Three-Dimensional Dynamic Monitoring of Indoor PM2.5 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 PM2.5 in indoor air. While indoor PM2.5 concentrations are often measured at fixed heights, a sidescatter I-Lidar device was recently developed to profile PM2.5 concentrations by recording light intensities scattered from a laser beam. Here, we expand the idea to dynamically monitor the threedimensional variation in PM2.5 in indoor air by using an array of ILidar 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 PM2.5 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 PM2.5 from cigarette smoking and incense burning. The highly resolved spatiotemporal variations in PM2.5 concentrations from the two sources can be well portrayed. Finally, the potential and limitations of 3D I-Lidar are discussed.