Numerical generation and coating of single soot nanoparticles: implications for atmospheric aging

The adverse effects due to the release of black carbon-based nanoparticles in the atmosphere represent the second anthropological cause of global warming and constitute one of the largest uncertainties in climate modeling. The lifecycle of such particles is complex: the freshly emitted soot ages over a timescale of minutes to days via condensation and coagulation of weakly absorbing organic aerosols. The transport, interaction with clouds, and the induced radiative forcing directly depend on the morphological and optical properties of these coated nanoparticles. This work proposes a standalone model that generates bare and coated aggregates, and measures their morphological and transport-derived properties, as well as providing an interface for optical modeling. The model is applied to atmospheric aging of soot with water, sulfuric acid, or p-xylene coatings. Both partially and fully coated particles show enhanced absorption, scattering, and single scattering albedo at mid-visible wavelength. These values are maximum for fully encapsulated aggregates. A quasi linear relationship is found between the mass absorption cross-section fraction (fMAC) and the aerodynamic growth factor. Furthermore, fMAC is higher for aggregates composed of polydisperse primary particles. Other key parameters investigated include the coating material and its partitioning, the morphology of the aggregate (fractal parameters, size, overlap) and the incident wavelength.