Researchers Characterize Sea Spray Particles That Form Ice Crystals in High-Altitude Clouds

Published: 17 January 2023

NSF- and ASR-funded research allows for particle and freezing analyses that enhance the understanding of cloud formation and effects on climate

The following is based on a story by Stony Brook University.

Wearing safety glasses and surrounded by tubing, Daniel Knopf and Josephine Aller work together in a lab.
Daniel Knopf and Josephine Aller work in the School of Marine and Atmospheric Sciences Aerosol Research Laboratory at Stony Brook University, where they simulate aerosols from ocean waters that can initiate ice crystals affecting cloud formation. Photo is by John Griffin, Stony Brook University.

While there are several sources of ice-forming particles in the atmosphere, sea spray aerosols (SSAs) are recognized as a significant source of ice-nucleating particles (INPs). But what SSAs are composed of, how they affect cloud formation, and how they may affect climate remains an important question for atmospheric scientists.

Now researchers at Stony Brook University have developed a way to simulate SSAs in laboratory tanks that mirror ocean conditions. This has allowed them to determine the organic compounds associated with and released by growing marine microorganisms and discover clues to the role of these compounds as INPs.

The team also studied ice formation, a complex process driven by various mechanisms. These new results, in combination with previous studies, allowed for the development of a holistic SSA-INP freezing parameterization for implementation in cloud-resolving and climate models. Their findings are detailed in a paper published in Science Advances.

The work—led by Stony Brook atmospheric chemists Peter Alpert (now at Paul Scherrer Institute Switzerland), atmospheric scientist Daniel Knopf, and microbial oceanographer Josephine Aller—was supported by the U.S. Department of Energy’s (DOE) Atmospheric System Research (ASR) program through an ASR project and a previous National Science Foundation (NSF) grant to Aller that allowed them to initiate this research.

This study’s freezing parameterization development, crucial to improving atmospheric models, drew upon data collected by DOE’s Atmospheric Radiation Measurement (ARM) user facility. ARM field campaigns and related papers that were useful to this study included:

Aerosols generated by bubbles and winds blowing over the ocean surface form sprays of fine salt particles coated with organic compounds that can be transported high up into the atmosphere, where clouds form. They are among various other particle types, including dust, soot, and ash from wildfires, that contribute to ice formation in the atmosphere.

Oceans cover 70 percent of the planet, with areas away from the continents where SSAs are the significant contributors to INPs and cloud formation. For scientists to predict the formation of clouds and to assess their climatic impact, they first need to understand under which conditions ice crystals can form from particles originating from the ocean, which is the largest source of INPs.

The Stony Brook research team simulated ocean water and generated ice-forming SSA particles. They examined these and found that the SSA particles were made up of the metabolic products of microorganisms living near the ocean surface.

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ARM is a DOE Office of Science user facility operated by nine DOE national laboratories.