Application of Resuspension Data of Respirable Particles for Early Phase Inhalation Following Deposition Contamination in Radiological Emergencies

In model experiments, wind resuspension rates, Rr, of respirable particles (<10 mm, aerodynamic diameter) and their time dependence after deposition on representatively contaminated urban surfaces were measured under real-life conditions, taking into account different weather conditions (wind velocities, precipitation) as well as countermeasures (fixation). For contamination by dry deposition of particles, short-term resuspension rates averaged over the first halfhour, Rr, after exposure towind with a friction velocity, u*, of0.8 m s−1 ranged between 0.1% h−1 and 2%h−1 depending on the surface material,whereas afterwet deposition, resuspension rates were two orders ofmagnitude lower. The time pattern of the resuspension rates followed a power law decrease, Rr ∝ t m,withvalues of m close to 1. The measurements revealed a strong dependence on friction velocity, Rr∝u 2:5. For a larger area of200 800m2 contaminated with 106 Bq m−2 of particles in the respirable size range, applying a simple Gaussian dispersion model airborne activity concentration (Bq m−3) was calculated. On this basis, for an initial time ofhigh windspeed, a cautious resuspension factor ofRf =5 10−6 m−1 is derived for the first day, which diminishes inversely with time. The exposure ofpersons to external radiation and to inhaled airborne radioactivity is compared with examples for three radionuclides representing strong beta-, gamma- and alpha-radiation.