Comparison of the modelling and the experimental results on concentrations of ultra-fine particles indoors

This paper describes a dynamic method for estimating particle number concentrations indoors. In order to predict the variations of concentrations, a number balance model has been developed. In the model, the total number concentration of particles with sizes from 0.01 to larger than 1 μm was used. The model was validated with experimental data obtained at different measurement locations in Sweden, and the results revealed very good agreement between predicted and measured concentrations. The study showed that this method is a good tool for predicting the number of concentrations of ultra-fine particles (NCUFPs) indoors. If combined with the measurement results even weak indoor sources can be identified, which might be very difficult with a purely experimental technique. The method can also be used to analyze particle removal from the indoor air by mechanisms other than ventilation (sink effects). In addition, the model simulations suggest that at relatively high outdoor concentrations, temporarily lower air change rates could be employed in order to decrease the concentrations of ultra-fine particles indoors. The study revealed that such ventilation strategy might be applicable in buildings without strong indoor sources (e.g. offices).