Effects of triboelectric charging, flooring materials, relative humidity, and shoe sole materials on human walking-induced particle resuspension

Resuspension of settled particles via human activity is one of the primary sources of indoor aerosols. Previous studies have recognized the importance of electrostatic forces on particle resuspension, but the impact has not been well characterized. In this study, we measured the shoe sole electrostatic potential (static charge), airborne particle electrostatic charges, and airborne particle concentration during human stepping under different conditions to assess how these factors affect the resuspension rate of particle size ranging from 0.8 to 8 μm. Six flooring materials (aluminum with and without pattern, carpet, glass, polyvinyl chloride, Teflon, and tile) and three shoe sole materials (EVA, nylon, and rubber) under two relative humidity (RH) levels (normal RH: 60 ± 5% and high RH: 85 ± 5%) were tested. The measured surface static charges of different shoe sole materials before and after human stepping generally agreed with the material's tendency to gain or lose electrons in the triboelectric series. The results also showed that the resuspension rate consistently increased with the increase of particle sizes for all tested scenarios, while it decreased with the increase in RH. Besides, the carpet always gave the highest value for the resuspension rate, while the tile gave the lowest. The data indicated a positive correlation between the charge of resuspended particles and the resuspension rate. In addition, EVA shoe soles generally resulted in higher resuspension rates than shoe soles made of nylon and rubber. This study elucidates the role of electrostatic charge on walking-induced particle resuspension for common materials and helps to assess human exposure to particulate matter.