Effects of Room Furnishings and Air Speed on Particle Deposition Rates Indoors

Particle deposition to surfaces plays an important role in determining exposures to indoor particles. However, the effects of furnishings and air speed on these rates have not been well characterized. In this study, experiments were performed in an isolated room (volume=14.2 m³) using three different indoor furnishing levels (bare, carpeted, and fully furnished) and four different air flow conditions. Deposition loss rates were determined by generating a short burst of polydispersed particles, then measuring the size-resolved (0.5–10 μm) concentration decay rate using an aerodynamic particle sizer. Increasing the surface area from bare (35 m² nominal surface area) to fully furnished (12 m² additional surface area) increased the deposition loss rate by as much as a factor of 2.6 with the largest increase seen for the smallest particles. Increasing the mean airspeed from <5 to 19 cm/s, by means of increasing fan speed, increased the deposition rate for all particle sizes studied by factors ranging from 1.3 to 2.4 with larger particles exhibiting greater effects than smaller particles. The significant effect of particle size and room conditions on deposition loss rates argues against using a single first-order loss-rate coefficient to represent deposition for integrated mass measurements (PM_2.5 or PM₁₀).