Research led by Brandon Boor at Purdue University found that fragrance compounds released by both conventional cleaners and botanical essential oil-based products can rapidly react indoors and generate nanoparticles. If inhaled, some of these extremely small particles can penetrate deep into the lungs.

The researchers say exposure can be reduced by choosing unscented products, improving ventilation with exhaust fans or open windows, and avoiding devices that generate ozone while scented cleaning products are being used.

The researchers presented their results at the fall meeting of the American Chemical Society (ACS) during the “Healthy Indoor Spaces: Bridging the Microbiome and Chemistry” symposium in McCormick Place.

“Importantly, cleaning removes viruses and bacteria from surfaces, but it can also generate invisible air pollution. There’s no visible dust or smoke in the air, but these particles are forming.” — Brandon Boor

Cleaning Can Create Invisible Nanoparticles

“We showed that indoor ozone reactions with fragrances from cleaning produce nanoparticles that carry a respiratory dose comparable to, or greater than, what you would experience from standing outside along a busy road,” says Boor, an Assistant Professor of Civil and Construction Engineering at Purdue University who studies indoor air quality. “The particles are different in terms of their composition, but the total dose can be higher. You’re not seeing smoke, dust, or haze in the air. Instead, you think the air smells great so it must be clean.”

Boor began investigating how cleaning agents and chemical disinfectants affect indoor environments during the COVID-19 pandemic with his colleague Nusrat Jung, a Purdue Assistant Professor of Civil and Construction Engineering. One feature quickly stood out: many of the products people use to clean and disinfect indoor spaces contain strong fragrances.

“That’s often to create a pleasant smellscape in the indoor space,” says Boor. “But clean air should not smell like highly concentrated citrus fruit. It should not really smell of anything.”

Scientists who study the atmosphere have long known that compounds released by plants can react with ozone. Terpenes such as pinene from pine trees, for example, can participate in reactions that generate tiny airborne particles. Over time, those particles can combine and grow until they become large enough to help seed clouds.

That chemistry proceeds relatively slowly in forests because the amount of terpenes in outdoor air is generally low.

Cleaning Products Release High Levels of Terpenes

Indoors, the situation can be very different. Scented cleaners release terpenes when fragrance compounds evaporate from sprayed droplets or cleaned surfaces.

Cleaning liquids commonly contain compounds including pinene, limonene (lemon), thymol (thyme), and linalool (lavender). Their concentrations during cleaning can be far higher than levels typically measured outdoors. Boor says airborne terpene concentrations inside a room during cleaning can rise to tens or even hundreds of times those found in a forest.

To examine what happens under realistic conditions, the researchers tested scented conventional liquid products as well as botanical-containing disinfectant sprays and wipes inside a model home on Purdue’s campus.

The small house includes a functional kitchen, wood flooring, and a bathroom, allowing the researchers to recreate ordinary household cleaning activities. Their experiments showed that the same basic chemistry responsible for nanoparticle formation outdoors can occur indoors much more rapidly and at much higher concentrations, with potentially important consequences for human exposure.

Billions or Trillions of Particles Can Form

Routine tasks such as mopping floors, spraying countertops, and wiping surfaces with scented products generate billions or trillions of particles, with the total depending on the product.

Most were nanoparticles or ultrafine particles measuring only 1-30 nanometers across. Because particles this small often fall outside the detection range of at-home air quality monitors, people may have no indication that particle concentrations have risen.

The researchers found that ordinary cleaning can temporarily push ultrafine particle levels above those measured outdoors.

Their tiny size is important from a health perspective. Ultrafine particles can settle throughout the respiratory tract and reach deep regions of the lungs. Once there, they can contribute to irritation and inflammation in the respiratory system. Some may also have the potential to enter the bloodstream.

One of the biggest surprises was the speed of the process. Particle formation and growth occurred within just minutes.

“By the time you finish cleaning up an indoor space, you’ve already formed a lot of nanoparticles and inhaled them,” says Boor.

