10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Inter-Comparison of Techniques for the Measurement of Black Carbon from Biomass Burning: Influence of Optical and Chemical Properties
HANYANG LI, Kara D. Lamb, Joshua P. Schwarz, Vanessa Selimovic, Robert J. Yokelson, Gavin McMeeking, Andrew May, The Ohio State University
Abstract Number: 873 Working Group: Carbonaceous Aerosol
Abstract Biomass burning is a major contributor to global black carbon (BC) emissions. However, the exact magnitude of BC emissions from biomass burning is difficult to examine due in part to highly variable combustion conditions and irregular spatiotemporal repeatability (e.g., wildfire emissions do not follow a regular weekly pattern throughout the year). An additional complication is that there are many approaches that can be used to measure BC emissions. Predominant methods in use today represent one of three distinct operationally-defined quantities: “equivalent” BC (eBC), “refractory” BC (rBC), and elemental carbon (EC). Given that EC might be used to represent eBC or rBC, and vice versa, it is essential to understand the relationship among BC measurements, and develop robust BC emission factors for biomass burning.
To systematically assess BC measurement techniques and investigate the uncertainties of BC emissions from biomass burning, we participated in the Fire Sciences Laboratory studies in Missoula, MT during Autumn 2016 as part of the Fire Influence on Regional and Global Environments Experiment (FIREX). Eight real-time instruments were deployed sharing the same smoke inlet, including two in situ methods for eBC, five filter-based methods for eBC, and one method for rBC; furthermore, quartz filters were collected for off-line thermal-optical analysis of EC. There have been similar prior efforts, but none that focused on biomass burning smoke have been this comprehensive (and none have compared EC and rBC). This presentation extends our previous work to compare EC with light-absorption measurements of BC. Quartz and quartz-behind-Teflon® filter samples containing EC and OC are analyzed using Sunset Laboratory OCEC analyzer by IMPROVE-A temperature protocol. Such filter data is also used to calculate organic aerosol concentration (COA), bare-quartz organic mass (OM) and particle-phase organic mass fraction (XP), and thus we can evaluate the effect of OA gas-particle partitioning on emission factors of BC.
In our presentation, the association between BC uncertainties and intercorrelated optical and chemical properties of biomass burning (e.g. single scattering albedo, angstrom absorption exponent, absorption enhancement, COA, and OC/EC ratio) will be illustrated using both statistical methods and an alternative graphical/parametric approach. Our results indicate that both fixed and proportional biases are present among instruments. Fixed biases exist when comparing three general BC techniques (as well as various instruments using the same measurement technique). Measurements of BC may be also biased either high or low depending on aerosol properties and OA gas-particle partitioning, which is classified as proportional biases. This work will encourage accurate quantification of BC emissions from biomass burning and improve the predictions of climate and chemical-transport models.