Aerodynamic resuspension and contact removal of energetic particles from smooth, rough, and fibrous surfaces

Surface sampling for trace explosives residues is a critical step in the security screening in which microparticles are collected for subsequent chemical analysis. The current surface swabbing approach suffers from limited sampling area coverage, uncertainty in harvesting efficiencies, and user bias. Non-contact sampling has received interest due to its ability to interrogate large surface areas without the redeposition of the collected sample. However, the aerodynamic liberation of energetic particles from different types of substrates has not been parameterized or directly compared with the contact sampling methods. Here, we report aerodynamic resuspension rates of TNT, RDX, and HMX microparticles from smooth, rough, and fibrous surfaces. The resuspension thresholds are correlated to the boundary layer properties, i.e., wall shear stresses (τ_w = 50-500Pa). These rates are then compared to contact sampling for five commercial swabs using a standardized swabbing method. LC-MS analysis is used for the quantification of particle removal efficiencies. Contact sampling has an advantage over the low shear stress cases for particle liberation from the smooth surfaces. Aerodynamic particle resuspension rates increase with the wall shear stress. It shows better results for rough and fibrous surfaces than contact removal for tested analytes.