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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  07 Aug 2020

07 Aug 2020

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This preprint is currently under review for the journal ACP.

Factors controlling marine aerosol size distributions and their climate effects over the Northwest Atlantic Ocean region

Betty Croft1, Randall V. Martin2,1, Richard H. Moore3, Luke D. Ziemba3, Ewan C. Crosbie3,4, Hongyu Liu5, Lynn M. Russell6, Georges Saliba6, Armin Wisthaler7,8, Markus Müller7, Arne Schiller7, Martí Galí9, Rachel Y.-W. Chang1, Erin E. McDuffie1,2, Kelsey R. Bilsback10, and Jeffrey R. Pierce10 Betty Croft et al.
  • 1Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, Canada
  • 2McKelvey School of Engineering, Washington University in St. Louis, St. Louis, MO, USA
  • 3NASA Langley Research Center, Hampton, VA, USA
  • 4Science Systems and Applications, Inc., Hampton, VA, USA
  • 5National Institute of Aerospace, Hampton, VA, USA
  • 6Scripps Institute of Oceanography, University of California, San Diego, La Jolla, CA, USA
  • 7Institute for Ion Physics and Applied Physics, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
  • 8Department of Chemistry, University of Oslo, P.O. 1033 – Blindern, 0315 Oslo, Norway
  • 9Barcelona Supercomputing Center (BSC)
  • 10Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA

Abstract. Aerosols over Earth's remote and spatially extensive ocean surfaces have important influences on planetary climate. However, these aerosols and their effects remain poorly understood, in part due to the remoteness and limited observations over these regions. In this study, we seek to understand factors that shape marine aerosol size distributions and composition in the Northwest Atlantic Ocean region. We use the GEOS-Chem-TOMAS model to interpret measurements collected from ship and aircraft during the four seasonal campaigns of the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) conducted between 2015 and 2018. Observations from the NAAMES campaigns show enhancements in aerosol total number concentration at atmospheric altitudes of about 1 km, most pronounced during the phytoplankton bloom maxima (May/June). Our simulations, combined with NAAMES ship and aircraft measurements, suggest several key factors contribute to aerosol number and size in the Northwest Atlantic lower troposphere, with significant regional-mean (40–60° N, 20–50° W) aerosol-cloud albedo indirect effects (AIE) and direct radiative effects (DRE) during the phytoplankton bloom. These key factors and their associated radiative effects in the region are: (1) particle formation above/near the marine boundary layer (MBL) top (AIE: −3.37 W m−2, DRE: −0.62 W m−2), (2) particle growth due to marine secondary organic aerosol (MSOA) as the nascent particles subside into the MBL, enabling them to become cloud-condensation-nuclei-size particles (AIE: −2.27 W m−2, DRE: −0.10 W m−2), (3) particle formation/growth due to the products of dimethyl sulfide, above/within the MBL (−1.29 W m−2, DRE: −0.06 W m−2), and (4) ship emissions (AIE: −0.62 W m−2, DRE: −0.05 W m−2). Our results suggest a synergy of particle formation near the MBL top and growth by MSOA that contributes strongly to cloud-condensation-nuclei-sized particles with significant regional radiative effects in the Northwest Atlantic. Future work is needed to understand the sources and temperature-dependence of condensable marine vapors forming MSOA and to understand the species that can form new particles at the boundary layer top and grow these particles as they descend into the marine boundary layer.

Betty Croft et al.

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Betty Croft et al.

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Publications Copernicus
Short summary
Atmospheric particles over Earth's ocean surfaces have important climate effects. We examine key factors contributing to particle number, size and radiative effects over the Northwest Atlantic Ocean. Our results suggest key contributors are (1) particle formation near the marine boundary layer top, (2) particle growth by marine secondary organic aerosol, (3) dimethyl sulfide oxidation products and (4) ship emissions. We interpret NAAMES ship and aircraft measurements with the GEOS-Chem-TOMAS model.
Atmospheric particles over Earth's ocean surfaces have important climate effects. We examine key...