Blowing snow contributes to Arctic warming

When it comes to global warming trends, the Arctic is a troubling outlier. The Arctic warms nearly four times faster than the global average, and aerosols play an important role in that warming. Scientists have long known that pollutants from other regions can accumulate in the Arctic atmosphere where they alter atmospheric chemistry, absorb sunlight, and affect local weather patterns, leading to localized warming that melts ice and snow. Sea salt particles dominate aerosol mass concentration, but their production mechanisms and impact on Arctic climate have remained unclear.

Atmospheric scientists led by Jian Wang, director of the Center for Aerosol Science and Engineering (CASE) and professor of energy, environmental & chemical engineering in the McKelvey School of Engineering at Washington University in St. Louis, investigated the production and impact of sea salt aerosols on Arctic warming. Their results, published Sept. 4 in Nature Geoscience, revealed abundant fine sea salt aerosol production from blowing snow in the central Arctic, increasing particle concentration and cloud formation.

"Over the past few decades, scientists have identified 'Arctic haze' as the primary source of aerosols in the Arctic during winter and spring. This haze results from the long-range transport of pollutants," said Xianda Gong, first author on the study and a former postdoctoral researcher in Wang's lab. "However, our study reveals that local blowing snow, which produces sea salt particles, contributes a more substantial fraction to the total aerosol population in the central Arctic."

Wang's team analyzed data collected by the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC). Such observations are difficult to obtain -- the MOSAiC expedition entailed international collaboration and freezing an icebreaker into the central Arctic ice pack to drift with the sea ice for an entire year -- but essential to understanding the full picture of atmospheric conditions in the Arctic.

"The MOSAiC expedition let us observe how aerosols and clouds evolve over the course of a year and led to this discovery," Wang said. "Sea salt particles in the Arctic atmosphere aren't surprising, since there are ocean waves breaking that will generate sea salt aerosols. But we expect those particles from the ocean to be pretty large and not very abundant. We found sea salt particles that were much smaller and in higher concentration than expected when there was blowing snow under strong wind conditions," Wang said.

In the central Arctic, the coldest winter nights are the clearest, when heat from Earth can escape into space unimpeded. Under a cozy blanket of clouds, though, longwave radiation gets trapped and contributes to warming, so any process that leads to increased cloud formation and lingering cloudiness also boosts surface temperatures. Small aerosol particles, including those fine sea salt aerosols produced by blowing snow that Wang's team discovered, turn out to be very good for cloud formation.

"These sea salt particles can act as cloud condensation nuclei, leading to cloud formation," Gong said. "Considering the absence of sunlight in the winter and spring Arctic, these clouds have the capacity to trap surface long-wave radiation, thereby significantly warming the Arctic surface."

Though scientists had not observed this phenomenon before, fine sea salt aerosols from blowing snow have always been part of the Arctic climate system. With this observational confirmation and systematic study, which revealed that sea salt particles produced from blowing snow account for about 30% of total aerosol particles, climate models can now be updated to include the effects of these fine particles.

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Drops of seawater contain traces of an ancient world

Sea salt hides a secret: tiny droplets of the seawater from which it came, preserving geologic history.

Using specializing equipment obtained from National Science Foundation grant funds, Mebrahtu Weldeghebriel, PhD '22, a postdoctoral fellow at Princeton University, and Binghamton University Distinguished Professor of Earth Sciences Tim Lowenstein were able to reconstruct changes in seawater chemistry over the last 150 million years, also gaining insight into related geological processes and climate changes. Their article, "Seafloor Hydrothermal Systems Control Long-Term Changes in Seawater [Li+]: Evidence from Fluid Inclusions," was recently published in the journal Science Advances.

The ocean "is like a giant soup of different elements," Lowenstein explained. "Sodium and chloride are the most common ones, but there are dozens of others dissolved in seawater in trace amounts such as lithium."

They looked at sea salt (halite) formed at various times over the past 150 million years in geographically diverse sedimentary basins in the United States, Europe, Asia and Africa. Within the salt samples were tiny pockets containing a bit of ancient seawater.

To access the tiny droplets, the researchers used a laser to drill holes into the salt crystals and then a mass spectrometer to analyze the different trace elements present. In this research, they focused specifically on the concentration of lithium, a trace element that sustained a seven-fold decrease over the past 150 million years, paralleled by a rise in magnesium to calcium ratios.

But why?

The cause for the long-term variations in seawater composition has been debated for the past two decades. The researchers proposed that the decline in lithium concentration in seawater is mainly associated with reduced production of oceanic crust and decreased seafloor hydrothermal activity, both of which are influenced by the movements of tectonic plates. The slowdown in plate activity over the past 150 million years led to less lithium being added to the ocean and reduced amounts of carbon dioxide released into the atmosphere, which ultimately led to global cooling and the present ice age. Turning back the clock 150 million years, the earth was a warmer place with more carbon dioxide in the atmosphere and more lithium in the sea.

