“Combustion remains a source of air pollution across the world, both indoors and outdoors. We found that cooking on your gas stove produces large amounts of small nanoparticles that get into your respiratory system and deposit efficiently,” said Brandon Boor, an associate professor in Purdue’s Lyles School of Civil Engineering, who led this research.

Based on these findings, the researchers would encourage turning on a kitchen exhaust fan while cooking on a gas stove.

The study, published in the journal PNAS Nexus, focused on tiny airborne nanoparticles that are only 1-3 nanometers in diameter, which is just the right size for reaching certain parts of the respiratory system and spreading to other organs.

Recent studies have found that children who live in homes with gas stoves are more likely to develop asthma. But not much is known about how particles smaller than 3 nanometers, called nanocluster aerosol, grow and spread indoors because they’re very difficult to measure.

“These super tiny nanoparticles are so small that you’re not able to see them. They’re not like dust particles that you would see floating in the air,” Boor said. “After observing such high concentrations of nanocluster aerosol during gas cooking, we can’t ignore these nano-sized particles anymore.”

Using state-of-the-art air quality instrumentation provided by the German company GRIMM AEROSOL TECHNIK, a member of the DURAG GROUP, Purdue researchers were able to measure these tiny particles down to a single nanometer while cooking on a gas stove in a “tiny house” lab. They collaborated with Gerhard Steiner, a senior scientist and product manager for nano measurement at GRIMM AEROSOL.

Called the Purdue zero Energy Design Guidance for Engineers (zEDGE) lab, the tiny house has all the features of a typical home but is equipped with sensors for closely monitoring the impact of everyday activities on a home’s air quality. With this testing environment and the instrument from GRIMM AEROSOL, a high-resolution particle size magnifier — scanning mobility particle sizer (PSMPS), the team collected extensive data on indoor nanocluster aerosol particles during realistic cooking experiments.

This magnitude of high-quality data allowed the researchers to compare their findings with known outdoor air pollution levels, which are more regulated and understood than indoor air pollution. They found that as many as 10 quadrillion nanocluster aerosol particles could be emitted per kilogram of cooking fuel — matching or exceeding those produced from vehicles with internal combustion engines.

This would mean that adults and children could be breathing in 10-100 times more nanocluster aerosol from cooking on a gas stove indoors than they would from car exhaust while standing on a busy street.

“You would not use a diesel engine exhaust pipe as an air supply to your kitchen,” said Nusrat Jung, a Purdue assistant professor of civil engineering who designed the tiny house lab with her students and co-led this study.

Purdue civil engineering PhD student Satya Patra made these findings by looking at data collected in the tiny house lab and modeling the various ways that nanocluster aerosol could transform indoors and deposit into a person’s respiratory system.

The models showed that nanocluster aerosol particles are very persistent in their journey from the gas stove to the rest of the house. Trillions of these particles were emitted within just 20 minutes of boiling water or making grilled cheese sandwiches or buttermilk pancakes on a gas stove.

Even though many particles rapidly diffused to other surfaces, the models indicated that approximately 10 billion to 1 trillion particles could deposit into an adult’s head airways and tracheobronchial region of the lungs. These doses would be even higher for children — the smaller the human, the more concentrated the dose.

The nanocluster aerosol coming from the gas combustion also could easily mix with larger particles entering the air from butter, oil or whatever else is cooking on the gas stove, resulting in new particles with their own unique behaviors.

A gas stove’s exhaust fan would likely redirect these nanoparticles away from your respiratory system, but that remains to be tested.

“Since most people don’t turn on their exhaust fan while cooking, having kitchen hoods that activate automatically would be a logical solution,” Boor said. “Moving forward, we need to think about how to reduce our exposure to all types of indoor air pollutants. Based on our new data, we’d advise that nanocluster aerosol be considered as a distinct air pollutant category.”

