Black carbon aerosol optical properties are influenced by initial mixing state

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Megan D Willis1, Robert Michael Healy2, Nicole Riemer3, Matthew West4, Jonathan M Wang2, Cheol-Heon Jeong2, John Wenger5, Jonathan Abbatt1 and Alex Lee2, (1)University of Toronto, Department of Chemistry, Toronto, ON, Canada, (2)University of Toronto, Toronto, ON, Canada, (3)University of Illinois, Atmospheric Sciences, Urbana, IL, United States, (4)University of Illinois at Urbana Champaign, Mechanical Science and Engineering, Urbana, IL, United States, (5)University College Cork, Cork, Ireland
Incomplete combustion emits teragram quantities of black carbon (BC) aerosol to the troposphere each year, resulting in a significant warming effect on climate that may be second only to carbon dioxide. The magnitude of BC impacts on a global scale remains poorly constrained and is intimately related to its particle-scale physical and chemical properties. Using particle-resolved modeling informed by novel quantitative measurements from an Aerodyne soot-particle aerosol mass spectrometer (SP-AMS), we show that initial mixing state (or the distribution of co-emitted components amongst fresh BC-containing particles) significantly affects BC-aerosol optical properties even after a day of atmospheric processing. Both single particle and ensemble observations indicate that BC near emission co-exists with hydrocarbon-like organic aerosol (HOA) in two distinct particle types: HOA-rich and BC-rich particles. The average mass fraction of black carbon (mfBC) in HOA- and BC-rich particle types was 0.02-0.08 and 0.72-0.93, respectively. Notably, positive matrix factorization (PMF) analysis of ensemble SP-AMS measurements indicates that BC-rich particles contribute the majority of BC mass (> 90%) in freshly emitted particles. This new measurement capability provides quantitative insight into the physical and chemical nature of BC-containing particles and is used to drive a particle-resolved aerosol box model. Significant differences in calculated single scattering albedo (an increase of 0.1) arise from accurate treatment of initial particle mixing state as compared to the assumption of uniform aerosol composition at the point of BC injection to the atmosphere.