An experimental and simulation study of the effect of charged aerosol ingress and deposition in dwellings

Radioactive aerosol of accidental origin can travel long distances once airborne and although dwellings can provide some shelter, ingressed radioactive aerosol has been shown to be injurious to human health. The deposition of radioactive aerosol, which are potentially harmful to human health, is influenced by their ability to self-charge via ionization. This relationship which has rarely been studied was investigated by corona-charging particles in three sizes (0.5 µm, 1.0 µm and 2.0 µm) in a test chamber to levels representative of radioactive aerosol. The aerosol deposition velocities were calculated for each size fraction under a variety of conditions, which consisted of using two chamber airflow rates, three charging regimes (producing a strong positive charge, a strong negative charge, and no corona charge), and three interior wall surfaces (aluminium, wallpaper, and polyethylene). No significant difference in deposition velocity was detected between the charged aerosol, regardless of their polarity, but the deposition velocity of the charged aerosol exceeded that of the uncharged aerosol by as much as 72%. All of the size fractions, irrespective of the charging regime, exhibited the highest deposition rates when the chamber walls were lined with polyethylene, with values that were 4 – 8 times higher than those calculated for aluminium lining. Modelling approaches have been widely used to study indoor aerosol behaviour, but such approaches have not to date considered the self-charging nature of radioactive aerosol and the consequent effect upon aerosol deposition. In this work, a multi-zone modelling tool is used to simulate indoor aerosol concentrations in the individual rooms of a bungalow and semi-detached dwelling, for three radioactive aerosol particles sizes (0.5, 1.0, 2.0 μm, with aerosol deposition enhancement due to particle charge), two plume types (5 h and 24 h), and a range of representative dwelling airflow conditions (low air flow LAF and high air flow HAF1), including mechanical extract ventilation (HAF2). When comparing the time series of aerosol concentrations in different rooms, lower concentrations of charged aerosol, relative to uncharged, were observed, suggesting charge-enhanced deposition, and this phenomena is more striking during a 24 h plume compared to 5 h plume, where the difference between the two is up to 50% in one of the zones of the dwelling. The concentration comparison of charged aerosol concentration between LAF and HAF1 cases also showed that during a 5 h plume, the aerosol concentration is twice as high for the HAF1 case. These simulation results demonstrate that the effect of charged-enhanced aerosol deposition should be considered when assessing the benefits of sheltering in a building in the event of a nuclear accident.

Funder

University of Galway

Publisher

University of Galway

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CC BY-NC-ND

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University of Galway Theses (Research Masters Theses)