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The Ascension Island Boundary Layer in the Remote Southeast Atlantic is Often Smoky

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 condensa...

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Published in:Geophysical research letters 2018-05, Vol.45 (9), p.4456-4465
Main Authors: Zuidema, Paquita, Sedlacek, Arthur J., Flynn, Connor, Springston, Stephen, Delgadillo, Rodrigo, Zhang, Jianhao, Aiken, Allison C., Koontz, Annette, Muradyan, Paytsar
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cited_by cdi_FETCH-LOGICAL-c3716-bec313d328b3f35a113d9f790dbf70ec4775f67c419e16402cda6c2c5768e8aa3
cites cdi_FETCH-LOGICAL-c3716-bec313d328b3f35a113d9f790dbf70ec4775f67c419e16402cda6c2c5768e8aa3
container_end_page 4465
container_issue 9
container_start_page 4456
container_title Geophysical research letters
container_volume 45
creator Zuidema, Paquita
Sedlacek, Arthur J.
Flynn, Connor
Springston, Stephen
Delgadillo, Rodrigo
Zhang, Jianhao
Aiken, Allison C.
Koontz, Annette
Muradyan, Paytsar
description 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. Plain Language Summary First findings from the remote Ascension Island midway between Africa and South America in the Atlantic Ocean indicate that smoke is present much more often near the surface than has been previously thought. The new measurements from a 17‐month‐long campaign suggest that August is the smokiest month near the surface. The smoke includes other aerosols besides black carbon, and is most absorptive of sunlight in June and least in October. The smoke is more present near the surface earlier in the biomass burning season, or June, while later on toward September and October, more of the smoke resides above the cloud layer. This has implications for which aerosol‐cloud microphysical and radiative interactions are dominant when. The campaign‐maximum aerosol loading event is investigated further and attributed to an unusual direct westward flow from the continental African fire sources at low altitudes. Key Points Refractory black carbon is often
doi_str_mv 10.1002/2017GL076926
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(BNL), Upton, NY (United States) ; Los Alamos National Lab. (LANL), Los Alamos, NM (United States) ; Argonne National Lab. (ANL), Argonne, IL (United States) ; Univ. of Miami, FL (United States) ; Pacific Northwest National Lab. (PNNL), Richland, WA (United States)</creatorcontrib><description>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. Plain Language Summary First findings from the remote Ascension Island midway between Africa and South America in the Atlantic Ocean indicate that smoke is present much more often near the surface than has been previously thought. The new measurements from a 17‐month‐long campaign suggest that August is the smokiest month near the surface. The smoke includes other aerosols besides black carbon, and is most absorptive of sunlight in June and least in October. The smoke is more present near the surface earlier in the biomass burning season, or June, while later on toward September and October, more of the smoke resides above the cloud layer. This has implications for which aerosol‐cloud microphysical and radiative interactions are dominant when. The campaign‐maximum aerosol loading event is investigated further and attributed to an unusual direct westward flow from the continental African fire sources at low altitudes. Key Points Refractory black carbon is often present in the remote marine boundary layer of the southeast most significantly from June to August A spectrally flat absorption angstrom exponent suggests that most light absorption is from lens‐coated black carbon The single‐scattering albedo increases from an August mean of 0.78 to 0.81 in September and 0.83 in October</description><identifier>ISSN: 0094-8276</identifier><identifier>EISSN: 1944-8007</identifier><identifier>DOI: 10.1002/2017GL076926</identifier><language>eng</language><publisher>Washington: John Wiley &amp; Sons, Inc</publisher><subject>absorbing aerosol ; Absorption ; Absorption coefficient ; Absorptivity ; Aerosol optical depth ; aerosol, atmospheric radiation, absorbing aerosols, field measurements, Aerosol optical Depth, absorption angstrom exponent ; Aerosols ; Albedo ; Albedo (solar) ; Biomass ; Biomass burning ; Black carbon ; Boundary layer ; Boundary layers ; Burning ; Carbon ; Cloud condensation nuclei ; Cloud condensation nuclei concentrations ; Cloud microphysics ; Clouds ; Coefficients ; Condensation ; Condensation nuclei ; Deployment ; DOE AMF1 ; Earth Sciences ; Electromagnetic absorption ; ENVIRONMENTAL SCIENCES ; Fires ; GEOSCIENCES ; Interactions ; Light absorption ; Low altitude ; Nuclei ; Nucleus ; Optical analysis ; OTHER INSTRUMENTATION ; remote southeast Atlantic ; Smoke ; Surface chemistry ; Wavelength ; Wavelengths</subject><ispartof>Geophysical research letters, 2018-05, Vol.45 (9), p.4456-4465</ispartof><rights>2018. 