American Association for Aerosol Research - Abstract Submission

AAAR 36th Annual Conference
October 16 - October 20, 2017
Raleigh Convention Center
Raleigh, North Carolina, USA

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Black Carbon Characterization in Aged Wildfire Plumes Observed at the Mt. Bachelor Observatory

JAMES LAING, Daniel Jaffe, Arthur J. Sedlacek, University of Washington, Bothell, WA, USA

     Abstract Number: 154
     Working Group: Carbonaceous Aerosols in the Atmosphere

Abstract
Black carbon (BC) is the predominant light-absorbing aerosol constituent in the atmosphere and one of the largest sources in biomass burning. To better understand BC in biomass burning plumes a Single-Particle Soot Photometer (SP2) was deployed at the Mt. Bachelor Observatory (MBO, 2.7 km a.s.l.) in Central Oregon during the summer of 2016. The sampling site offers the observation of aged wildfire plumes transported in the free troposphere. The SP2 measures refractory black carbon (rBC) mass concentration and rBC number size distribution. Additional measurements at MBO included CO, CO2, O3, aerosol three wavelength scattering coefficients (σscat), PM1 mass, and total aerosol size distribution. Two instruments measuring aerosol absorption coefficients (σabs) were deployed; the 3-wavelength Tricolor Absorption Photometer (TAP) and 7-wavelength Aethalometer (AE-33).

Wildfire smoke from the Gap Fire in Northern California was observed at MBO over three days in late August. Thirteen individual plumes were identified. The plumes were transported 10 to 15 hours from emission to observation at MBO. All plumes had high single scattering albedos (0.96-0.97) and absorption Ångström Exponent (AAE) values (2.23-2.85). ΔrBC/ΔCO enhancement ratios for these plumes ranged from 2.57 to 5.31 ng m3 ppbv-1 and rBC fraction of PM1 (ΔrBC/ΔPM1) ranged from 0.76 to 1.37%. The geometric mean diameter (GMD) of the BB plumes size distributions ranged from 132 to 194 nm, and were proportional to plume concentration (i.e. σscat, PM1).

As the aerosol are highly scattering (SSA ~ 0.97), the absorption coefficients measured by the Aethalometer are significantly influenced by scattering corrections. Using scattering corrections Arnott et al. (2005) and Schmid et al (2006) in addition to the Aethalometers dual-spot filter-loading compensation parameter reduced σabs significantly across all wavelengths. Despite this, the σabs from the Aethalometer were 20 to 40% higher compared to the TAP. A detailed evaluation and comparison of aerosol absorption measurement correction schemes will be made as well as comparisons estimated BC (eBC) derived from the absorption measurements and rBC.