Indoor Aerosol Sensing and Resuspension Dynamic

Exposure to indoor particulate matter (PM) is associated with adverse health effects. Controlling the indoor PM exposure relies on an accurate understanding of aerosol transport, as well as accurate real-time monitoring of PM concentration level in the indoor environment.;Indoor aerosol transport is a cycle involving continuous repetitions of deposition and resuspension of particles from indoor surfaces. Occupants' activities such as walking, and indoor environmental conditions such as relative humidity (RH), influence the resuspension rate of particles. The first objective of this dissertation was to investigate the effects of RH and turbulent air swirls on the resuspension rate of allergen carrier particles from indoor surfaces.;This study shows that increasing RH can reduce the resuspension and spread of hydrophilic particles such as dust mites and that the presence of carpet significantly increased resuspension rates compared to linoleum flooring surfaces. This study also analyzes the efficacy of indoor PM sensing with current technologies. Effective PM removal strategies depend on continuous monitoring of indoor aerosols. Although PM monitoring in buildings has not been feasible due to high PM sensor cost, the recent advent of low-cost optical PM sensors has enabled real-time PM monitoring with high spatiotemporal resolution. Since biological particles such as dust mites, pollen, and pet dander are linked to respiratory and allergic symptoms among building occupants, PM sensors can be utilized to accurately measure bioaerosols. However, the performance of low-cost particle sensors in monitoring bioaerosols is under-investigated. Thus, the second objective of this dissertation was to evaluate the performance of low-cost optical particle counters (OPC) in monitoring the common indoor bioaerosols. Controlled chamber experiment results showed that low-cost OPCs performance is strongly influenced by particle concentrations being measured. Low-cost OPCs did not show a linear response compared to the reference sensor in the concentration range less than 5/cm3 for measuring PM 2.5 bioaerosol concentrations, while the tested sensors exhibited more linear responses in the range greater than 5/cm3. For each low-cost OPC, particle-specific, as well as average linear calibration equations that work well for the aggregate of tested bioaerosols, were developed.;One of the challenges in particle monitoring is size characterization due to the variable and irregular shapes. Usually, for application purposes, particles are assumed to be perfect spheres with corresponding spherical physical behaviors and properties. The general process typically defines a sphere with similar physical properties and assigns it an equivalent diameter size. Aerodynamic equivalent diameter is the most commonly used particle size. While aerodynamic size characterization is required for PM transport and exposure studies, optical-based sensors are used in place of aerodynamic-based sensing in most field applications. The validity of such practice has been called into question by previous studies and further investigation of the relationship between aerodynamic and optical size measurement is necessary. Consequently, the third objective of this dissertation was to experimentally compare the size-resolved concentration measurements of an aerodynamic particle sizer with an optical particle counter. Comparison of multiple tests with sixteen -monodisperse and polydisperse, biological and non-biological- particles showed that the particle type, size, and the measurement size fraction affect the relationship between the two PM sensing techniques. Accordingly, particle type and size-resolved specific empirical linear calibration curves between the two sensors for size fractions of smaller than 10 mum, smaller than 2.5 mum, and total number counts were provided. These calibrations provide an opportunity for real-world application of current technologies to reduce the PM exposure health risks for the public.