Exposure to airborne particles has a negative effect on
the respiratory health of occupants (Schneider et al.,
2003). Influence of airborne particles on health effects
is strongly related to particle size, and the particle size
is also closely related to filtration and penetration in
buildings. When there are no indoor particle sources,
filtration, deposition, and penetration become important
factors to determine indoor airborne particle concentrations
(Liu and Nazaroff, 2001). Mechanical
ventilation systems are commonly equipped with filters
to remove particles from outdoor air and recirculated
indoor air. Previous studies showed that buildings with
mechanical fans and air filtration have lower indoor
levels of airborne particles, compared with outdoor air,
in the absence of indoor sources (Stephens and Siegel,
2012; Zhang and Zhu, 2012).