Exploring aerosol size distributions from polar to tropical zones of the Atlantic Ocean

Aerosols over the oceans significantly influence the composition of the Earth’s atmosphere and climate. Over the vast expanse of oceans, aerosols are emitted at high rates, primarily through wave breaking and bubble bursting. Additionally, secondary aerosol particles can be formed by gas-phase reactions. Particles emitted from shipping activities, long-range transport from continents, and potential downward transport from the upper troposphere can also contribute to aerosols in the marine boundary layer (MBL). Hence, marine aerosols represent a highly heterogeneous and complex mixture pivotal in regulating the global radiation budget.

This study explores aerosol number size distributions over the North Atlantic Ocean measured on the research vessel S/Y Eugen Seibold. The cruises conducted between June 2020 and September 2021 covered a broad geographic range from polar (~67° N) to tropical (~3° N) waters. Aerosols were sampled at approximately 13 m above the ocean surface using two sets of instrumentation covering particle sizes of 10 nm to 430 nm and 520 nm to 20 µm.

Three aerosol size modes, Aitken, accumulation, and coarse, were consistently identified throughout the dataset, aligning with prior research. Additionally, we observed an intermittently occurring nucleation mode and a bimodal coarse mode. While the presence of a nucleation mode suggests aerosol formation over the open ocean, it did not exhibit the typical banana-shaped contour plots usually observed during new particle formation and subsequent growth. Prior research indicates that ships may act as emitters in this size range, in addition to secondary formation from atmospheric gases.

Here, we describe and discuss particle number size distributions observed over the open ocean, raising questions about the formation and lifecycle of aerosol modes. Our goal is to track the behavior of nucleation, Aitken, accumulation and coarse modes in the MBL with high temporal resolution, spanning the latitudinal range of the northern Atlantic Ocean. A comprehensive dataset is prepared by incorporating surface ocean data retrieved on board and satellite observations to disentangle the natural and/or anthropogenic origins of aerosols responsible for the observed particle number size distributions in the MBL.