An unaccounted pathway for rapid aging of atmospheric soot
Alexei F. Khalizov, Ella V. Ivanova, Egor V. Demidov, Ali Hasani, Jeffrey Curtis, Nicole Riemer, Gennady Y. Gor
AGU, Oral presentation, 2024
Abstract
Soot comes from a variety of combustion sources, and once in the air, soot particles travel over long distances, undergoing significant processing, which alters their composition, properties, and impacts. Processing can increase the soot toxicity and it also significantly alters the soot climate warming potential, which is highly sensitive to particle morphology and composition. Although soot particles are fractal aggregates, in atmospheric aerosol models they are commonly represented as spheres. Previously, using laboratory experiments, we have shown that owing to fractal morphology, soot particles rapidly acquired small amounts of condensate upon exposure to the trace gas chemicals similar to those co-released during combustion or generated by photochemical oxidation. If water-soluble, these chemicals even in minute amounts drastically improved the wettability of soot, promoting capillary condensation of water vapor, as manifested by significant soot particle compaction upon humidification. Our kinetic model for capillary condensation of trace gas chemicals and water vapor on fractal soot aggregates successfully supported these experimental observations. To assess the role of capillary condensation in the aging of soot in the atmosphere, we extended our model towards multi-component trace vapors. Here, we will show how this new multi-component capillary condensation model (MCCCM) was employed in conjunction with the particle-resolved PartMC-MOSAIC aerosol model to explore relevant scenarios for atmospheric aging of fractal soot. The results suggest that in a non-polluted environment, capillary condensation alone can rapidly transform hydrophobic soot particles into cloud condensation nuclei. Furthermore, we observe significantly different responses between fractal and spherical soot particle implementations in the model towards changes in atmospheric trace gas vapor supersaturations caused by variations in air temperature and photochemical activity. We conclude that capillary condensation represents an important mechanism of atmospheric soot aging and must be incorporated into atmospheric aerosol models to improve their predictive power.