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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. Plain Language Summary First findings from the remote Ascension Island midway between Africa and South America in the Atlantic Ocean indicate that smoke is present much more often near the surface than has been previously thought. The new measurements from a 17‐month‐long campaign suggest that August is the smokiest month near the surface. The smoke includes other aerosols besides black carbon, and is most absorptive of sunlight in June and least in October. The smoke is more present near the surface earlier in the biomass burning season, or June, while later on toward September and October, more of the smoke resides above the cloud layer. This has implications for which aerosol‐cloud microphysical and radiative interactions are dominant when. The campaign‐maximum aerosol loading event is investigated further and attributed to an unusual direct westward flow from the continental African fire sources at low altitudes. 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(BNL), Upton, NY (United States)</aucorp><aucorp>Los Alamos National Lab. (LANL), Los Alamos, NM (United States)</aucorp><aucorp>Argonne National Lab. (ANL), Argonne, IL (United States)</aucorp><aucorp>Univ. of Miami, FL (United States)</aucorp><aucorp>Pacific Northwest National Lab. (PNNL), Richland, WA (United States)</aucorp><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>The Ascension Island Boundary Layer in the Remote Southeast Atlantic is Often Smoky</atitle><jtitle>Geophysical research letters</jtitle><date>2018-05-16</date><risdate>2018</risdate><volume>45</volume><issue>9</issue><spage>4456</spage><epage>4465</epage><pages>4456-4465</pages><issn>0094-8276</issn><eissn>1944-8007</eissn><abstract>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. Plain Language Summary First findings from the remote Ascension Island midway between Africa and South America in the Atlantic Ocean indicate that smoke is present much more often near the surface than has been previously thought. The new measurements from a 17‐month‐long campaign suggest that August is the smokiest month near the surface. The smoke includes other aerosols besides black carbon, and is most absorptive of sunlight in June and least in October. The smoke is more present near the surface earlier in the biomass burning season, or June, while later on toward September and October, more of the smoke resides above the cloud layer. This has implications for which aerosol‐cloud microphysical and radiative interactions are dominant when. The campaign‐maximum aerosol loading event is investigated further and attributed to an unusual direct westward flow from the continental African fire sources at low altitudes. Key Points Refractory black carbon is often present in the remote marine boundary layer of the southeast most significantly from June to August A spectrally flat absorption angstrom exponent suggests that most light absorption is from lens‐coated black carbon The single‐scattering albedo increases from an August mean of 0.78 to 0.81 in September and 0.83 in October</abstract><cop>Washington</cop><pub>John Wiley &amp; Sons, Inc</pub><doi>10.1002/2017GL076926</doi><tpages>10</tpages><orcidid>https://orcid.org/0000-0002-2799-2965</orcidid><orcidid>https://orcid.org/0000-0001-6988-2935</orcidid><orcidid>https://orcid.org/0000-0001-5749-7626</orcidid><orcidid>https://orcid.org/0000-0002-9182-6531</orcidid><orcidid>https://orcid.org/0000-0003-4719-372X</orcidid><orcidid>https://orcid.org/0000-0001-9595-3653</orcidid><orcidid>https://orcid.org/000000034719372X</orcidid><orcidid>https://orcid.org/0000000227992965</orcidid><orcidid>https://orcid.org/0000000169882935</orcidid><orcidid>https://orcid.org/0000000291826531</orcidid><orcidid>https://orcid.org/0000000195953653</orcidid><orcidid>https://orcid.org/0000000157497626</orcidid><oa>free_for_read</oa></addata></record>
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identifier ISSN: 0094-8276
ispartof Geophysical research letters, 2018-05, Vol.45 (9), p.4456-4465
issn 0094-8276
1944-8007
language eng
recordid cdi_osti_scitechconnect_1433942
source Wiley-Blackwell AGU Digital Archive
subjects absorbing aerosol
Absorption
Absorption coefficient
Absorptivity
Aerosol optical depth
aerosol, atmospheric radiation, absorbing aerosols, field measurements, Aerosol optical Depth, absorption angstrom exponent
Aerosols
Albedo
Albedo (solar)
Biomass
Biomass burning
Black carbon
Boundary layer
Boundary layers
Burning
Carbon
Cloud condensation nuclei
Cloud condensation nuclei concentrations
Cloud microphysics
Clouds
Coefficients
Condensation
Condensation nuclei
Deployment
DOE AMF1
Earth Sciences
Electromagnetic absorption
ENVIRONMENTAL SCIENCES
Fires
GEOSCIENCES
Interactions
Light absorption
Low altitude
Nuclei
Nucleus
Optical analysis
OTHER INSTRUMENTATION
remote southeast Atlantic
Smoke
Surface chemistry
Wavelength
Wavelengths
title The Ascension Island Boundary Layer in the Remote Southeast Atlantic is Often Smoky
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