10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Scaling Laws for Light Absorption by Atmospheric Black Carbon Aerosol
RAJAN K. CHAKRABARTY, William Heinson, Washington University in St. Louis
Abstract Number: 1664 Working Group: Aerosol Physics
Abstract Black carbon (BC) aerosol, the strongest absorber of visible solar radiation in the atmosphere, contributes to a large uncertainty in direct radiative forcing estimates. A primary reason for this uncertainty is inaccurate parameterizations of BC mass absorption cross-section (MACBC) and its enhancement factor (EMACBC)–resulting from internal mixing with non-refractory and non-light absorbing materials such as sulfates, nitrates, and organic carbon–in climate models. Electromagnetic wave interaction with BC aerosol is a complex problem involving the non-Euclidean particle morphologies that dynamically change with variations in mixing states. Here, applying scaling theory to numerically-exact electromagnetic calculations of simulated BC particles and observational data on BC light absorption, we show that MACBC and EMACBC evolve with increasing internal mixing ratios in simple power-law exponents of -1/3. Remarkably, MACBC remains inversely proportional to wavelength at any mixing ratio. When mixing states are represented using mass-equivalent core-shell spheres, as is done in current climate models, it results in significant under prediction of MACBC. We elucidate the responsible mechanism based on shielding of photons by a sphere’s skin depth. Together, our results hold promise for accurately and inexpensively parameterizing the non-equilibrium process of BC light absorption in models and satellite retrieval algorithms.