Dynamics of the aerosol particle photocharging process

Abstract

In the photocharging process, aerosol particles become electrically charged through interaction with high-energy photons, e.g., ultraviolet (UV) irradiation. Photon adsorption by particles leads to electron emission and, as a result, particles become positively charged. While maximum achievable charges have been described in previous studies of dependency on particle and irradiation parameters, the influence of photoemitted charges on the charging process was not taken into account. In this work it is shown that such charges interact with the particles, which heavily influences the entire process. This complex process (the charging of particles positively by photons and simultaneously negatively by ions) is described in this work by a set of differential equations. These differential equations are solved numerically and, with simplifying assumptions, analytically. Multicomponent polydisperse aerosol is considered. As was found by comparing the analytical and numerical solutions, analytical results coincide with numerical ones for a wide range of initial parameters (particle number concentration, diameter). The analytical expressions evaluated allow one to quantify the influence of guiding processes and the limits of the charging process, which is heavily influenced by the previously neglected free ions. Model results explain such phenomena as the experimentally observed decrease in particle charge through the increase in particle number concentration. As a result of this work, the particle charge distribution obtained by the photocharging process can now be considered a known function of aerosol and UV-irradiation parameters.