(263g) Influence of Radioactivity-Induced Charging on Aerosol Interactions

Electrostatic aerosol interactions are typically assumed negligible in modeling studies of size and composition evolution of radioactive aerosols. Radioactive decay of radionuclides, however, can produces charge on the surface of aerosols in the atmosphere, suggesting that strong electrostatic forces can be generated among aerosols. Electrostatic interactions can impact the aerosol coagulation rate; thus, this research is aimed at assessing the influence of radioactivity-induced charging (RiC) on the coagulation of radioactive and background aerosols. A sectional approach is used to simulate the charging and coagulation of size-resolved radioactive and background aerosols, where RiC effects on the coagulation of aerosols are considered. Simulation results obtained without considering electrostatic aerosol interactions are used for reference. It was found that highly radioactive aerosols can be positively charged in the atmosphere while urban aerosols can be negatively charged. The different charging states of the aerosols that were attributed to RiC can be classified as self-charging and diffusion charging. Many radioactive aerosols acquire an excessive number of positive charges after the competition of self-charging and diffusion charging, while large urban aerosols acquire negative charge due to diffusion charging driven by negative ions. Due to strong electrostatic attractive forces produced between positively and negatively charged aerosols, radioactive aerosols coagulate frequently with many micron-size urban aerosols. Because micron-size urban aerosols become radioactive due to coagulation, the size distributions of radioactive and background aerosols become significantly different from those of the reference simulation, suggesting that electrostatic aerosol interactions should be taken into account in investigations of size and composition evolution of radioactive aerosols. Results on the impact of the microphysical behavior on radioactivity transport in the atmosphere are discussed.