AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
New Optical Experiments "Shed Light" on Role of Particle Morphology and Chemical Composition in the Absorption Enhancement of Coated Soot Particles
LINDSAY RENBAUM-WOLFF, Andrew Lambe, Timothy Onasch, Andrew Freedman, Leah Williams, Taylor Helgestad, Christopher Cappa, Al Fischer, Geoff Smith, Swarup China, Claudio Mazzoleni, Arthur J. Sedlacek, Eleanor Browne, Gabriel Isaacman-VanWertz, Jesse Kroll, James Brogan, Yatish Parmar, Andrew Lee, Noopur Sharma, Janarjan Bhandari, John Jayne, Douglas Worsnop, Paul Davidovits, Boston College
Abstract Number: 217 Working Group: Aerosols, Clouds, and Climate
Abstract Atmospheric black carbon (BC), mostly in the form of soot particles, absorbs light and produces local heating of the atmosphere and may contribute to warming of the Earth’s climate. Models that include radiative forcing by BC assume internal mixing with non-BC aerosol components that can substantially enhance BC absorption. However, such model estimates have yet to be clearly validated by atmospheric or laboratory measurements. The extent to which absorption by BC can theoretically be enhanced via lensing depends critically on the ratio of non-refractory coating to refractory black carbon as well as on the morphology of the coated particles and the refractive index of the coating material.
To systematically examine the influence of atmospherically relevant non-refractory coatings on BC chemical composition, morphology, and optical properties, a methane diffusion flame was used to generate soot particles that subsequently entered an oxidative flow reactor. Secondary organic aerosol (SOA) and sulfuric acid coatings were produced in situ via gas phase OH oxidation of alpha-pinene, naphthalene, or SO$_2 that were added to the carrier gas flow. Absorption enhancements of up to a factor of two were observed across ten measured wavelengths ranging from 301 to 687 nm. At a specific coat:core ratio the absorption enhancement was of similar magnitude regardless of coating type, suggesting a simple parameterization for predicting absorption enhancements in ambient particles. Soot particle – aerosol mass spectrometer (SP-AMS), single particle soot photometer (SP2), and TEM results are used to elucidate how particle morphology and chemical composition govern absorption enhancement behavior.