Analysis of pollutant transfer from outdoor to indoor environment through decoupled numerical approach and experiment: Case study of a Paris apartment with shear-induced natural ventilation

Natural ventilation is widely used for air renewal, but in polluted areas it can favor the entrance of outdoor traffic-related pollutants into the indoor environment. In this article, the first goal is to propose an operational and adapted decoupled Computational Fluid Dynamics (CFD) approach for shear-induced ventilation configurations, which are common in dense urban areas. Simulations at the district and at the apartment scales are performed separately, and a small additional computational domain at the inlet window is introduced into the indoor simulation. The second goal is to study the transfer of outdoor traffic air pollution into the interior of a real Haussmann-style Parisian apartment. Full scale measurements were conducted to investigate overall trends of pollutant concentration at some points inside the apartment, followed by detailed analysis of the pollutant transfer between outdoor and indoor with CFD simulations. The accuracy of CFD was evaluated by comparing with measurements, i.e. 3D anemometer and NO 2 microsensors outputs. The detailed CFD space-time evolution map indicated that outdoor pollutants, once entering indoors, are transported mainly along the room perimeters, causing concentration to start to rise from the perimeters toward the room centers. CFD simulations are most useful during the first 15 minutes after the window is opened, because after that the NO 2 concentration reaches a stable and uniform level in the apartment, comparable to the outdoor NO 2 concentration. The 15 min limit corresponds to the apartment mixing time. Finally, these results provide better understanding of outdoor/indoor pollutant transfer under natural ventilation conditions in real urban areas. • Outdoor/Indoor transfer of NO2 pollutant is analyzed in an apartment. • Adapted decoupled CFD approach is applied to shear-induced natural ventilation. • CFD simulations are compared with full-scale field measurements. • Time evolution analysis reveals how outdoor pollutants propagate indoors. • After 15 min of natural ventilation, indoor NO2 concentration is almost homogeneous.