Ozone Can Intensify Indoor Particle Formation

More recently, Boor and Ernest Blatchley, a Professor at Purdue, studied what happens when scented surface cleaners are used at the same time as germicidal far-UV (UV-C) lamps designed to disinfect indoor air.

The combination created particularly favorable conditions for nanoparticle formation.

The lamps interact with oxygen in the air and produce ozone. During experiments in the tiny home, ozone concentrations increased to roughly 20 to 40 parts per billion. Those levels were comparable to, although somewhat below, the outdoor ozone concentrations measured when the experiments were performed.

With both elevated ozone and high concentrations of terpenes present, nanoparticle production became even more intense. That combination raised additional concerns about the amount of particulate matter occupants could inhale.

How to Reduce Exposure While Cleaning

Boor emphasizes that the goal is to help consumers make informed choices rather than discourage cleaning. Cleaning remains important for removing viruses and bacteria from surfaces, but several simple measures may reduce exposure to the secondary pollution produced during the process.

The researchers recommend:

• Choose low-fragrance or fragrance-free products.
• Avoid applying several scented products in the same cleaning session.
• Run exhaust fans or open windows to ventilate the space.
• Do not simultaneously clean surfaces with scented products while using ozone-generating devices, such as far UV-C lamps.

“Importantly, cleaning removes viruses and bacteria from surfaces, but it can also generate invisible air pollution,” says Boor. “There’s no visible dust or smoke in the air, but these particles are forming.”

Boor thanks all the graduate students who have worked with him in the tiny house experiments along with the support of undergraduate students.

The research was funded by a National Science Foundation Faculty Early Career Development Program (CAREER) grant and the Alfred P. Sloan Foundation.

Title Indoor atmospheric nanoparticle formation from scented cleaning products

Abstract Scented volatile chemical products, including surface cleaning agents and botanical disinfectants, are widely used indoors and represent a major source of reactive organic emissions. These products are routinely applied in homes and workplaces for surface cleaning and disinfection to reduce the presence of viruses and bacteria. However, their role in driving indoor atmospheric chemistry and nanoparticle formation remains poorly constrained. This presentation investigates the impact of scented cleaning product use on airborne nanoparticle nucleation, growth, and human exposure to secondary pollutants in indoor environments. Field and laboratory experiments were conducted in controlled residential and office settings using real-time, high-resolution measurements of volatile organic compounds and nanoparticle size distributions extending to the nanocluster aerosol (1-3 nm) regime. Surface cleaning and disinfection activities produced rapid increases in terpene and terpenoid mixing ratios (10-1,000 ppb), often exceeding levels observed in outdoor forested environments. These compounds reacted with indoor oxidants, particularly ozone, to initiate intense nanoparticle nucleation and growth events. Observed nucleation rates (~105 cm^-3 s^-1) and condensational growth rates (up to 300 nm h^-1) exceeded typical outdoor values by orders of magnitude, resulting in transient indoor nanoparticle number concentrations of 10⁵-10⁸ cm^-3. Rapid nanoparticle growth enabled survival to sizes that efficiently deposit throughout the human respiratory system, yielding inhalation dose rates comparable to or exceeding those from primary combustion sources such as traffic emissions. Both conventional and botanical cleaning products generated complex multiphase exposure scenarios involving reactive gases and secondary organic aerosol. These findings identify indoor surface cleaning and disinfection as key drivers of indoor atmospheric nanoparticle formation and highlight the need for improved building ventilation, air cleaning, and product formulation to mitigate exposure to secondary pollutants.

As oxygen levels increased for the first time, enormous amounts of microbial material were buried beneath the seafloor. That burial trapped carbon in rocks and left behind an unusual isotopic signature. For decades, many scientists have interpreted that signature as evidence that Earth’s carbon cycle became dramatically unbalanced on a global scale.

A Famous Signal From Early Earth

Evidence supporting that interpretation has come from drill cores — long cylinders of solid rock pulled from deep underground — recovered from ancient marine sediments in Karelia, Russia, and the Francevillian Basin in Gabon. A new study led by Caltech researchers, however, is raising questions about whether the Russian evidence really records a planetwide event.

