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The earth’s atmosphere is full of aerosols, both from natural events such as volcanic eruptions and human activity such as burning fossil fuels. The Department of Mechanical Engineering’s Jeffrey Moran is planning an experiment on the International Space Station (ISS) to better understand what factors drive aerosols from place to place, which could enable climate scientists to predict the overall effect of aerosols on climate with less uncertainty.
“Aerosols can exacerbate or alleviate climate change, depending on what they’re made of,” explained Moran. “For example, carbon soot aerosols can intensify warming by absorbing sunlight that would otherwise be reflected back into space. Other aerosols, such as sulfates, can reduce warming by increasing solar reflection.” Aerosols’ location also matters – for example, many aerosols can act as nuclei for clouds to form, and this can exert an overall warming or cooling effect in different locations. “The overall effect aerosols will have on the climate is hard to predict, partly because we don’t have a full understanding of what factors cause them to migrate from one place to another,” said Moran.
The experiment is specifically examining whether and how temperature gradients influence the movement of certain aerosols through the atmosphere. Moran’s team, along with his collaborator, Assistant Professor David Warsinger of Purdue University, and a team of undergraduate students there, are designing an apparatus inside of which aerosols of a certain size can be observed across a temperature gradient. They recently completed a fit check to confirm that the apparatus both fits in the ISS microscope’s enclosure and that the aerosol container, or cuvette, is transparent enough for observation.
Moran said the experiment could help climate researchers understand how temperature differences, which are common in the atmosphere, cause particles to move through the air.
“If the effect of the temperature gradient is significant, it could give us a clearer indication of how aerosols will affect the climate in the future. It could also inform geoengineering proposals, which would seek to mitigate climate change by intentionally injecting aerosols into the atmosphere, since we would have a better sense of where they will go, and thus what their overall effect will be,” said Moran. “It could also offer a way to control aerosols on the ground, for example, by using thermophoresis to collect virus-laden aerosols from the HVAC systems of hospitals.”
The team’s apparatus includes a 3D-printed stage with hot and cold fixtures on either end. A prototype cuvette is mounted between them in the enclosure of the microscope. Crucially, the apparatus fits snugly inside the microscope enclosure, which is necessary for the experiment to be carried out in microgravity.
“The capstone team did a wonderful job,” Moran added. The team tested the cuvette’s transparency by placing sodium chloride, table salt, inside it and taking images with the microscope. To verify airtightness, the team placed the salt-filled cuvette in a beaker of water and observed that the salt (which is soluble in water) remained in its solid form, indicating no water had leaked into the cuvette. “We obviously don’t want to pose an inhalation hazard to the ISS crew, so it’s important that the particle samples be packaged on the ground in containers that are as close to airtight as possible,” said Moran.
“These images are a promising first step, as they demonstrate that aerosols in the range of sizes we are considering (10-100 µm) can be clearly imaged through the prototype cuvettes using a microscope nearly identical to the one currently on the ISS,” said Moran.
From here, Moran, Warsinger, and a new team of students will work to improve the cuvette fabrication and polishing procedures. They will also test alternative cuvette materials such as quartz, which may be thinner and more transparent, thereby allowing them to take clearer images at a higher magnification. This would enable them to examine even smaller aerosol particles. The team is also refining the design of the cuvettes to improve optical transparency and minimize the thickness of the windows. “We want to make the cuvettes smaller, bringing the hot and cold surfaces as close together as we can get them, because it's not really clear how steep of a temperature gradient we're going to need to induce motion,” Moran explained.
In addition, the team is finalizing their choice of aerosol materials to send to the ISS. They are currently set on using carbon soot, sodium chloride, and silica due to their relevance in atmospheric aerosols and climate science.
“Carbon soot is one of the most important materials in terms of climate, because it is known to intensify warming,” Moran said, adding that sodium chloride enters the atmosphere as sea spray and can drift to faraway locations, such as the North Pole, intensifying the warming that is already happening at a rapid pace there. Silica is a common ingredient in sand and thus a common material in the atmosphere as well. Overall, the team aims to strike a balance between having materials that can be studied safely on the ISS while also yielding insights into aerosol dynamics in the atmosphere.
The College of Engineering and Computing will cover Moran’s progress leading up to the experiment in space, scheduled for fall 2025 or spring 2026.