This study was supported by a National Science Foundation CAREER award to Boor. Additional financial support was provided by the Alfred P. Sloan Foundation’s Chemistry of Indoor Environments program through an interdisciplinary collaboration with Philip Stevens, a professor in Indiana University’s Paul H. O’Neill School of Public and Environmental Affairs in Bloomington.

According to the Ancient Greek philosopher Pythagoras, ‘consonance’ — a pleasant-sounding combination of notes — is produced by special relationships between simple numbers such as 3 and 4. More recently, scholars have tried to find psychological explanations, but these ‘integer ratios’ are still credited with making a chord sound beautiful, and deviation from them is thought to make music ‘dissonant’, unpleasant sounding.

But researchers from Cambridge University, Princeton and the Max Planck Institute for Empirical Aesthetics, have now discovered two key ways in which Pythagoras was wrong.

Their study, published in Nature Communications, shows that in normal listening contexts, we do not actually prefer chords to be perfectly in these mathematical ratios.

“We prefer slight amounts of deviation. We like a little imperfection because this gives life to the sounds, and that is attractive to us,” said co-author, Dr Peter Harrison, from Cambridge University’s Faculty of Music and Director of its Centre for Music and Science.

The researchers also found that the role played by these mathematical relationships disappears when you consider certain musical instruments that are less familiar to Western musicians, audiences and scholars. These instruments tend to be bells, gongs, types of xylophones and other kinds of pitched percussion instruments. In particular, they studied the ‘bonang’, an instrument from the Javanese gamelan built from a collection of small gongs.

“When we use instruments like the bonang, Pythagoras’s special numbers go out the window and we encounter entirely new patterns of consonance and dissonance,” Dr Harrison said.

“The shape of some percussion instruments means that when you hit them, and they resonate, their frequency components don’t respect those traditional mathematical relationships. That’s when we find interesting things happening.”

“Western research has focused so much on familiar orchestral instruments, but other musical cultures use instruments that, because of their shape and physics, are what we would call ‘inharmonic’.

The researchers created an online laboratory in which over 4,000 people from the US and South Korea participated in 23 behavioural experiments. Participants were played chords and invited to give each a numeric pleasantness rating or to use a slider to adjust particular notes in a chord to make it sound more pleasant. The experiments produced over 235,000 human judgments.

The experiments explored musical chords from different perspectives. Some zoomed in on particular musical intervals and asked participants to judge whether they preferred them perfectly tuned, slightly sharp or slightly flat. The researchers were surprised to find a significant preference for slight imperfection, or ‘inharmonicity’. Other experiments explored harmony perception with Western and non-Western musical instruments, including the bonang.

Instinctive appreciation of new kinds of harmony

The researchers found that the bonang’s consonances mapped neatly onto the particular musical scale used in the Indonesian culture from which it comes. These consonances cannot be replicated on a Western piano, for instance, because they would fall between the cracks of the scale traditionally used.

“Our findings challenge the traditional idea that harmony can only be one way, that chords have to reflect these mathematical relationships. We show that there are many more kinds of harmony out there, and that there are good reasons why other cultures developed them,” Dr Harrison said.

Importantly, the study suggests that its participants — not trained musicians and unfamiliar with Javanese music — were able to appreciate the new consonances of the bonang’s tones instinctively.

“Music creation is all about exploring the creative possibilities of a given set of qualities, for example, finding out what kinds of melodies can you play on a flute, or what kinds of sounds can you make with your mouth,” Harrison said.

“Our findings suggest that if you use different instruments, you can unlock a whole new harmonic language that people intuitively appreciate, they don’t need to study it to appreciate it. A lot of experimental music in the last 100 years of Western classical music has been quite hard for listeners because it involves highly abstract structures that are hard to enjoy. In contrast, psychological findings like ours can help stimulate new music that listeners intuitively enjoy.”

Exciting opportunities for musicians and producers

Dr Harrison hopes that the research will encourage musicians to try out unfamiliar instruments and see if they offer new harmonies and open up new creative possibilities.

