Abstract: High concentrations of particulate matter are the biggest air pollution problem in Metropolitan Region of Aburrá Valley – Colombia (MRVA). Atmospheric contingencies episodes are continuously presented due to the emissions generated, product of population, the vehicle fleet and the industrial sector growth; to this is added its topography of a mountainous and narrow valley and the presence of meteorological phenomena that hinder the dispersion of pollutants [1]. There are records that the concentrations of this pollutant in the MRVA have exceeded by 226% the maximum permissible level established by Colombian regulations [2, 3]. Particulate matter is classified according to its size, origin and chemical composition. The most studied fraction around the world is the one below 2.5 microns (PM2.5), due to the health effects it generates. The burning of biomass represents an important source of particulate matter emissions, which is largely composed of the carbonaceous fraction, represented by organic and elemental carbon (OC and EC respectively) [4, 5]. These carbonaceous compounds have adverse effects on the environment, mainly on the climate and human health. Within biomass combustion processes,compounds such as levoglucosan, water-soluble organic carbon and water-soluble potassium are emitted, which are widely used as biomass burning tracers. Recent studies support the hypothesis of the influence of biomass burning on air quality in the study area, using satellite, statistical and modeling tools. However, experimental studies are needed to determine the characteristics of particulate matter, because given the diversity of its composition, it is important to characterize the particles that are emitted in the region, since their composition can vary spatially and temporally according to the nature of the sources [6].This study aims to identify OC, EC and tracers to estimate the contribution of biomass burning to particulate matter concentrations in the MRAV. The monitoring of PM2.5 was carried out in two campaigns in 2023, march-april and september, considered by the environmental authority as episodes of atmospheric contingency. The monitoring site is located at the center of the valley. High and low volume equipment was used, using quartz filters previously pre-baked at 550°C for 4 hours. 23 collected samples were chemically characterized for the determination of OC and EC, water-soluble organic carbon, water-soluble potassium, and other ions were quantified using analytical techniques such as inductively coupled plasma (ICP), ion chromatography, and thermo-optical methods. Morphological characterization was also performed by field emission scanning electron microscopy (FE-SEM). The results reflect that the carbonaceous fraction reaches percentages of 50% in PM2.5 and there is a significant contribution of secondary OC formation. The OC/EC ratios in the first monitoring campaign were above 2, reflecting the influence of secondary OC formation and possible contributions from biomass burning. The back trajectories show that during the march- april season, the wind plumes came from the northeastern of South America, where the greatest number of hot spots, associated with forest fires, were identified. Meanwhile, for the september season, the wind plumes came from the southeast, where the greatest number of hot spots were observed.

Keywords: Particulate matter, biomass burning, organic carbon, elemental carbon, biomass burning tracers.