An accurate picture of the depth and the dynamics of the planetary boundary layer (PBL) is essential to interpreting trends in atmospheric composition measurements and calculating surface concentrations of pollutants. The PBL height, however, is difficult to measure, and methods to calculate it are inconsistent across models. Petra will present a novel method for determining the PBL height using Doppler lidar data collected by the Southern Ontario Lidar Network (SOLID), focusing on the Study of Winter Air Pollution in Toronto (SWAPIT) measurement campaign as a case study.