“Quite a lot of pop music now tries to marry Western harmony with local melodies from the Middle East, India, and other parts of the world. That can be more or less successful, but one problem is that notes can sound dissonant if you play them with Western instruments.

“Musicians and producers might be able to make that marriage work better if they took account of our findings and considered changing the ‘timbre’, the tone quality, by using specially chosen real or synthesised instruments. Then they really might get the best of both worlds: harmony and local scale systems.”

Harrison and his collaborators are exploring different kinds of instruments and follow-up studies to test a broader range of cultures. In particular, they would like to gain insights from musicians who use ‘inharmonic’ instruments to understand whether they have internalised different concepts of harmony to the Western participants in this study.

The report, “Endocrine Disrupting Chemicals: Threats to Human Health” provides a comprehensive update on the state of the science around EDCs, with increasing evidence that this large group of toxic substances may be implicated in rising global health concerns.

The report from the Endocrine Society, co-produced with the International Pollutants Elimination Network (IPEN), includes detailed analyses on exposure to EDCs from four sources: plastics, pesticides, consumer products (including children’s products), and per-and polyfluoroalkyl substances (PFAS), a class of thousands of chemicals known or suspected to be EDCs.

The Endocrine Society-IPEN report is being released during the U.N. Environment Assembly (UNEA-6) meeting in Nairobi. At UNEA key agenda items include welcoming the newly adopted Global Framework on Chemicals, advancing global action on highly hazardous pesticides, and threats to the circular economy from plastics and toxic chemicals. The groups’ report anticipates an update from UNEP and the WHO expected later this year on their 2012 Report on State of the Science of Endocrine Disrupting Chemicals.

“A well-established body of scientific research indicates that endocrine-disrupting chemicals that are part of our daily lives are making us more susceptible to reproductive disorders, cancer, diabetes, obesity, heart disease, and other serious health conditions,” said the report’s lead author, Andrea C. Gore, PhD, of the University of Texas at Austin. Gore is also a member of the Endocrine Society’s Board of Directors. “These chemicals pose particularly serious risks to pregnant women and children. Now is the time for the UN Environment Assembly and other global policymakers to take action to address this threat to public health.”

Hormones are natural chemicals that contribute to normal development, adaptation, and maintenance of bodily processes and health. By interfering with hormones and their actions, EDC exposure can impact many health-related functions, with consequences for increased risks of many serious conditions. Evidence suggests that EDCs in the environment contribute to disorders such as diabetes, neurological disorders, reproductive disorders, inflammation, and compromised immune functioning.

Two of the four analyses in the report look at EDCs used in plastics and as pesticides. Global production of plastics and pesticides is increasing even as scientists warn that chemical and plastic pollution is an escalating crisis. Glyphosate is the world’s most widely used herbicide, and a recent study found that glyphosate has eight of ten key characteristics of an EDC. Other studies have found links between glyphosate and adverse reproductive health outcomes. Plastics are made with thousands of known toxic substances, some of which are known or suspected EDCs. The report examines bisphenols and phthalates, two toxic chemical groups found in many plastics. Exposures to EDCs from plastics occur at all phases of plastics production, use, disposal, and even from recycled plastics.

The Endocrine Society-IPEN report notes that, while evidence of health threats from EDCs is mounting, current regulations have not kept pace. “EDCs are different than other toxic chemicals, but most regulations fail to address these differences,” said IPEN Science Advisor Sara Brosché, Ph.D. “For example, we know that even very low doses of endocrine disrupting chemicals can cause health problems and there may be no safe dose for exposure to EDCs. However, regulations typically do not protect against low-dose effects. We need a global approach to controlling EDCs based on the latest science with a goal of protecting the human right to a healthy environment.”

