A study of the size distribution of aerosol particles resuspended from clothing surfaces

A primary factor governing the impact of hazardous aerosol particles on the human body is the size of the contaminant particles. Secondary exposure to humans can occur when initially deposited particles are re-entrained into the air via the transport process of resuspension. This study has experimentally investigated the size distributions of a mixture of monodisperse 3, 5, and 10 mu m particles after they were collectively deposited on, and then resuspended from the clothing of a contaminated person engaged in varying degrees of physical activity. The generally accepted theory, that the likelihood of particles resuspending from a surface will increase with increasing particle size, has been verified in this study (i) by comparing the size distribution curves of airborne particles during deposition and during resuspension, (ii) by examination of the individual size distributions for each of the three particle sizes investigated, and (iii) by calculating the resuspended fraction of initially deposited particles, as determined via Neutron Activation Analysis (NAA). A comparison of the size distribution curves for deposited and resuspended particles revealed that during resuspension, the highest peak in concentration occurred at similar to 10 mu m, whereas the highest concentration peak occurred at similar to 3 mu m during deposition. When the three distributions were individually analysed, it revealed a shift towards a higher Mass Median Aerodynamic Diameter for the resuspended distribution. This was confirmed via NAA, which revealed that the percentage of particles resuspended increased with increasing particle size; during high physical activity, an average of 27 +/- 9% of 3 mu m particles, 30 +/- 6% of 5 mu m particles, and 34 +/- 5% of 10 mu m particles resuspended. Additionally, it was revealed that following the collective resuspension of 3, 5 and 10 mu m sized particles, the larger sized particles were found at their highest concentrations at head height (in comparison to ankle or waist height). This has consequences for a person's potential inhalation exposure; larger particles are less likely to penetrate the lower airways of the lungs, and therefore resuspended aerosol particles do not pose a major threat for increased inhalation exposure. (C) 2014 Elsevier Ltd. All rights reserved.