Mass-transport aspects of pollutant removal at indoor surfaces

The mass-transport-limited rate of pollutant deposition onto indoor surfaces is examined in this paper. Transport of both particles and highly reactive gases through the boundary layer of air adjacent to a surface is analyzed for three model airflow conditions: (1) natural convection flow along room surfaces, (2) forced laminar flow parallel to room surfaces, and (3) homogeneous turbulence in the core of the room. Transport mechanisms considered include convective diffusion, thermophoresis, and gravitational sedimentation. The predicted mass-transport-limited deposition velocity, averaged over the surfaces of a room, varies from order 10^(−6) to 10^(−2) m s^(−1) over the range of pollutant diffusivities and particle sizes encountered. Theoretical predictions are in rough agreement with the limited experimental data that have been taken inside rooms. Results show that if buildings were designed and operated such that natural convection of forced laminar flow conditions prevailed with surface temperatures a few degrees K warmer than the room air, soiling of vertical surfaces due to deposition of soot particles in the size range 0.1–1 μm diameter could be greatly reduced