Indoor Deposition and the Protective Effect of Houses against Airborne Pollution

The protective value of a house during a release of toxic materials has been investigated to the atmosphere. A review of the relevant literature revealed wide agreement on dose reduction factors from 0.5 to 0.2. According to the literature indoor deposition rather than filtration by the building envelope was the main cause of the reduction, but very little information on indoor deposition exists.

The main topic for this work has been the measurement of indoor deposition using monodisperse particles in the size range 0.5 to 5.5 #mu#m, labelled with neutron activable tracers. The decay of aerosol concentration was measured and average deposition velocities were recorded in four houses. The results were consistent with increasing deposition velocities for increasing particle size and increasing degree of furnishing.

Neutron activable particles have been used for measurements of skin deposition velocities to a human volunteer. The deposition velocity was found to be 7.4#+-#1.1 x 10"-"4 ms"-"+ for the 0.5 #mu#m particles and 57"+-"14 x 10"-"4 ms"-"1 for the 2.5 "mu"m particles. These values of skin deposition velocities imply that the amount of pollutants deposited to the skin of a dressed person is more than an order of magnitude larger than the amount deposited in the lungs, and that skin deposition is an important pathway for toxics that can penetrate through the skin.

Beryllium-7 was used as a tracer in a series of experiments. The activity distribution of this isotope was determined using a Berne low pressure impactor. Median diameters ranged from 0.7 to 1.1 #mu#m and it was found that the activity distribution followed the mass distribution of the accumulation mode for atmospheric particles.

I/O measurements have been made with two impactors. The results showed that the reduction in indoor air concentration was largest for supra micron particles. (au) 26 tabs., 46 ills., 87 refs..