AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Impact of Hygroscopicity and Refractive Index of Black Carbon Coatings on Absorption Enhancement
LAURA FIERCE, Francisco Mena, Tami Bond, Nicole Riemer, University of Illinois at Urbana-Champaign
Abstract Number: 683 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Absorption by black carbon (BC) is enhanced when BC is mixed with non-absorbing aerosol components. Modeled absorption by a BC-containing particle depends on the volume of the BC core, the volume and composition of the coating material, and the assumed particle configuration. The size and composition of fresh BC-containing particles vary between emission sources and are modified after emission by condensation of semi-volatile substances and coagulation with other particles, so absorption by atmospheric BC depends on the characteristics of fresh BC-containing particles and the processes that affect them after emission.
In this study, we simulated the evolution of aerosol emissions in an urban area with the particle-resolved model PartMC-MOSAIC and evaluated the sensitivity of absorption enhancement by BC-containing particles to the hygroscopicity and refractive index of non-BC components. We evaluated BC absorption as a function of relative humidity and wavelength, considering two assumed particle configurations: the core-shell approximation and the dynamic effective medium approximation. For both optical configurations, we show that the sensitivity of BC absorption to particle composition depends strongly on the ambient relative humidity. At high relative humidity, absorption by black carbon is highly sensitive to the hygroscopicity of the dry aerosol coating and is insensitive to the coating refractive index. At low relative humidity, absorption is insensitive to particle hygroscopicity but sensitive to the refractive index of the dry coating.