AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Biases in Quantifying Light Absorption Enhancement for Coated Black Carbon Aerosol Using a Thermodenuder
NISHIT SHETTY, Apoorva Pandey, Wei Min Hao, Stephen Baker, Rajan K. Chakrabarty, Washington University in St. Louis
Abstract Number: 291 Working Group: Carbonaceous Aerosol
Abstract Recent observational findings suggest black carbon (BC) aerosol to primarily exist in a mixed state with organic compounds (OC). Visually, the mixed OC exists as shell coatings on BC cores (aggregates). The magnitude of light absorbed by BC aerosol gets enhanced upon internal mixing with non-absorbing and weakly absorbing OC. A thermodenuder is a widely used instrument to study the enhancement (Eabs) in BC light absorption. It operates by heating the aerosol stream to vaporize condensed organics followed by removal of the generated gas phase OC using activated carbon denuders. The magnitude of Eabs can be determined by quantifying aerosol absorption coefficients before and after thermodenuding the particle stream. Values of Eabs obtained using a thermodenuder may suffer from biases due to incomplete stripping of OC coatings and/or thermophoretic losses of particles inside the instrument. We performed experiments to investigate these biases as a function of the thermodenuding temperature for coated BC particles generated from biomass burning. The amount of BC and OC present post-thermodenuding was quantified using the IMPROVE thermal/optical reflectance method. In addition to Eabs, change in optical properties such as the single scattering albedo and Absorption Ångström Exponents were also measured with varying temperature. This presentation will conclude by summarizing the potential impacts of thermodenuder biases on BC light absorption enhancements, explain recent field observations, and provide recommendations for future research making use of this instrument.