Lagrangian modeling of the particle residence time in indoor environment

This study develops a new methodology to investigate the particle residence time in indoor environment with the Lagrangian modeling. So far, the particle residence time has been only developed in terms of the Eulerian-based advection-diffusion approach, which is easy to use but is only valid for the transport of fine, neutrally buoyant, non-inertial particles that exactly follow indoor airflows. However, for practical indoor air pollution problems, there exists a wide range of particle sizes. To extend the engineering application range of the particle residence time, a new Lagrangian-based approach, which adopts the kernel concentration estimation method, is herein proposed to model the particle residence time in indoor environment. This new approach can transfer Lagrangian particle trajectories into an Eulerian form of particle concentrations at a given point, and thus provide the mean particle residence time. The commonly used Eulerian-based advection-diffusion approach is also considered for numerical comparison. Two representative particle sizes of 10-μm coarse particles and 1-μm fine particles are input into the two approaches to investigate the effect of particle size on the mean particle residence time. The simulated results indicate that this new Lagrangian approach can give more reasonable prediction on the particle residence time than the Eulerian-based advection-diffusion approach.