Prediction of ultrafine particle concentrations in various indoor environments

The present paper describes a method for estimation of indoor concentrations of ultrafine particles based on a particle number balance model. Previously reported data from measurements of particle sink rate, particle generation rate, air filter efficiency and outdoor concentrations were used as input data. The model was used to predict indoor concentrations in various simulated residential buildings, office buildings and classrooms. Calculations were made for cases with air change rates ranging from 0.2h(-1) up to 5h(-1), and under different assumptions about the efficiency of the supply air filtration. The simulated indoor-outdoor concentration ratios deviate less than 10% from measured values. The simulations indicate that ventilation systems can be designed to reduce the indoor concentration of ultrafine particles substantially, and consequently protect the population from a potential health hazard. The model can be used to distinguish the fraction of outdoor ultrafine particles in indoor air from the fraction originating from indoor sources.