"There is a close link between ocean chemistry and atmospheric chemistry," Weldeghebriel said. "Whatever changes happen in the ocean also reflect what's happening in the atmosphere."

Overall, Weldeghebriel and Lowenstein's research has made a significant advance in understanding the chemistry of Earth's ancient oceans and how the movement of tectonic plates has influenced the composition of our Earth's hydrosphere and atmosphere. Such chemical changes impact biology, as well, such as the marine creatures that build their shells out of calcium carbonate.

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Researchers invent self-charging, ultra-thin device that generates electricity from air moisture

Imagine being able to generate electricity by harnessing moisture in the air around you with just everyday items like sea salt and a piece of fabric, or even powering everyday electronics with a non-toxic battery that is as thin as paper. A team of researchers from the National University of Singapore's (NUS) College of Design and Engineering (CDE) has developed a new moisture-driven electricity generation (MEG) device made of a thin layer of fabric -- about 0.3 millimetres (mm) in thickness -- sea salt, carbon ink, and a special water-absorbing gel.

The concept of MEG devices is built upon the ability of different materials to generate electricity from the interaction with moisture in the air. This area has been receiving growing interest due to its potential for a wide range of real-world applications, including self-powered devices such as wearable electronics like health monitors, electronic skin sensors, and information storage devices.

Key challenges of current MEG technologies include water saturation of the device when exposed to ambient humidity and unsatisfactory electrical performance. Thus, the electricity generated by conventional MEG devices is insufficient to power electrical devices and is also not sustainable.

To overcome these challenges, a research team led by Assistant Professor Tan Swee Ching from the Department of Materials Science and Engineering under CDE devised a novel MEG device containing two regions of different properties to perpetually maintain a difference in water content across the regions to generate electricity and allow for electrical output for hundreds of hours.

This technological breakthrough was published in the print version of scientific journal Advanced Materials on 26 May 2022.

Long-lasting, self-charging fabric-based 'battery'

The NUS team's MEG device consists of a thin layer of fabric which was coated with carbon nanoparticles. In their study, the team used a commercially available fabric made of wood pulp and polyester.

One region of the fabric is coated with a hygroscopic ionic hydrogel, and this region is known as the wet region. Made using sea salt, the special water-absorbing gel can absorb more than six times its original weight, and it is used to harvest moisture from the air.

"Sea salt was chosen as the water-absorbing compound due to its non-toxic properties and its potential to provide a sustainable option for desalination plants to dispose of the generated sea salt and brine," shared Asst Prof Tan.

The other end of the fabric is the dry region which does not contain a hygroscopic ionic hydrogel layer. This is to ensure that this region is kept dry and water is confined to the wet region.

Once the MEG device is assembled, electricity is generated when the ions of sea salt are separated as water is absorbed in the wet region. Free ions with a positive charge (cations) are absorbed by the carbon nanoparticles which are negatively charged. This causes changes to the surface of the fabric, generating an electric field across it. These changes to the surface also give the fabric the ability to store electricity for use later.

Using a unique design of wet-dry regions, NUS researchers were able to maintain high water content in the wet region and low water content in the dry region. This will sustain electrical output even when the wet region is saturated with water. After being left in an open humid environment for 30 days, water was still maintained in the wet region demonstrating the effectiveness of the device in sustaining electrical output.

"With this unique asymmetric structure, the electric performance of our MEG device is significantly improved in comparison with prior MEG technologies, thus making it possible to power many common electronic devices, such as health monitors and wearable electronics," explained Asst Prof Tan.

The team's MEG device also demonstrated high flexibility and was able to withstand stress from twisting, rolling, and bending. Interestingly, its outstanding flexibility was shown by the researchers by folding the fabric into an origami crane which did not affect the overall electrical performance of the device.

Portable power supply and more

The MEG device has immediate applications due to its ease of scalability and commercially available raw materials. One of the most immediate applications is for use as a portable power source for mobile powering electronics directly by ambient humidity.

"After water absorption, one piece of power-generating fabric that is 1.5 by 2 centimetres in size can provide up to 0.7 volts (V) of electricity for over 150 hours under a constant environment," said research team member Dr Zhang Yaoxin.

The NUS team has also successfully demonstrated the scalability of its new device in generating electricity for different applications. The NUS team connected three pieces of the power-generating fabric together and placed them into a 3D printed case that was the size of a standard AA battery. The voltage of the assembled device was tested to reach as high as 1.96V -- higher than a commercial AA battery of about 1.5V -- which is enough to power small electronic devices such as an alarm clock.

The scalability of the NUS invention, the convenience of obtaining commercially available raw materials as well as the low fabrication cost of about S$0.15 per metre square make the MEG device suitable for mass production.

"Our device shows excellent scalability at a low fabrication cost. Compared to other MEG structures and devices, our invention is simpler and easier for scaling-up integrations and connections. We believe it holds vast promise for commercialisation," shared Asst Prof Tan.

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