AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
On the Density and Homogeneous Internal Composition of Brown Carbon Spheres from Biomass Burning
Bongjin Seo, Christopher Oxford, BENJAMIN SUMLIN, Robert Pattison, Brent Williams, Rajan Chakrabarty, Washington University in St. Louis
Abstract Number: 699 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Recent observations have provided strong evidence for brown carbon (BrC) to impact global climate change by radiative forcing. BrC aerosols produced from biomass burning strongly absorb light in the near-ultraviolet wavelengths. Not much is known about the densities of BrC aerosols that dictate their atmospheric movement, especially, when considering the influence of combustion temperature and fuel type. Here, we measured the effective density of nascent BrC spheres emitted from smoldering combustion of Alaskan peatlands using a differential mobility analyzer (DMA), a centrifugal particle mass analyzer (CPMA), and a condensation particle counter (CPC) system. The DMA selected monodisperse BrC particles based on their mobility diameters, and the particles were classified by the CPMA as a function of their individual masses. CPC determined the number concentrations of particles from the CPMA. The effective density and mass-mobility exponent were calculated with the mobility size selected by the DMA and the particle mass measured by the CPMA and CPC. The particle effective density of nascent particles ranged from 0.85 to 1.19 g cm-3 with increasing smoldering temperatures from 180 to 360 °C. We observed a critical combustion temperature of approximately 240 °C above which pyrolysis mechanisms begin to influence particle properties. The calculated mass–mobility exponent was a constant 3.0 confirming the spherical shape of these aerosols. Then, a volatility tandem differential mobility analyzer (V-TDMA), by replacing the DMA, was used to volatilize the organic matter constituting these particles. The effective density of particle phase mass remaining after thermal volatilization was confined to a narrow range between 0.9 and 1.1 g cm-3. These findings show a homogeneous internal composition for these particles.