Sea spray losing its sparkle?

July 3, 2017, Stockholm University
Credit: CC0 Public Domain

Atmospheric aerosols are tiny particles that scatter and absorb sunlight but also influence climate indirectly through their role in cloud formation. One of the largest sources of aerosols is sea spray which is produced over the world's oceans. Understanding how these particles take up water from the atmosphere, their so-called hygroscopicity, is important because it determines how much sunlight they reflect and how well they can form clouds. This was the topic of a new study by researchers from Stockholm University and international partners published in Nature Communications.

"It is widely understood that aerosols have a net cooling effect on climate, counteracting the warming caused by greenhouse gases. However, the magnitude of this cooling is highly uncertain, in part due to knowledge gaps in how natural aerosol interact with solar radiation and clouds," says Matt Salter, researcher at the Department of Environmental Science and Analytical Chemistry (ACES), Stockholm University, and co-author of the study.

Sea spray is a complex mixture of inorganic salts, organic material present in the ocean and living organisms such as bacteria, viruses and fungi. The ability of the inorganic component of particles to take up has been the focus of this international study where a large suite of well-controlled laboratory experiments have shown, for the first time, that the hygroscopicity of the inorganic component of sea spray is significantly lower than pure sodium chloride, a substance routinely used to describe their hygroscopicity in climate models.

"All numerical models are simplified reflections of reality which require approximations. It was previously thought that sodium chloride was a good approximation for the hygroscopicity of the inorganic fraction of sea spray. We have now shown that the hygroscopicity of pure inorganic sea spray particles is significantly lower than . This finding has implications for the role of sea spray aerosols in climate, especially on how they interact with , " says Paul Zieger, assistant professor at ACES and co-author of the study.

Using models, the authors were able to show that the reduced hygroscopicity of sea spray means that these particles will grow less and reflect less sunlight than previously thought. However, the picture may be more complicated.

"We suspect that water bound within sea salt, known as hydrates, play a significant role in defining the hygroscopicity of inorganic sea aerosol, If true, it means that the particles would take up less water because of the water already present as hydrates and, as a result, they would grow less. Overall, improving our understanding of one of the largest natural sources is critical if we are to understand the effects of man-made aerosols on climate, " says Matt Salter.

Explore further: How plankton and bacteria shape ocean spray

More information: "Revising the hygroscopicity of inorganic sea salt particles"Nature Communications (2017). DOI: 10.1038/ncomms15883

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UKCatFan
not rated yet Jul 05, 2017
Reading between the lines, if the natural aerosols are reflecting significantly less light doesn't that mean any climate models that had that incorporated on historical data are off? It sounds like it would mean that they overstated the cooling effect of sea spray. To get the model to match historical patterns that should also mean they either overstated the warming effect of something else or underestimated the cooling effect of something else.

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