Space experiment could teach us how aerosols move in the atmosphere

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Jeffrey Moran

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As a child, Jeffrey Moran was fascinated by outer space. Now, he is designing an experiment to be carried out on the International Space Station (ISS) in 2025.

"I was obsessed with aerospace as a kid," said the mechanical engineering assistant professor at George Mason University. "The house I grew up in is still littered with model airplanes and drawings of Space Shuttles. Airplanes and spacecraft were a major reason I chose engineering when I got to college."

Jeffrey Moran. Photo by Office of University Branding

When the National Science Foundation issued a call for proposals to conduct research projects on the ISS to benefit life on earth, Moran jumped at the chance and wrote a proposal that was successfully funded. His grant-winning experiment will examine the extent to which certain aerosols (small particles suspended in air) move by thermophoresis, which is the scientific term for the motion of small particles in nonuniform temperatures.

"This project really started from a 'hey, what if we did this' conversation with my colleague," said Moran, describing the conversation he had with Purdue University colleague David Warsinger, during which the pair developed the idea of studying microswimmers (small, moving particles) suspended in air.

"My lab focuses on developing self-propelled particles for applications like water treatment or drug delivery," said Moran. "It's a new and exciting field, but it's so far been restricted entirely to water environments. No one has tried to develop a swimmer that moves in air. That ties into climate change, because aerosols are everywhere in the atmosphere-both because of human activity, like burning fossil fuels, and because of natural events like volcanic eruptions-and we don't have a solid understanding of the net effect aerosols will have on the climate."

Understanding how particles in air move due to temperatures around them could help scientists better understand and predict changes in the atmosphere not only due to the earth's movement relative to the position of the sun but also because of manmade influences on the environment. Doing the experiment in space allows scientists to run their tests with a minimal influence of gravity, to purely examine the effect of temperature on aerosols without creating air currents (such as those that occur in a convection oven).

"We're going to send various particles into space, each in a specially designed cuvette, for the astronauts to test," Moran explained. "There's a microscope on the ISS, and the astronauts will place our cuvettes into an apparatus we've designed that applies heat and cold to opposite ends of the cuvette. The astronauts will then measure how fast the particles move towards hot or towards cold."

For the last part of the project, Moran said they were going to see whether some particles with asymmetric properties might generate the propulsive temperature difference on their own. "These particles will have one side coated in a metal. The other side is an insulating material," Moran explained. "When we shine a light on them, the metal side absorbs light more efficiently and heats up relative to the insulating side. This has been observed on earth to lead to propulsion, but has never been tested in air, nor has it been observed in space."

Before the experiment can be carried out, Moran and his team need to determine the experiment's parameters as well as the materials required.

"This is very much a work in progress," said Moran. "We're figuring out exactly which particles we want to send to the space station [based on] which materials matter the most to climate scientists [and] what the biggest question marks are."

He mentioned, among other examples, the possibility of experimenting with carbon soot.

"Carbon soot is produced by burning fossil fuels, and it's known to be harmful to the environment because it absorbs sunlight efficiently," he said. "Another source of carbon soot, increasingly common in this era, is from rocket launches."

"It's pretty well established that carbon soot overall intensifies warming," he said. "It's black, so it tends to absorb sunlight efficiently. This leads to a net warming effect on the atmosphere, but it's not clear how much it moves in thermophoresis [how much it moves in temperature differences]."

Moran looks forward to working with the National Aeronautics and Space Administration (NASA) to refine the plan. An early step in this project will be for Moran and his team to travel to Texas to examine a replica of the equipment available to scientists on the International Space Station.

The College of Engineering and Computing will cover Moran's progress as the project moves forward.