An Evaluation of Biomass Burning Aerosol Mass, Extinction, and Size Distribution in GEOS using Observations from CAMP2Ex
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Date
2022-08-29
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Citation of Original Publication
Collow, A. B. M., Buchard, V., Colarco, P. R., da Silva, A. M., Govindaraju, R., Nowottnick, E. P., Burton, S., Ferrare, R., Hostetler, C., and Ziemba, L.: An Evaluation of Biomass Burning Aerosol Mass, Extinction, and Size Distribution in GEOS using Observations from CAMP2Ex, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2022-545, in review, 2022.
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract
Biomass burning aerosol impacts aspects of the atmosphere and Earth system through radiative forcing, serving as
cloud condensation nuclei, and air quality. Despite its importance, the representation of biomass burning aerosol is not always
15 accurate in numerical weather prediction and climate models or reanalysis products. Using observations collected as part of
the Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) in August through October of 2019, aerosol
concentration and optical properties are evaluated within the Goddard Earth Observing System (GEOS) and its underlying
aerosol module, GOCART. In the operational configuration, GEOS assimilates aerosol optical depth observations at 550 nm
to constrain aerosol fields. Particularly for biomass burning aerosol, without the assimilation of aerosol optical depth, aerosol
extinction is underestimated compared to observations collected in the Philippines region during the CAMP2 20 Ex campaign. The
assimilation process adds excessive amounts of carbon to account for the underestimated extinction, resulting in positive biases
in the mass of black and organic carbon, especially within the boundary layer, relative to in situ observations from the Langley
Aerosol Research Group Experiment. Counteracting this, GEOS is deficient in sulphate and nitrate aerosol just above the
boundary layer. Aside from aerosol mass, extinction within GEOS is a function of ambient relative humidity and an assumed
25 particle size distribution. The relationship between dry and ambient extinction in GEOS reveals that hygroscopic growth is too
aggressive within the model for biomass burning aerosol. An additional concern lies in the assumed particle size distribution
for GEOS, which has a mode radius that is too small for organic carbon. Variability in the observed particle size distribution
for biomass burning aerosol within a single flight also illuminates the fact that a single assumed particle size distribution is not
sufficient and that for a proper representation, a more advanced aerosol module with GEOS may be necessary.