AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Tar Ball Aggregates in the Plume of the Whitewater-Baldy Complex Wildfire, NM
Giulia Girotto, Swarup China, Janarjan Bhandari, CLAUDIO MAZZOLENI, Barbara Scarnato, Kyle Gorkowski, Allison Aiken, Manvendra Dubey, Michigan Technological University
Abstract Number: 423 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Atmospheric tar balls (TBs) are carbonaceous particles abundant in slightly aged biomass burning smoke. TBs are currently defined based on their properties as measured under an electron microscope. These particles are almost perfectly spherical in shape and amorphous in structure, they are composed mostly of carbon and oxygen, they are resistant to the electron beam and they have typical sizes in the range of ~100 to 300 nm. Previous studies found that TBs absorb sunlight, although their optical properties are still debated, and published values especially for the imaginary part of the index of refraction are sparse and span three orders of magnitude. Because of their variable optical properties and concentrations, their radiative effects are highly uncertain.
In 2012, aerosol samples from the Whitewater-Baldy Complex (WB) fire plume were collected at the Los Alamos National Laboratory. The WB fire is to date, the largest wildfire in New Mexico’s history. The plume traveled to the sampling site over a period of a few hours (~7-8). Using scanning electron microscopy we observed that TBs were the most abundant particles in the plume (~81%, by number). In previous studies on biomass burning smoke, TBs have been typically found to be externally mixed and separated from each other; however, in our samples, we observed a significant fraction of TBs aggregates (~27% by number). We analyzed the morphological characteristics of these TB aggregates and found that they follow a scale-invariant power law similar to that of soot particles with comparable fractal dimension, despite the considerably larger size and a smaller number of the monomers. We then used this morphological information to estimate the effect of aggregation on the optical properties of these particles using numerical simulations. We will discuss these findings and implications on the potential radiative effects of biomass burning.