A sectional aerosol model for submicron particles in indoor air.

Objectives: This study attempted to simulate indoor concentrations and the indoor-to-outdoor (I:O) number concentration ratios of aerosol particles in the submicron size range.

Methods: The developed model used size-segregated outdoor number concentrations of particles as inputs and produced the indoor aerosol size spectrum. It covered all the major dynamic processes associated with the indoor aerosol concentration: transport and filtration in the air exchange system, deposition, coagulation, nucleation, condensation, and indoor sources. The model results were compared with measured particle concentrations. Numerous sensitivity analyses were also made for testing the effect of different dynamic processes on the model results. No indoor particle sources were considered in the sensitivity simulations.

Results: Changes in the air exchange rate had the strongest effect on the simulated I:O ratios of particle number concentrations. Filtration in the air exchange system also had a large effect on the indoor concentrations. Deposition did not significantly change the particle number concentrations within a realistic range of turbulence intensity indoors and the temperature differences between the ambient air and surfaces. Coagulation affected only the smallest particle size ranges. Condensation and nucleation had potentially large effects on the particle size spectrum.

Conclusions: The model reproduced the measured I:O ratios of fine and ultrafine particle concentrations with reasonable accuracy. The model can be a valuable tool with which to estimate the I:O ratios for human exposure assessment.