Numerical modeling of multi-component aerosol evolution under energetic dispersal conditions

The release of radioactive substances through explosive dispersal presents a critical challenge for radiological emergency preparedness, owing to the rapid generation of complex multi-component aerosols under highly transient thermodynamic conditions. In this study, a numerical framework is developed that explicitly resolves nucleation, condensation, coagulation, and dilution to simulate the evolution of multi-component aerosols containing both radioactive and non-radioactive constituents. For a representative case (20 kg TNT dispersal of 10,000 Ci of Co-60), the model predicts the formation of ∼0.4 nm Co-60 clusters within 1 ms, which subsequently condense onto carbonaceous detonation products, producing mixed-component particles that dominate the accumulation mode. The resulting activity median aerodynamic diameter (AMAD) stabilizes at ∼270 nm with a geometric standard deviation of ∼1.26, consistent with field measurements (200–500 nm). Parametric analyses reveal that particle size distributions are largely insensitive to source activity levels, with higher inventories increasing activity per particle but not AMAD. Increasing explosive mass produces larger clouds and greater numbers of contaminated particles but reduces activity per particle through enhanced dilution. Simulations of surface detonations show that dust entrainment contributes negligibly to respirable activity fractions, with radionuclides preferentially partitioning onto submicron soot particles. These results demonstrate that realistic source-term characterization must include multi-component aerosol dynamics, as simplifications assuming monodisperse radioactive particles can overestimate ultrafine fractions and underestimate accumulation-mode dominance. The model thus provides a framework for improving radiological consequence assessments and guiding emergency response planning.