Indoor aerosol deposition studies using neutron-activatable tracers

The occupants of buildings may be exposed to a variety of particulate pollutants, which constitute a health hazard when airborne or when deposited on the internal building surfaces. In order to provide generic data for exposure evaluation, Imperial College, in collaboration with the Danish National Laboratory at Riso, have developed a method for measuring indoor aerosol deposition. Monodisperse particles are labelled with a neutron-activatable tracer, so that, when the particles are dispersed in indoor air, air filter samples can be collected for neutron activation analysis (NAA). The aerosol time decay constant can then be determined and, from that, the aerosol deposition velocity can be inferred. Full-scale experiments have been carried out in two houses: a single storey typical Danish dwelling and a centre-terraced Building Research Establishment British test house. Aerosol deposition velocities have been measured, under a variety of conditions, for two particulate sizes: 2 and 4 μm aerodynamic diameter. The experimental techniques used and the results obtained are presented. In addition, for the case of an unfurnished room, a comparison of the results obtained with the theory presented by Nazaroff and Cass (1989) is made. The results indicate that the technique is suitable for studying indoor particulate pollution cycling.