AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Phase Separation Effects on the Optical Properties of Mixed Brown Carbon/Ammonium Sulfate Aerosol
JAMES RADNEY, Christopher Zangmeister, National Institute of Standards and Technology
Abstract Number: 279 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract The role of brown carbon aerosols (BrC) in the atmosphere has been a subject of strong interest in recent years. In the atmosphere, BrC is rarely pure but instead exists as a complex mixture of multiple species; the most common of which is ammonium sulfate (AS). Here, we demonstrate that the mass mixing ratio of BrC and AS significantly affects the optical properties of the resultant particle compared to what would be predicted through simple mixing or core-shell models. Relative to pure AS, small additions of BrC decrease the observed extinction cross section (Cext) by up to 20%. Above a critical mass ratio of BrC, Cext spikes to be higher than that of pure AS; further increases in BrC content further increase Cext. This decrease and subsequent increase in extinction with BrC is a direct result of changes in scattering as absorption increases monotonically with BrC content. We posit that air inclusions and are present at the phase interface of BrC and AS, in a manner similar to mixed crystals of different lattice structures, and are responsible for the observed trends.