WRF Simulations of Passive Tracer Transport from Biomass Burning in South America: Sensitivity to PBL Schemes

The Weather Research and Forecasting (WRF) model is used to study the transport of a passive scalar plume, representing smoke from biomass burning in South America (SA). In this context, the Mellor–Yamada–Nakanishi–Niino (MYNN), Yonsei University (YSU), and Bougeault-Lacarrere (BouLac) Planetary Boundary-Layer (PBL) schemes were utilized. A total of three simulations were conducted, one for each PBL scheme, starting on August 15, 2019, and ending on August 20, 2019. This period was characterized by a high concentration of smoke, which were transported to the southern and southeastern regions of South America. During this period, the direct impact of these particulates was observed in the São Paulo Metropolitan Area (SPMA). To determine the positions of the passive tracers, data from the Fire Information for Resource Management System (FIRMS) were used to identify the regions with the highest Fire Radiative Power (FRP) during the study period. Based on this analysis, three locations in different areas were selected. To analyze the transport, synoptic fields were examined during the study period to provide a better description of the atmospheric dynamics. On the mesoscale, the impact of diffusivity was assessed for each PBL scheme. For validation, surface data from the Light Detection and Ranging (LiDAR) system, located in the São Paulo region was utilized. It was observed that one of the tracers reached the SMPA in all three simulations. However, when analyzing the other tracers, the BouLac scheme failed to transport the particulates to this region. Dynamically, the low-level jet played an active role in transporting the tracers across the southern part of domain and subsequently toward the southeastern region.