In modern societies, people spend more than 80% of their time indoors, increasing their exposure to potentially hazardous indoor particulate matter (PM). Consequently, numerous studies have focused on reducing exposure to PM and its influence on the human body [1,2]. World Health Organization (WHO) guidelines recommend indoor concentrations of less than 10 and 20 μg/m for PM and PM, respectively, in line with atmospheric concentrations . In South Korea, the government has made efforts to reinforce indoor PM management by implementing the Indoor Air Quality Management Act and Enforcement Regulations (Ministry of Environment Decree No. 858, partial revisions on April 3rd, 2020). Furthermore, they have recommended that indoor concentrations of PM and PM should be maintained below 100 and 50 μg/m, respectively [4,5]. With growing concerns over the toxicity of PM and the health of indoor environments, various studies have been conducted regarding the reduction of indoor PM [, , ]. Respiratory and cardiovascular mortality has been attributed to PM, and the risk is higher for physically weak people, such as children and the elderly [9,10]. Furthermore, the International Agency for Research on Cancer (IARC) has classified PM as a group 1 carcinogen .
Dust can be classified into total suspended particles (TSP), PM (PM), and fine PM (FPM; PM) based on particle size criteria of 50, 10, and 2.5 ㎛, respectively . Outdoor PM is generated by both natural (e.g. fire, yellow dust, and volcanic eruptions) and artificial (power plants, industrial facilities, and automobiles) sources . Conversely, indoor PM tends to be generated by indoor activities such as cooking, which involves heating; smoking; occupant movement; and motion, and cleaning . Some indoor PM is deposited on surfaces and may impact the human body via resuspension due to changes in airflow caused by ventilation, ducts, and indoor activities [15,16].
Airflow (aerodynamic force) is a disturbance factor that affects the resuspension of indoor PM in addition to vibration (mechanical force) and static electricity (electrostatic force). Indoor PM is deposited by gravity and adhesion and is resuspended by airflow, vibration, and static electricity [17,18]. Resuspended PM may have a potential impact on occupants; for example, it can be inhaled by children when it suspended to their height . If PM deposited on the floor is not resuspended, it is less likely to impact the human body ; however, FPM in particular can be easily resuspended by indoor activities and ventilation . Therefore, it is necessary to reduce both deposited and suspended PM. To date, ventilation (natural and mechanical ventilation) and air purifiers have been mainly used to reduce indoor PM . Air purifiers reduce indoor pollutant concentrations by filtering gaseous and particulate pollutants that are present in the air [24,25]. However, current air purification technologies can only remove suspended PM and do not address deposited PM.
Grinshpun et al. . found that air purifiers could be used to reduce suspended PM in indoor spaces; however, residual PM can be deposited on indoor surfaces, impacting indoor air quality following resuspension. Golkarfard and Talebizadeh  used an airflow analysis simulation to investigate the deposition and suspension of indoor PM during the use of radiator and a floor heating systems; however, they did not consider the resuspension and reduction of PM. Chen et al . studied the deposition of indoor PM during the use of two types of cooling devices and confirmed that the deposition rate of indoor PM was high. Because their study focused on the behavior and deposition locations of indoor PM, the removal of deposited PM was not thoroughly investigated. These previous studies have investigated the deposition and resuspension characteristics of indoor PM to a certain extent; however, research with respect to the reduction of PM deposited on indoor surfaces is lacking.
Recent studies have considered the resuspension of particles by mechanical vibration and analyzed the degree of vibration, adhesion, and gravity applied to particles using simulations . Ahmed at al . studied the effects of floor materials on the resuspension of particulate matter. They found that resuspension was more dependent on floor hardness rather than roughness, and resuspension was the greatest from ceramic tiles compared PVC and linoleum flooring. Ahmed at al . conducted experiments to study the effect of walking inside a wooden chamber on resuspension. They found that PM10 was more actively resuspended compared to PM2.5 and PM1.0, and that wooden flooring caused more resuspension than linoleum flooring. Suihua at al . examined the effect of relative humidity on the resuspension of particulate matter by particle size. When the relative humidity was 60–70 % resuspension was higher compared to drier or more humid conditions. Furthermore, people walking had a greater impact on the resuspension of larger particles.
Numerous studies have investigated the likelihood and causes of PM resuspension. However, few studies have investigated the direct removal of deposited PM to reduce resuspension. Consequently, this study aims to investigate the impact of a forced resuspension method to effectively remove deposited PM. This study can be used as basic research for indoor air quality improvement by removing deposited PM that could adversely affect occupants. It can also be applied to air purification devices to improve the efficiency of indoor PM removal.