The importance of determining the instantaneous resuspension rate of deposited inhalable particles under human walking indoors: A review

Aerosol particles with aerodynamic diameter less than 10 μn can deposit anywhere in the human respiratory system and are termed inhalable particles PM10 by EPA, USA. The presence of inhalable particles PM10 indoors can significantly deteriorate indoor air quality and is closely related to many health issues as well as the transmission of infectious diseases. Recent researches have identified that the resuspension of deposited PM10 from indoor surfaces by human walking indoors is one of the major sources of inhalable particles, which could seriously increase the human exposure risks to particles. To fully quantitatively understand the human exposure risks to the resuspended PM10 the most significant quantity is the instantaneous resuspension rate, which is vital to the mathematical model development of computational fluid dynamics (CFD) simulation involving human-walking-induced particles resuspension. In this study the literatures related to the experimental measurements, theoretical and numerical investigations on human-walking-induced particles resuspension were systematically reviewed, with the emphasis on the methodologies of determining the instantaneous resuspension rate of PM10 in indoor air environment. It is found that, the previously developed theoretical models of resuspension rate based on the forces or energy balances can generally benefit the overall understanding of particles resuspension mechanisms, but still with several unsatisfactory aspects like the relatively large differences between the theoretical calculations and the measurements, the inconvenience to be incorporated into the CFD code due to large computation time to resolve the theoretical resuspension rate. On the other hand, the other macro empirical models based on wind tunnel experiments can be conveniently incorporated into CFD code, but with the deficiencies of not considering human walking impacts. As to the previous measurement methods there are generally three major deficiencies, that is, (1) without considering human walking impacts or not real human walking, (2) the time-averaged resuspension rate over a relatively long period instead of the instantaneous one, (3) the derived resuspension rate from particles mass balance based on the well-mixing indoor airflow assumptions. Finally, the measurement methods for instantaneous resuspension rate of PM10 under human walking and the CFD simulation methods based on the instantaneous one are suggested.