A218-0005
Black carbon aerosol mixing state in fresh and aged wildfire smoke: Harmonizing Instruments, Laboratory and Field Studies
Wednesday, 16 December 2020
Poster
James Edward Lee1, Allison C Aiken2, Kyle Gorkowski3, Christian Carrico4 and Manvendra Krishna Dubey2, (1)Los Alamos National Laboratory, EES-14: Earth Systems Observations, Los Alamos, NM, United States, (2)Los Alamos National Laboratory, Los Alamos, NM, United States, (3)Los Alamos National Laboratory, Los Alamos, United States, (4)New Mexico Institute of Mining and Technology, Socorro, NM, United States
Abstract:
The mixing state of carbonaceous aerosols emitted by biomass burning determines its capacity to absorb sunlight and thus the magnitude of aerosol radiative forcing but is highly uncertain. Black carbon (BC) internally mixed with non-absorbing coating has been shown to enhance light absorption by BC (Cross 2010, McMeeking 2014) in accordance with Mie theory. However, not all laboratory studies observed this effect (McClure 2020) and results from field observations are inconsistent (Cappa 2012, Lack 2012, Liu 2015). Recently, we have shown that absorption enhancements of soot in aged wildfire plumes can be attributed to coatings and that these coatings also contain brown carbon (Lee 2020). The mixing-state as well as the morphology of BC containing aerosol and the chemical composition of BC-coatings likely account for some of this disparity. Measurements of BC mass, mixing-state and composition by combining Single-Particle Soot Photometer (SP2), Soot-Particle Aerosol Mass Spectrometer (SP-AMS), and Scanning Mobility Particle Sizer (SMPS) are powerful diagnostics to constrain this. We will resolve the disparate findings by harmoniously connecting our novel instruments in controlled laboratory burns to better understand BC coating processes in relation to its absorptive properties.
We will report on experiments that relate BC absorption enhancement and coating thickness to the mass and composition of the externally-mixed and internally-mixed BC smoke composition using a fuel relevant to the southwest US. The SP2 directly measures BC mass and coating thickness and provides information on morphology. Measurements by the SP-AMS in non-refractory (NR), NR+BC, and BC+coating modes provide independent and detailed information on bulk aerosol mass as well as coating mass and composition. Multiple laboratory burns will be used to gain this information. While past studies have shown that reproducing burns is challenging, our experiments will exploit multiple diagnostics to normalize results to assess relationships of coating composition to absorption enhancements. Results will be used to elucidate the mechanisms responsible for BC coating that we observed in the aged wildfire plume.
