Development and validation of a dynamic mass-balance prediction model for indoor particle concentrations in an office room

Abstract

The Korean government recommends intermittent operation of air purifiers (APs) as a measure to maintain indoor particulate matter (PM) concentrations below the mandatory standards and reduce exposure to indr PM_2.5 (PM with a diameter smaller than $2.5\mu \text{m}$). However, there is no guideline to inform occupants of when and how long APs should be operated to comply with the standards. In this study, we developed a dynamic mass-balance model to predict indoor PM concentrations in an office considering penetration of outdoor particles, change in number of occupants, and operational status of the AP. The model fit and prediction accuracies were verified using the American Society for Testing and Materials (ASTM) D 5157 criteria and the k-fold validation technique. We observed that indoor PM_2.5 concentrations were determined by infiltration of outdoor PM_2.5, and indoor generation/resuspension by occupants and removal. For ${\text{PM}}_{2.5-10}(2.5\mu \text{m}<\text{diameter}<10\mu \text{m})$, the indoor concentrations were determined by interior door access and indoor generation/resuspension. The operation of an AP effectively decreased indoor PM_2.5 concentration but not PM_2.5-10. We found that our model accurately predicted indoor PM concentrations. Therefore, using the developed model, a guideline may recommend: 1) start the AP when the predicted indoor PM_2.5 concentrations under no AP operation approached the standard (e.g., 90% of the standard); and 2) stop the AP when the indoor PM_2.5 concentration predicted under the assumption of no AP operation fell below the standard (e.g., 80% of the standard).

Keywords: Air purifier; I/O ratio; Infiltration factor; Particulate matter; Penetration factor; Prediction model.