Physical and Optical Properties of Black Carbon from Biomass Burning

Description

Black carbon (BC) is considered the 2nd most important global warming factor behind CO2 (Bond et al., 2013). ~50% of BC is from biomass burning (BB), estimated at up to ~0.6 W/m2 atmospheric warming. Uncertainties exist due to BC morphology and mixing state. Core-shell BC is expected to enhance absorption by up to a factor of 2. Therefore, it is important to characterize the morphology of BC and isolate the absorption from the BC-containing particles as BC is often mixed in BB plumes with species that also absorb sunlight, e.g. Brown carbon. Direct on-line measurements of BC are made with the single particle soot photometer (SP2) from fresh, aged, and laboratory BB to investigate the presence of a coating enhancement or not (Cappa et al., 2012). We also present quantitative results from a BC removal technique with the SP2 that could be implemented similarly to the thermal denuder (Huffman et al., 2009). BC in concentrated BB plumes from the two largest wildfires in New Mexico’s history are compared with BC from indoor generation from single-source fuels, e.g. ponderosa pine, sampled during Fire Lab At Missoula Experiments IV (FLAME-IV). FLAME-IV includes direct emissions, well-mixed samples, and aging studies. Las Conchas Fire (2011) BC was sampled after only a few hrs of aging and exhibits mostly core-shell structure (China et al., 2013). Whitewater Baldy Fire (2012) BC was sampled ~10-20 hrs and includes partially coated BC and thick coated core-shell BC. Ambient measurements are compared with direct lab emissions to understand BC aging to improve model treatment of BC absorption in GCMs. The addition of preliminary BB data from the ARM MAOS in GoAMAZON IOP (Feb – Mar 2014) will be included if possible. Removal of Aquadag, a BC surrogate, with an SP2 was quantified with a 2nd SP2 and a photoacoustic soot spectrometer (PASS-3). The average percent removed of monodisperse samples by mass and number of the original size are 88.9% ± 18.6% and 87.3% ± 21.9%, respectively, demonstrating large-scale removal of Aquadag with the SP2. Removal is efficient for particles >100 nm dme, however, the removal of particles ≤ 100 nm dme is less efficient, and applications focused on LAC/BC in that size range might require additional techniques to improve the method. The results reported in this novel application of LII affect other instruments employing internal LII, e.g. the Soot Particle Aerosol Mass Spectrometer (SP-AMS).