Understanding the Contributions of Medium- and Long-range Atmospheric Transport of Biomass Burning to Organic Aerosols in Bogotá, Colombia

RICARDO MORALES BETANCOURT, Fernando Garcia-Menendez, Karen Ballesteros, Amy P. Sullivan, Universidad de los Andes

     Abstract Number: 440
     Working Group: Biomass Combustion: Outdoor/Indoor Transport and Indoor Air Quality

Abstract
Recent field campaigns and modeling studies in Colombia have demonstrated the presence of a large Organic Aerosol (OA) fraction in urban and rural aerosols, a portion of which is due to transport of regional Biomass Burning plumes. In this work we focus on understanding the sources associated with OA and its precursors over the city of Bogotá, Colombia. We used WRF-Chem chemical transport model to investigate the contributions from medium- and long-range transport of biomass burning plumes towards the city of Bogota. To that end, we carried out regional-scale simulations with two different chemical mechanisms and aerosol schemes, RACM/MADE-VBS and MOZART/MOSAIC. Sensitivity simulations were also carried out were the influx of BB plumes at the outermost domain boundary were removed. Modeling results were compared to detailed in-situ aerosol chemical speciation data and continuous Brown Carbon and Black Carbon observations. Simulations were set-up for periods of high biomass burning (BB) activity (January-March) and a low BB activity (July-September) during 2018. We demonstrate that long-range transport of BB emissions from Northern Amazonia can episodically increase aerosol loading during September, while BB activity in the Grasslands of the Orinoco River Basin are the main source during January to March. The two aerosol schemes utilized in this work reproduce the observed seasonal variations in total fine aerosol concentration, with a difference between high- and low- BB sesasons of 10 μg/m³. The comparison between aerosol schemes showed that MOZART/MOSAIC consistently predicts more OA with a larger SOA:OA ratio than in the RACM/MADE-VBS experiment. SOA dominates the OA fraction by 66% for RACM/MADE-VBS and 74% for MOZART/MOSAIC during February and 69% for RACM/MADE-VBS and 71% for MOZART/MOSAIC during September. These differences between organic aerosol burden between the mechanisms used in this study may be attributed to the different treatment of SOA gas/particle partitioning in the schemes. During both periods, the simulation in which boundary influx was removed showed nearly 1.2 μg/m³ lower SOA, suggesting that precursors from long-range transport can substantially impact OA concentrations in the city.