical and non-spherical aerosol particles is presented which circumvents ion-particle collision rate calculation. BD calculations are performed using both monodisperse and measured polydisperse ion properties under atmospheric pressure, room temperature conditions. Calculations reveal that for spherical particles in both the nano- and submicrometer size ranges, the fractions of charged particles are noticeably underpredicted by flux matching theory-based regression expressions. In the examination of non-spherical particles (aggregates, linear chains and cylinders), two models for accumulated particle charge are employed: (1) accumulated charge distributes itself along a particle surface, and (2) accumulated charge is immobile. Independent of model, it is found that particles having a Projected Area (PA) to diffusion based surface area (πRs2) ratio close to unity behaves similar to a sphere of the same mobility diameter. However, model specific behavior is observed for highly non-spherical particles (PA/πRs2