Identifying, Quantifying, and Constraining Uncertainties Associated with Black Carbon Emissions during Open Biomass Burning

The proposed work will leverage the NOAA-organized Fire Influence on Regional and Global Environments Experiment (FIREX) campaign to study black carbon (BC) emissions from simulated Western US fires. Briefly, this work will provide a comprehensive and systematic inter-comparison of BC instrumentation. Open biomass burning is a major source of atmospheric BC, but large uncertainties exist in BC emission factors (EFBC). These uncertainties can be grouped into two categories: instrument differences and natural variability. Instrument differences are related to various techniques used to measure BC, a generic term that can represents one of three distinct operationally-defined quantities: “equivalent” BC (eBC), “refractory” BC (rBC), and elemental carbon (EC); instrument differences are especially problematic when EFBC representing eBC, rBC, and/or EC are compiled for emission inventories due to potential inconsistencies among techniques. While similar inter-comparison studies have been conducted in the past, it is unclear whether they can resolve EFBC uncertainty; they have either been conducted in controlled environments using simple systems of laboratory-generated BC or if the studies did investigate BC from biomass burning, they are not comprehensive in that they do not provide all three of eBC, rBC, and EC. Natural variability further complicates this uncertainty due to differences in EFBC caused by factors such as modified combustion efficiency (MCE), fuel type, and information related to aerosol chemical composition (e.g., presence of brown carbon (BrC), single-scatter albedo, absorption Ångström exponent).

To overcome these limitations and address the issue of uncertainty in EFBC, we hypothesize that systematic inter-comparisons of various techniques will enable the identification, quantification, and constraint of uncertainties associated with BC emissions from open biomass burning. This will be accomplished by deploying various BC instruments to the Fire Sciences Laboratory (FSL) in Missoula, MT as part of the NOAA FIREX campaign. This will include one in situ method for eBC, four filter-based methods for eBC, one method for rBC, and one method for EC. All will share a common sampling inlet, thus eliminating any systematic sampling biases across the approaches. We will conduct statistical analyses to quantify differences among the various instruments and explore associations between EFBC measurements and factors such as MCE, fuel type, and aerosol chemical composition to improve the understanding of EFBC uncertainties.

The key outcome from this research will be the reconciliation of uncertainties associated with EFBC. Our data analysis and interpretation will provide the means to identify and quantify uncertainties as well as derive conversion factors that can be applied to both historic and future BC datasets to constrain the uncertainties associated with EFBC in emission inventories. Ultimately, this research will facilitate the development of more robust emission inventories and hence, improved predictions by atmospheric chemical transport and climate models.