Public defense of the PhD thesis titled "The Role of Clothing in Influencing Inhalation Exposure to Airborne Particles."

This research was conducted at the Human-Oriented Built Environment Lab (HOBEL) under the supervision of Prof. Dusan Licina.

Abstract

People spend significant time in close contact with clothing, which can harbor chemicals, particles, and microbes. During everyday activities such as walking or crawling, some particles can detach from the fabric and become airborne, eventually settling in respiratory tracts. This phenomenon, known as particle resuspension, is a significant source of abiotic and biotic indoor airborne particles. Resuspension from clothing is recognized as a critical pathway for indoor exposure, enhanced by the 'personal cloud effect'—a phenomenon where particle concentrations around an individual are higher than average room levels. Recent studies have also indicated that clothing could play a critical role in the transmission of viruses. For instance, the SARS-CoV-2 virus can remain active on fabrics for hours or even days.

Despite the importance of clothing for inhalation exposures, previous resuspension studies mainly focused on other indoor surfaces, such as flooring. Experimental data on particle deposition onto and resuspension from clothing are still limited, and the influencing factors are unclear. According to the findings of previous research on particle resuspension from flooring, factors affecting particle resuspension associated with clothing from human activities could include intrinsic factors, such as fabric properties; environmental factors, such as relative humidity and air movement; and human factors, such as movement intensity.

This thesis utilized a breathing and moving thermal manikin in controlled environmental chambers to investigate particle resuspension from clothing, with particle sizes ranging from 0.3 μm to 10 μm. It provided experimental data quantifying size-resolved particle deposition and resuspension rates associated with clothing. The research encompasses three objectives: (1) to compare the PM2.5 and PM10 concentrations in the breathing zones of the manikin and a human subject during resuspension activities, (2) to investigate particle deposition on the thermal manikin in a sitting posture while wearing different types of clothing materials, and (3) to quantify the resuspension of particles from clothing to various clothing, environmental, and human factors.

The results show that the surface roughness of the manikin employed in this thesis closely approximates that of human skin. This similarity justifies using thermal manikin in simulating the friction between clothing and human skin in resuspension experiments. Additionally, it has been demonstrated that, during identical resuspension activities, the levels of PM2.5 and PM10 for humans and the breathing thermal manikin wearing the same contaminated clothing were comparable. Particle deposition rates on clothing increased exponentially with particle size and were proportional to indoor air speed. Clothing material strongly influenced particle deposition loss rate coefficients. The highest deposition loss rate coefficients were associated with wool/polyamide, followed by fleece, polyester, and cotton, while bare skin exhibited the lowest deposition rates. Additionally, positive correlations were observed between deposition rates and the surface roughness of the clothing.

In resuspension experiments, the short-term PM10 concentration in the breathing zone of the manikin was 1.25 times higher than in the bulk air when the seated manikin performed arm movements at frequencies of 0.25, 0.5 and 0.75 Hz using a consistent test mechanism. The size-dependent resuspension rates varied between 0.01 h⁻¹ and 0.06 h⁻¹. Higher resuspension rates were associated with increased movement intensity and dust loading on clothing, while no significant dependence was found on clothing type and relative humidity. The findings in this thesis offer a valuable dataset for enhancing current inhalation exposure models related to indoor aerosols and for developing interventions to reduce exposure to particles associated with clothing.