24 May 2022
24 May 2022
Status: this preprint is currently under review for the journal ACP.

African Smoke Particles Act as Cloud Condensation Nuclei in the Wintertime Tropical North Atlantic Boundary Layer over Barbados

Haley M. Royer1, Mira L. Pöhlker2,3,4, Ovid Krüger2, Edmund Blades5,6, Peter Sealy5, Nurun Nahar Lata7, Zezhen Cheng7, Swarup China7, Andrew P. Ault8, Patricia K. Quinn9, Paquita Zuidema1, Christopher Pöhlker2, Ulrich Pöschl2, and Cassandra Gaston1 Haley M. Royer et al.
  • 1Department of Atmospheric Sciences, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL
  • 2Department of Multiphase Chemistry, Max Planck Institute for Chemistry, Mainz, Germany
  • 3Leipzig Institute for Meteorology, Leipzig University, Leipzig, Germany
  • 4Experimental Aerosol and Cloud Microphysics Department, Leibniz Institute for Tropospheric Research, Leipzig, Germany
  • 5Barbados Atmospheric Chemistry Observatory, Ragged Point, Barbados
  • 6Queen Elizabeth Hospital Barbados, Bridgetown, Barbados
  • 7Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA
  • 8Department of Chemistry, University of Michigan, Ann Arbor, MI
  • 9Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle, WA

Abstract. The number concentration and properties of aerosol particles serving as cloud condensation nuclei (CCN) are important for understanding cloud formation, particularly in the tropical Atlantic marine boundary layer (MBL) where marine cumulus clouds reflect incoming solar radiation and obscure the low-albedo ocean surface. Studies linking aerosol source, composition, and water uptake properties in this region have been conducted primarily during summertime dust transport, despite the region receiving a variety of aerosol particle types throughout the year. In this study, we compare size-resolved aerosol chemical composition data to the hygroscopicity parameter κ derived from size-resolved CCN measurements made during the EUREC4A and ATOMIC campaigns from January to February 2020. We observed unexpected periods of wintertime long-range transport of African smoke and dust to Barbados. During these periods, the accumulation mode aerosol particle and CCN number concentrations as well as the proportions of dust and smoke particles increased while the average κ slightly decreased (κ = 0.45+0.1) from marine background conditions (κ = 0.52+0.08) when the particles were mostly composed of marine organics and sulfate. Size-resolved chemical analysis shows that smoke particles were the major contributor to the accumulation mode aerosol during long-range transport events, indicating that smoke is mainly responsible for the observed increase in CCN number concentrations. Earlier studies conducted at Barbados have mostly focused on the role of dust on CCN, but our results show that aerosol hygroscopicity and CCN number concentrations during wintertime long-range transport events over the tropical North Atlantic are affected by African smoke more than dust. Our findings highlight the importance of African smoke for atmospheric processes and cloud formation over the Caribbean.

Haley M. Royer et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-341', Anonymous Referee #1, 15 Jun 2022
  • RC2: 'Comment on acp-2022-341', Anonymous Referee #2, 26 Aug 2022

Haley M. Royer et al.

Haley M. Royer et al.


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Short summary
This paper presents atmospheric particle chemical composition and measurements of aerosol water uptake properties collected at Ragged Point, Barbados during the winter of 2020. The result of this study indicates the importance of small African smoke particles on cloud droplet formation in the tropical North Atlantic and highlights the large spatial and temporal pervasiveness of smoke over the Atlantic Ocean.