Award: OCE-2023110

Atmospheric aerosol particles are small solids or liquids suspended in the air. Most common examples are dust and smoke from forest fires. These aerosol particles are ubiquitous in the atmosphere and have important impacts on human health and the environment, including impacts on weather. Understanding the sources of the aerosol particles are important for understanding and predicting their properties and impacts on humans and the environment. In this study, we aim to understand the sources and physical properties of aerosol particles emitted directly from the ocean. It is important to understand the composition and properties of natural aerosol particles in order to have a baseline to understand any changes or inputs from human behavior.

Wind over the ocean causes breaking waves. When the waves crest, the falling water pulls air below the surface of the ocean. That air then forms bubbles which rise back up to the surface. As the bubbles rise, they can collect organics in the seawater, since they stick to the surface of the bubbles. When the bubbles reach the surface, they can accumulate there and eventually burst. The film of the bubble breaks up into tiny pieces, referred to as aerosol particles. These aerosol particles have a lot of organics, as well as some sea salt. The bubbles can also emit slightly larger particles that have compositions similar to seawater and are mostly sea salt and water. These particles can then be transported in the atmosphere and can change size and composition by interacting with humidity, gases, other particles, and sunlight.   

The number of particles emitted, and their physical and chemical properties, are dependent on the conditions of the seawater, such as the organic species in the seawater and the temperature of the water.

In this study, we used a custom-built ocean atmosphere model to mimic this bubble bursting process and isolate a few key factors to study the emitted particles. This system consists of a large, sealed, glass tank that holds 40 L of seawater. This was deployed on board the R/V Atlantic Explorer in a shipping container converted into a mobile lab van, equipped with instrumentation to measure the size and number of the aerosol particles. Seawater was continuously pumped into the model system. Bubbles were created by pumping seawater and ultrapure air through the Venturi nozzle. The bubbles then rose to the surface of the model ocean and burst. The particles were emitting into the model atmosphere and then pulled into the instrumentation or collected on filters for chemical analyses in the laboratory.

In this study, we generated and measured aerosol particles in summer 2021 and winter 2023 from seawater in the North Atlantic Ocean, at the Bermuda Atlantic Time Series station, near Bermuda. We found that the number of particles produced from ocean waves varied as a function of the season and resulting seawater properties. The production efficiency of particles was twice as high in the summer as in the winter. On average, the generated particles were slightly smaller in the summer compared to the winter. The lower temperature of the seawater in the winter may have changed the surface tension of the bubbles and the number of particles they emit. The concentrations of surface-active organics likely also contribute to the properties of both the bubbles and the particles produced. These seasonal differences indicate that particle production will also vary widely for different seawater types and depend largely on the seawater properties.

This work is described in a video on the Frossard Lab website. Additionally, discussions of these measurements are included when teaching courses focused on quantitative analytical chemistry as well as atmospheric chemistry.

 

Last Modified: 02/27/2026
Modified by: Amanda Ann Frossard