At the UNEA-6 meeting, IPEN is also releasing a new report on “The Global Threat from Highly Hazardous Pesticides,” highlighting ongoing health and environmental risks from HHPs, especially in low- and middle-income countries. DDT, glyphosate, and chorpyrifos, three HHPs reviewed in the Endocrine Society report, are also highlighted in the new IPEN report as they continue to pose health threats especially in the Global South.

In addition to plastics and pesticides, the report looks at EDC exposures from arsenic and lead, and from widely used per- and polyfluoroalkyl substances (PFAS), humanmade “forever chemicals” used as oil and water repellents and coatings. Lead remains in use in paint in many countries, as documented in recent IPEN reports. Endocrine-related conditions from lead exposure may include delayed onset of puberty and early menopause. Arsenic is a common metal that has long been linked to cancer and other health conditions, and more recent evidence shows that arsenic can disrupt multiple endocrine systems. PFAS are used in hundreds of products including clothing and food packaging, but recent studies show that some PFAS can disrupt hormones such as estrogen and testosterone and impair thyroid hormone functions.

The record results from a collaboration between the company First Solar European Technology Center (formerly known as Evolar) and solar cell researchers at Uppsala University.

“The measurements that we have made ourselves for this solar cell and other solar cells produced recently are within the margin of error for the independent measurement. That measurement will also be used for an internal calibration of our own measurement methods,” says Marika Edoff, Professor of Solar Cell Technology at Uppsala University, who is responsible for the study.

The previous world record was 23.35 per cent (Solar Frontier, Japan), preceded by 22.9 per cent (ZSW, Germany). Uppsala University has held the record before, the first time being in the 1990s in the research collaboration Euro-CIS.

“At one time we also held the record for a series-connected prototype. Even though it’s quite a long time since we held the cell record, we’ve often been just behind the best results and of course there are many relevant aspects to consider, such as the potential for scaling up to a large-scale process, where we have always been at the forefront,” Edoff says.

Solar cells are increasing rapidly worldwide and solar power accounted for just over 6 per cent of electricity around the globe in 2022 according to the International Energy Agency (IEA). The best solar modules of crystalline silicon, which is the most widely used material in solar cells, currently convert more than 22 per cent of sunlight to electric power and modern solar cells are both low cost and stable in the long term.

One target in solar cell research is to attain more than 30 per cent efficiency with reasonable production costs. The focus is very often on tandem solar cells, as being more efficient, but so far they have been too costly for large-scale use.

The world record of 23.64 per cent has been measured by the independent institute Fraunhofer ISE in Germany. The scholarly paper presents a thorough material and electrical analysis of the solar cell as well as a comparison with previous records for the same type of solar cell from other research institutions.

A solar cell’s most important properties are the ability to absorb light and the ability to transport energy to an electrical load. For this to succeed, the material must be able to absorb an optimal portion of sunlight while avoiding wasting this energy by converting it into heat within the solar cell.

CIGS solar cells consist of a glass sheet made of normal window glass that has been coated with several different layers, each of which has a specific task. The material that absorbs the sunlight consists of copper, indium, gallium and selenide (hence the acronym CIGS), with additions of silver and sodium. This layer is placed in the actual solar cell, between a back contact of metallic molybdenum and a transparent front contact. To make the solar cell as efficient as possible in separating out electrons, the CIGS layer is treated with rubidium fluoride. The balance between the two alkali metals, sodium and rubidium, and the composition of the CIGS layer are key to the conversion efficiency, i.e. the share of the complete solar spectrum that is converted to electric power in the solar cell.

When measurement institutes conduct their tests, they measure the solar cell efficiency using filtered light that mimics the sun in both intensity and spectrum. During measurement, the solar cell is kept at a controlled temperature and the independent institutes regularly send calibration solar cells to one another. To be registered as a world record, an independent measurement is required, which in this case was carried out by the measurement institute Fraunhofer ISE.

