Penetration coefficient and deposition rate as a function of particle size in non-smoking naturally ventilated residences

In residential environments without the operation of mechanical ventilation, infiltration becomes the dominant ventilation mode and deposition on material surface is one of the major particle losses, while penetration determines how much ambient particle can be brought from outside into the indoor environment. This study presents results based on measurements conducted in six non-smoking residences in high-rise apartment buildings. The effect of particle size from 0.02 to 10 μm was evaluated. A simplified indoor particle model was constructed to facilitate the calculation. The deposition rate and the penetration coefficient were determined according to a decay rate constant and the steady-state particle concentration in the transient form of the indoor particle concentration decay profile. Both of them were particle-size dependent but showed a different up-and-down inversion profile against the particle size. The major causes of the depositional losses and the penetration effects are diffusion, inertial impaction/interception and settling. They reduce the penetration and enhance the deposition in the size ranges of ultra-fine and coarse mode particles. The penetration coefficient showed a hill-shape with respect to particle sizes and there was a peak (0.79) at the size range of 0.853–1.382 μm. It decreased on both smaller and larger particle size ranges and the minimum particle penetration coefficient was 0.48 at the particle size range 4.698–9.647 μm. Deposition rate showed a converse shape with maximum values at both the smallest and the largest particle size ranges: 1.16×10−4 m s−1 for 4.698–9.647 μm and 0.6×10−4 m s−1 for 0.02–1.00 μm. The lowest deposition velocity was 0.31×10−4 m s−1 (0.542–0.777 μm) that was about four times less than the maximum deposition velocity.