Suspension and resuspension of dry soil indoors following track-in on footwear |
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Authors: | Andrew Hunt David L Johnson |
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Institution: | (1) Department of Earth and Environmental Sciences, University of Texas at Arlington, 500 Yates Street, Box 19049, Arlington, TX 76019-0049, USA;(2) Department of Chemistry, State University of New York College of Environmental Science and Forestry, Syracuse, NY, USA |
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Abstract: | Contamination of the indoor environment by tracked-in outdoor soil has the potential to pose a significant human health threat
through exposure to hazardous soil constituents. The indoor distribution of (contaminated) soil following ingress is important
when evaluating exposure risk. Here, the time evolution of size-resolved airborne particulate matter aerosolized as a result
of mechanical (i.e., footfall or step-on) impacts on a floor surface with a layer of dry soil was investigated using laser
particle counters. Suspended particle levels were recorded after step-on impacts that aerosolized soil particles at a single
contact point by the action of a human tester who followed a pre-determined walking pattern. The experimental design presumed
that the floor area immediately upon entrance indoors is the location of maximum deposition of outdoor soil transferred on
footwear. The suspension of soil resulting from the first step-on floor contact and the subsequent resuspension of soil resulting
from additional step-on events were quantified by various arrangements of four laser particle counters. Step-on impacts produced
a transient increase in particle levels at various lateral distances and heights from the contact point. Also, with increasing
distance and height from the step-on contact point, the level of suspended particles after successive step-on events decreased
markedly. The results suggested that a lateral component of the dispersion process was more significant than a vertical one
under these experimental conditions. A wall jet effect created by the impact of the footfalls on the floor surface was considered
responsible for the apparent greater lateral dispersion of the soil particles. |
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