Three-Dimensional Dynamic Monitoring of Indoor PM_2.5 with 3D I‑Lidar

Because people spend most of their time indoors, it is of particular interest to characterize the sources and spatiotemporal variations in PM_2.5 in indoor air. While indoor PM_2.5 concentrations are often measured at fixed heights, a side-scatter I-Lidar device was recently developed to profile PM_2.5 concentrations by recording light intensities scattered from a laser beam. Here, we expand the idea to dynamically monitor the three-dimensional variation in PM_2.5 in indoor air by using an array of I-Lidar devices (3D I-Lidar). The 3D I-Lidar was calibrated against transmittances along the laser beam and from the beam to camera, scattering angle, and field-measured PM_2.5 concentrations. The calibration can be simplified using an integrated equation to empirically address the influences of major parameters. The instrument was tested in two case studies to three-dimensionally and dynamically quantify the emission and dispersion of PM_2.5 from cigarette smoking and incense burning. The highly resolved spatiotemporal variations in PM_2.5 concentrations from the two sources can be well portrayed. Finally, the potential and limitations of 3D I-Lidar are discussed.