AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Enhanced Light Absorption and Wavelength Dependency Due to Coating and Mixing States of Black Carbon
RIAN YOU, James Radney, Christopher Zangmeister, Michael Zachariah, University of Maryland
Abstract Number: 713 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Black carbon (BC) can warm the atmosphere through absorption of solar radiation. Internal mixing of BC with other aerosol materials has been previously shown to enhance the magnitude of light absorption of BC and, therefore, amplify the particles’ radiative heating potential. To investigate this effect we have measured the spectral dependence of BC particles mixed with both absorbing and non-absorbing materials. Black aqueous pigment particles are used as a surrogate for BC and ammonium sulfate and sodium chloride were used as non-absorbing coatings. The BC particles were also coated with brown carbon (BrC) to investigate the enhancement effect from a light absorbing coating. Aerosol absorption spectra were measured for particles with a ~10% mass ratio of BC, mimicking particles observed in the atmosphere. Data was collected using a photoacoustic spectrometer with a supercontinuum laser spanning lambda=500 nm to 840 nm. The size and the mass of particles were classified using differential mobility analyzer (DMA) and aerosol particle mass analyzer (APM), respectively. For clear coatings, the absorption of BC absorption cross-section is enhanced relative to non-coated particles. The enhancement is wavelength dependent, ranging from 20% to 60% and is highest at the shortest wavelength. Mixed BC/BrC particles also showed enhancements and changes in spectral shape. Using the T-matrix method we calculated the absorption of coating aggregates and successfully mapped the mixing states of coated BC. The modeling data is also consistent with findings from transmission electron microscopy.