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Title: The Ascension Island boundary layer in the remote southeast Atlantic is often smoky

Observations from June through 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. 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 indirectly indicate the presence of other light-absorbing aerosols (e.g., brown carbon), most pronounced in June. 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 of 2016, is investigated further. Also, backtrajectories indicate more direct boundary layer transport westward from the African continent is central to explaining the elevated surface aerosol loadings.
ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [3] ;  [2] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [4] ;  [3] ;  [5]
  1. Univ. of Miami, Miami, FL (United States). Rosenstiel School of Marine and Atmospheric Sciences
  2. Brookhaven National Lab. (BNL), Upton, NY (United States)
  3. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  4. Los Alamos National Laboratory, Los Alamos NM USA
  5. Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 0094-8276
Grant/Contract Number:
SC0012704; SC0013720
Accepted Manuscript
Journal Name:
Geophysical Research Letters
Additional Journal Information:
Journal Name: Geophysical Research Letters; Journal ID: ISSN 0094-8276
American Geophysical Union
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Scientific User Facilities Division; National Aeronautic and Space Administration (NASA)-Aerosol Robotic Network (AERONET)
Country of Publication:
United States
OSTI Identifier: