TY - JOUR
T1 - The Ascension Island Boundary Layer in the Remote Southeast Atlantic is Often Smoky
AU - Zuidema, Paquita
AU - Sedlacek, Arthur J.
AU - Flynn, Connor
AU - Springston, Stephen
AU - Delgadillo, Rodrigo
AU - Zhang, Jianhao
AU - Aiken, Allison C.
AU - Koontz, Annette
AU - Muradyan, Paytsar
N1 - Funding Information:
P. Z., R. D. and J. Z. gratefully acknowledge support from the Department of Energy (DOE) Atmospheric System Research (ASR) LASIC planning grant DE-SC0013720. Support is acknowledged from the DOE Office of Biological and Environmental Sciences (OBER) under contract DE-SC0012704 to AJS through the ASR program and to SS and ACK through the ASR and ARM programs. Connor Flynn was supported as Aerosol Lifecycle Working Group Translator by the OBER of the U.S. DOE as part of the ARM Climate Research Facility and Office of Science Scientific User Facility. Paytsar Muradyan is supported by the ARM Climate Research Facility. We thank Brent Holben and the AERONET team for their effort in establishing and maintaining the AERONET Ascension Island sites. Sarah Doherty helped us further articulate the meaning of a mass absorption coefficient, and Sharon Burton and Richard Ferrare helped us understand the lidar depolarization ratios. We thank Adeyemi Adebiyi for Figure 5f. We thank two anonymous reviewers for their thoughtful commentary. Acknowledgments to the individual data sets are provided in the Supplementary Information.
Publisher Copyright:
©2018. American Geophysical Union. All Rights Reserved.
PY - 2018/5/16
Y1 - 2018/5/16
N2 - Observations from June to October 2016, from a surface-based ARM Mobile Facility deployment on Ascension Island (8°S, 14.5°W) indicate that refractory black carbon (rBC) is almost always present within the boundary layer. The rBC mass concentrations, light absorption coefficients, and cloud condensation nuclei concentrations vary in concert and synoptically, peaking in August. Light absorption coefficients at three visible wavelengths as a function of rBC mass are approximately double that calculated from black carbon in lab studies. A spectrally-flat absorption angstrom exponent suggests most of the light absorption is from lens-coated black carbon. The single-scattering-albedo increases systematically from August to October in both 2016 and 2017, with monthly means of 0.78 ± 0.02 (August), 0.81 ± 0.03 (September), and 0.83 ± 0.03 (October) at the green wavelength. Boundary layer aerosol loadings are only loosely correlated with total aerosol optical depth, with smoke more likely to be present in the boundary layer earlier in the biomass burning season, evolving to smoke predominantly present above the cloud layers in September–October, typically resting upon the cloud top inversion. The time period with the campaign-maximum near-surface light absorption and column aerosol optical depth, on 13–16 August 2016, is investigated further. Backtrajectories that indicate more direct boundary layer transport westward from the African continent is central to explaining the elevated surface aerosol loadings.
AB - Observations from June to October 2016, from a surface-based ARM Mobile Facility deployment on Ascension Island (8°S, 14.5°W) indicate that refractory black carbon (rBC) is almost always present within the boundary layer. The rBC mass concentrations, light absorption coefficients, and cloud condensation nuclei concentrations vary in concert and synoptically, peaking in August. Light absorption coefficients at three visible wavelengths as a function of rBC mass are approximately double that calculated from black carbon in lab studies. A spectrally-flat absorption angstrom exponent suggests most of the light absorption is from lens-coated black carbon. The single-scattering-albedo increases systematically from August to October in both 2016 and 2017, with monthly means of 0.78 ± 0.02 (August), 0.81 ± 0.03 (September), and 0.83 ± 0.03 (October) at the green wavelength. Boundary layer aerosol loadings are only loosely correlated with total aerosol optical depth, with smoke more likely to be present in the boundary layer earlier in the biomass burning season, evolving to smoke predominantly present above the cloud layers in September–October, typically resting upon the cloud top inversion. The time period with the campaign-maximum near-surface light absorption and column aerosol optical depth, on 13–16 August 2016, is investigated further. Backtrajectories that indicate more direct boundary layer transport westward from the African continent is central to explaining the elevated surface aerosol loadings.
KW - DOE AMF1
KW - absorbing aerosol
KW - remote southeast Atlantic
KW - smoke
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U2 - 10.1002/2017GL076926
DO - 10.1002/2017GL076926
M3 - Article
AN - SCOPUS:85046803744
VL - 45
SP - 4456
EP - 4465
JO - Geophysical Research Letters
JF - Geophysical Research Letters
SN - 0094-8276
IS - 9
ER -