04 Jul 2024
 | 04 Jul 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Quantifying the Impacts of Marine Aerosols over the Southeast Atlantic Ocean using a chemical transport model: Implications for aerosol-cloud interactions

Mashiat Hossain, Rebecca M. Garland, and Hannah M. Horowitz

Abstract. The southeast Atlantic region, characterized by persistent stratocumulus clouds, has one of the highest uncertainties in aerosol radiative forcing and significant variability across climate models. In this study, we analyze the seasonally varying role of marine aerosol sources and identify key uncertainties in aerosol composition at cloud-relevant altitudes over the southeast Atlantic using the GEOS-Chem chemical transport model. We evaluate simulated aerosol optical depth (AOD) and speciated aerosol concentrations against those collected from ground observations and aircraft campaigns such as LASIC, ORACLES, and CLARIFY, conducted during 2017. The model consistently underestimates AOD relative to AERONET, particularly at remote locations like Ascension Island. However, when compared with aerosol mass concentrations from aircraft campaigns during the biomass burning period, it performs adequately at cloud-relevant altitudes, with a normalized mean bias (NMB) between −3.5 % (CLARIFY) and −7.5 % (ORACLES). At these altitudes, organic aerosols (63 %) dominate during the biomass burning period, while sulfate (41 %) prevails during austral summer, when dimethylsulfide (DMS) emissions peak in the model. Our findings indicate that marine sulfate can account for up to 69 % of total sulfate during high DMS period. Sensitivity analyses indicate that refining DMS emissions and oxidation chemistry may increase sulfate aerosol produced from marine sources, highlighting their overall importance. Additionally, we find marine primary organic aerosol emissions may substantially increase total organic aerosol concentrations, particularly during austral summer. This study underscores the imperative need to refine marine emissions and their chemical transformations to better predict aerosol-cloud interactions and reduce uncertainties in aerosol radiative forcing over the southeast Atlantic.

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Mashiat Hossain, Rebecca M. Garland, and Hannah M. Horowitz

Status: open (until 21 Aug 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-1948', Anonymous Referee #1, 23 Jul 2024 reply
Mashiat Hossain, Rebecca M. Garland, and Hannah M. Horowitz
Mashiat Hossain, Rebecca M. Garland, and Hannah M. Horowitz


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Short summary
Our research examines aerosol dynamics over the southeast Atlantic, a region with significant uncertainties in aerosol radiative forcings. Using the GEOS-Chem model, we find that at cloud altitudes, organic aerosols dominate during the biomass burning season, while sulfate aerosols, driven by marine emissions, prevail during peak primary production. These findings highlight the need for accurate representation of marine aerosols in models to improve climate predictions and reduce uncertainties.