Constraining the Particle-Scale Diversity of Black Carbon Light Absorption using a Unified Framework

PAYTON BEELER, Rajan K. Chakrabarty, Washington University in St. Louis

     Abstract Number: 279
     Working Group: Aerosol Physics

Abstract
Atmospheric black carbon (BC) manifests across a wide spectrum of morphologies and compositional heterogeneity. The distribution of BC among diverse particles of varied composition gives rise to enhancement of its light absorption capabilities by over twofold in comparison to that of pure BC. This situation has challenged the modeling community to consider the full complexity and diversity of BC on a per-particle basis for accurate estimation of its light absorption. The conventionally adopted core-shell approximation is inadequate in not only estimating but also capturing absorption trends for ambient BC. Here, we develop a unified framework which accounts for the complex diversity in BC morphology and composition using a single metric, the phase shift parameter (ρ_BC). We systematically investigate the effect of variations in ρ_BC across the multi-space distribution of BC morphology, mixing-state, and mass as reported by field and laboratory observations. We formulate universal scaling laws centered on ρ_BC and provide physics-based insights regarding overestimation of BC light absorption by core-shell approximations. We conclude by packaging our framework in an open-source Python application to facilitate community-level use in future BC-related research. Our framework thus provides a computationally inexpensive source for calculation of absorption by BC, and can be used to constrain light absorption throughout the atmospheric lifetime of BC.