Deposition, Resuspension, and Penetration of Particles within a Residence

Aerosol concentrations and particle size distributions were measured indoors and outdoors at a two-storey residence in California during the summer months. A single central sampling point in the downstairs living area was used for all indoor samples. The deposition rate for supermicron particles was measured by raising the particle concentration indoors and simultaneously measuring air infiltration rates and particle concentration decay rates. For particles between 1 and 5 μm diameter, the deposition velocity closely matched the calculated settling velocity. For particles larger than 5 μm the deposition velocity was less than the calculated settling velocity, probably due to the nonspherical nature of these particles. The penetration factor for supermicron particles, a measure of the amount of filtration achieved by the building shell, was calculated using the experimentally determined deposition velocities and indoor/outdoor particle ratios when no resuspension or generation activities were present. A penetration factor of one was found, indicating that the building shell was not effective at removing infiltrating particles. Resuspension was measured under several different conditions and was found to have a significant impact on indoor particle concentrations. Just walking into a room can increase the particle concentration by 100% for some supermicron particle sizes. For light activity with four people in the residence, a resuspension rate between 1.8 × 10⁻⁵ and 3.8 × 10⁻⁴ h⁻¹ was found for supermicron particles assuming a particle density of 1 gm⁻³. These calculated rates may be lower than the actual rates due to assumptions made about the particle size distribution of the floor dust.