“One major debate centers on an unusual carbon-isotope signal that has often been interpreted as evidence of a worldwide environmental change,” says Nivedita Thiagarajan (PhD ’12), a senior scientific researcher at Caltech who works in the lab of John Eiler, the Robert P. Sharp Professor of Geology and Geochemistry and Ted and Ginger Jenkins Leadership Chair of the Division of Geological and Planetary Sciences. “We studied gases trapped in microscopic pockets within rocks from the Zaonega Formation in Karelia, Russia, one of the world’s oldest known fossil oil fields, and found that the carbon-isotope signal at this key site can be explained by local phenomena that occurred in a several-hundred-square-kilometer sedimentary basin rather than across the entire globe.”

Thiagarajan is the lead author of a recent paper published in Geology. The study describes how the researchers reconstructed the sequence of changes preserved in Karelia’s rocks following the first major increase in atmospheric oxygen.

Carbon isotopes — heavier or lighter forms of the element — provide information about the origins of biological material that accumulated billions of years ago. By measuring the relative amounts of these isotopes in drill cores (or carbon-isotope signals), researchers can build a record of ancient environmental change, somewhat like reading the growth rings of a tree.

An unusual carbon signal found in both the Zaonega Formation and rocks from Gabon is known as the Shunga-Francevillian event. Scientists have often pointed to it as evidence that Earth experienced a major global disruption of the carbon cycle around 2 billion years ago.

“Earth, in a way, went crazy during that time interval when oxygen appeared in the atmosphere. What we are trying to assess are the causes and consequences of Earth oxygenation,” explains Aivo Lepland, a researcher at the Geological Survey of Norway (NGU) in Trondheim and a co-author on the study. “This information is archived in the rocks, so, in order to study what happened, you have to study rocks.”

Gases Trapped for 2 Billion Years

To examine the Shunga-Francevillian event from another perspective, the researchers analyzed drill cores stored at NGU. They focused on gases sealed inside microscopic fluid inclusions within samples from the Zaonega Formation that are rich in pyrobitumen.

The Zaonega Formation was once part of a marine sedimentary basin. Pyrobitumen is an insoluble form of organic carbon that develops when buried crude oil or kerogen — a source material for natural gas — is subjected to intense heating deep below the surface.

The project took shape after Lepland arrived at Caltech for a sabbatical. He brought with him a new collection of isotope measurements from gases trapped in Zaonega rocks that had not yet been fully interpreted.

At the same time, Thiagarajan and Eiler had recently finished research measuring isotope ratios in natural gases. That work had helped them develop a broader framework for understanding how natural gas forms.

When the researchers combined the two sets of expertise and data, a different explanation for the ancient isotope signatures began to emerge.

Magma, Methane, and Microbes

The team proposes that a sheet of magma forced its way through layers of marine sediment at the Zaonega Formation, which at the time lay beneath a prehistoric ocean. Heat from the magma warmed sediments packed with organic material.

That heating generated hydrocarbons including methane and propane. The gases then moved upward through the sediment and eventually reached microbes living near the seafloor that consumed methane.

Those microbes produced biomass carrying a light carbon isotope signature, potentially explaining the unusual signal preserved in the rocks.

The temperature evidence supports this scenario. The researchers identified a large thermal gradient, with temperatures reaching approximately 350 degrees Celsius beside the magma intrusion and falling to about 72 degrees Celsius at an ancient seafloor asphalt spill roughly 300 meters higher.

“This chain of geological and biological processes can account for the unusual carbon-isotope signal recorded at the Zaonega Formation,” Thiagarajan says. “It was interesting to see that some of the same signatures that we observe in modern oil and gas basins are also there and preserved in 2-billion-year-old samples.”

The researchers emphasize that they cannot completely rule out contributions from other processes. Even so, their results indicate that the carbon isotope anomaly preserved at Zaonega was driven mainly by events within the local sedimentary basin rather than by a global disturbance.

“Because Zaonega is a reference site for the Shunga-Francevillian event, our findings raise important questions about whether it should be considered a worldwide event,” says Thiagarajan.