“Our study demonstrates that CIGS thin-film technology is a competitive alternative as a stand-alone solar cell. The technology also has properties that can function in other contexts, such as the bottom cell of a tandem solar cell,” Edoff says.

Several advanced measurement methods have been used to further understand the correlation between the efficiency and the solar cell structure: material from the solar cell has been characterised by nano-XRF (X-ray fluorescence spectroscopy) at the MAX IV facility in Lund, where a careful compositional analysis has been made. Transmission electron microscopy (TEM) at high resolution has been used to study cross sections of the solar cell, both composition as a function of depth and how the crystal grains are built up, as well as the interfaces between the layers. Using photoluminescence, the spectrum of the light emitted by the solar cell after excitation by a laser has been studied as a means to understanding how well the solar cell takes care of electrons internally. A solar cell that shines brightly has a lower share of internal heat losses than a solar cell that shines faintly. Finally, electrical measurement methods have been used to analyse the doping of the CIGS material.

“The fact that we now hold the world record means a lot for both Uppsala University and First Solar European Technology Center. For the CIGS technology, which is known for high reliability, a world record also means that it may offer a viable alternative for new applications in e.g. tandem solar cells. This is important for our research colleagues around the world. We hope that the analyses of the material and electric properties will provide a basis for further improvements in performance,” Edoff concludes.

“It is well known that some white dwarfs — slowly cooling embers of stars like our Sun — are cannibalising pieces of their planetary systems. Now we have discovered that the star’s magnetic field plays a key role in this process, resulting in a scar on the white dwarf’s surface,” says Stefano Bagnulo, an astronomer at Armagh Observatory and Planetarium in Northern Ireland, UK, and lead author of the study.

The scar the team observed is a concentration of metals imprinted on the surface of the white dwarf WD 0816-310, the Earth-sized remnant of a star similar to, but somewhat larger than, our Sun. “We have demonstrated that these metals originate from a planetary fragment as large as or possibly larger than Vesta, which is about 500 kilometres across and the second-largest asteroid in the Solar System,” says Jay Farihi, a professor at University College London, UK, and co-author on the study.

The observations also provided clues to how the star got its metal scar. The team noticed that the strength of the metal detection changed as the star rotated, suggesting that the metals are concentrated on a specific area on the white dwarf’s surface, rather than smoothly spread across it. They also found that these changes were synchronised with changes in the white dwarf’s magnetic field, indicating that this metal scar is located on one of its magnetic poles. Put together, these clues indicate that the magnetic field funneled metals onto the star, creating the scar.*

“Surprisingly, the material was not evenly mixed over the surface of the star, as predicted by theory. Instead, this scar is a concentrated patch of planetary material, held in place by the same magnetic field that has guided the infalling fragments,” says co-author John Landstreet, a professor at Western University, Canada, who is also affiliated with the Armagh Observatory and Planetarium. “Nothing like this has been seen before.”

To reach these conclusions, the team used a ‘Swiss-army knife’ instrument on the VLT called FORS2, which allowed them to detect the metal scar and connect it to the star’s magnetic field. “ESO has the unique combination of capabilities needed to observe faint objects such as white dwarfs, and sensitively measure stellar magnetic fields,” says Bagnulo. In their study, the team also relied on archival data from the VLT’s X-shooter instrument to confirm their findings.

Harnessing the power of observations like these, astronomers can reveal the bulk composition of exoplanets, planets orbiting other stars outside the Solar System. This unique study also shows how planetary systems can remain dynamically active, even after ‘death’.

Notes

* Previously, astronomers have observed numerous white dwarfs polluted by metals that were scattered over the surface of the star. These are known to originate from disrupted planets or asteroids that veer too close to the star, following star-grazing orbits similar to those of comets in our Solar System. However, for WD 0816-310, the team is confident that vaporised material was ionised and guided onto the magnetic poles by the white dwarf’s magnetic field. The process shares similarities to how auroras form on Earth and on Jupiter.