Determination of and evidence for non-core-shell structure of particles containing black carbon using the single particle soot photometer (SP2)

 

Authors

Arthur J Sedlacek — Brookhaven National Laboratory
Ernie R. Lewis — Brookhaven National Laboratory
Larry Kleinman — Brookhaven National Laboratory
Qi Zhang — University of California, Davis

Category

Aerosol Properties

Description

(1a): Fraction of near-surface rBC-containing particles, Φns (red dots), and organic aerosol mass concentration determined by HR-ToF-AMS (green dots). (1b) The ratio of the mass concentrations of C2H4O2+ (m/z=60) and C3H5O2+ (m/z=73) to total organic aerosol determined by HR-ToF-AMS. In both panels shaded regions delineate plumes A and B.
The large uncertainty associated with black carbon (BC) direct forcing is due, in part, to the dependence of light absorption of BC-containing particles on the position of the BC within the particle. It is predicted that this absorption will be greatest for an idealized core-shell configuration in which the BC is a sphere at the center of the particle whereas much less absorption should be observed for particles in which the BC is located near or on the surface. However, such microphysical information on BC-containing particles has previously been provided only by labor-intensive microscopy techniques, thus requiring assumptions for radiative transfer calculations (e.g., Lorenz-Lorentz mixing rule or core-shell model). The present poster describes a novel analysis method that utilizes the temporal behavior of the scattering and incandescence signals from individual particles containing refractory BC (rBC) measured by the single particle soot photometer (SP2) to distinguish particles with rBC near the surface from those that have structures more closely resembling the core-shell configuration. This approach permits collection of a high-time-resolution data set along with better counting statistics regarding the fraction of rBC-containing particles with rBC near the surface, Φns. Application of this method on a plume containing organic aerosol markers for biomass burn reveals that over 60% of the rBC-containing particles have rBC near the surface. Such a data set will not only provide previously unavailable information to the climate modeling community, allowing greater accuracy in calculating rBC radiative forcing, but also will yield insight into aerosol processes and life cycle.