Mass and Number Size Distributions of Refractory Black Carbon (rBC) in
Snow and Firn Samples from Pine Island Glacier, West Antarctica
Abstract
An extended-range Single-Particle Soot Photometer (SP2) coupled to a
Marin-5 nebulizer was used to measure the refractory black carbon (rBC)
mass and number size distributions in 1004 samples from a West
Antarctica snow/firn core. The SP2 was calibrated using Aquadag and a
Centrifugal Particle Mass Analyzer for BC particles ranging from 0.5 to
800 fg. Our results from 1.03 x 10 particles indicate a significant
contribution of rare, large particles of mass-equivalent diameter (D)
> 500 nm to the total rBC mass (36%), while small
particles (D < 100 nm) are abundant but contribute <
8% to total rBC mass. We observed a mass median diameter (MMD) of 160
nm, smaller than reported for snow comparing to other regions of the
globe, but similar to East Antarctica rBC size distributions. In
addition, we observed a secondary mode at 1880 nm, possibly originated
from a combination of rBC aging processes in the atmosphere and particle
agglomeration during snow formation/deposition. We compared two sets of
samples from different seasons (wet vs. dry), and observed different
contributions of large particles to the total rBC mass of each.
Particles with D > 500 nm contributed 45% and 33% of the
total rBC mass for the wet and dry season, respectively, indicating that
larger particles are more common during the wet season.
Post-depositional processes (millimeter thick melt layers) have been
observed in some samples, although they did not change the observed
median diameter. This study provides the first detailed rBC size
distribution from West Antarctica.