Modeling Water Uptake of Dust in the Indoor Environment
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Date
2019-05
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The Ohio State University
Abstract
Moisture found within homes can impact microbial growth in dust and contribute to negative human health effects. There are mathematical models of the adsorption of moisture on outdoor particles, but there is currently no mathematical model for moisture uptake and microbial growth in dust within homes. The goal of this research was to use an atmospheric mathematical model to inform a model for indoor dust to predict moisture uptake. Thermodynamic and kinetic models were utilized with Arizona Test Dust, a well characterized model dust. To compare to the thermodynamic models, the dust was incubated at equilibrium relative humidity conditions from 50-100% in intervals of 10% for 1-day increments. Two thermodynamic models were evaluated, one using values obtained from literature (Model A), and the other using values based on our experimental data (Model B). To compare to the kinetic model, we increased the relative humidity from 50% to 100%, and tested at time points up to 6 hours. Two kinetic models were used, one modeled as spherical particles and the other based on a planar sample. Water activity and water content were used to infer water intake. Mass ratios and differences were measured to compare to the previous atmospheric models. The thermodynamic experiments resulted in an exponential curve, similar to the model, however the mass ratio in the model was approximately 70% higher than the results at 100% ERH, 20% higher at 90% ERH, and 5% higher at 80% ERH for Model A. This demonstrates that the dust is absorbing less water than predicted by the model. For Model B, all the samples were within 5% error at all ERH values, except for 100% ERH. The kinetic experiments resulted in the model and the observed data closely matching at 82% ERH when accounting for a planar model, but at 100% and 95% ERH, the equilibrium mass difference was double the model prediction. This could be due to condensation in the cup. A hysteresis effect was observed, showing that the dust retained water after reaching the 100% ERH value. The growth of microbial species caused a decreased hysteresis effect. Future work will consist of further testing of the models with both the model dust and house dust with the ultimate goal of improved modeling of water uptake in indoor dust.