AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Fractal Morphology of Black Carbon Aerosol Enhances Absorption in the Thermal Infrared Wavelengths
WILLIAM HEINSON, Rajan Chakrabarty, Washington University in St. Louis
Abstract Number: 186 Working Group: Aerosols, Clouds, and Climate
Abstract Black carbon (BC) aerosols have been identified as major contributors to global warming and climate change. Due to their formation via Brownian diffusion in high-temperature combustion systems, these particles are emitted in the form of fractal-like aggregates of carbon spherules or monomers. The light absorbing properties of BC aggregates in the visible wavelengths are now fairly well understood and quantified. On the contrary, their absorption properties in the thermal infrared (TIR) wavelengths have been an understudied area of research. Owing to their small size parameters in the TIR wavelengths, BC aggregates are simplistically parameterized in climate models and remote sensing algorithms using the Lorenz–Mie theory for spheres. This could lead to substantial errors in atmospheric correction of remotely sensed data and estimation of absorption by greenhouse gases. We numerically calculate the mass absorption cross sections (MACs) of BC fractal aggregates in the (TIR) wavelengths. Compared to equivalent-size spheres, the MAC values of BCs show a percent enhancement of ≈150 and 400 at small and large length scales, respectively. The absorption properties of aggregates with size parameters >1 surprisingly continued to remain in the Rayleigh optics regime. We explain this phenomenon using the Maxwell–Garnett effective medium theory and the concept of phase shift parameter