Testing the Theory in Gabon

The next step will be to determine whether the same explanation can account for the similar isotope signal found in Gabon.

Researchers plan to analyze samples collected through the GOE-DEEP project, co-funded by the International Continental Scientific Drilling Program. The goal is to test whether local geological and biological processes like those identified in Russia also shaped the Gabonese rock record.

In the summer of 2025, Lepland spent four months in Gabon coordinating the drilling campaign. The newly recovered cores arrived at NGU in February and are scheduled to be sampled later this year by an international research team representing 18 countries.

“Now we can really put things together by doing a similar type of study on the Gabonese rocks to compare the two sites,” Lepland says. “This is how science moves forward.”

The Geology paper is titled “Paleoproterozoic thermogenic hydrocarbon generation, Zaonega Formation, Russia.” Additional authors on the study are Florian Eichinger of Hydroisotop GmbH, a natural isotope analysis laboratory in Germany, and Anthony Prave of the University of St. Andrews in Scotland.

According to the researchers, the findings provide new clues about how tirzepatide works and could help guide the development of broader treatments for obesity and other metabolic disorders.

The research was led by Marion Peyrou, Ramón y Cajal researcher at the Faculty of Biology and the Institute of Biomedicine of the University of Barcelona (IBUB), the Sant Joan de Déu Research Institute (IRSJD) and the CIBER in Physiopathology of Obesity and Nutrition (CIBEROBN).

Tirzepatide Targets Two Hormone Receptors

Tirzepatide (generic name of the drug Mounjaro) is approved for weight management in adults with obesity or overweight with comorbidities, as well as for treating poorly controlled type 2 diabetes mellitus.

Unlike some other obesity medications, tirzepatide targets the receptors for two hormonal factors at the same time: GIP and GLP-1. This dual mechanism can produce substantial weight loss, largely because the drug reduces food intake.

Researchers wanted to determine whether tirzepatide also produces metabolic changes that cannot be explained simply by eating less.

To investigate, the team examined how the drug affected different fat deposits in an experimental mouse model, since this kind of detailed tissue analysis cannot readily be performed in humans. Obese mice — fed a high-fat diet — were treated with tirzepatide.

The researchers then compared those animals with mice that did not receive the drug but were given the same amount of food. By controlling food intake this way, the scientists could distinguish changes caused directly by tirzepatide from those resulting from reduced calorie consumption.

Mounjaro Activates Calorie-Burning Brown Fat

The analysis showed that tirzepatide activated brown adipose tissue. Unlike white adipose tissue, which primarily stores fat and tends to accumulate in obesity, brown fat specializes in using energy and ‘burning’ calories from food.

“This activation is associated with an increased capacity to burn metabolic energy and with the production of batokines by brown adipose tissue, molecules that are beneficial for metabolism,” says Marion Peyrou.

The finding suggests that tirzepatide may influence metabolism in ways that extend beyond the weight loss caused by appetite suppression and reduced food intake.

“This drug not only reduces body weight, but also has beneficial effects on metabolism. Active brown adipose tissue ‘burns’ glucose and fat within the body, which would contribute to its positive effect not only in reducing body weight, but also in lowering blood glucose and fat levels, and improving metabolism,” the researcher points out.

A Broader Strategy for Treating Obesity

Scientists have long viewed brown fat activation as a potentially useful strategy for treating obesity and other metabolic diseases. However, previous efforts to activate brown adipose tissue with drugs have often been unsuccessful because of unwanted side effects, particularly those affecting the heart.

“Tirzepatide, although it activates brown adipose tissue, does not have these negative effects; on the contrary, it shows cardiovascular benefits. If our findings are confirmed in humans, it would reinforce the importance of developing therapeutic strategies that not only reduce food intake but also increase energy expenditure and brown fat activation,” explains the researcher.

The results support the idea that obesity therapies may be more effective when they target several physiological processes at once instead of focusing only on appetite.

“This could help improve weight control and reduce associated disorders, such as type 2 diabetes and other metabolic disorders,” she adds.

Toward More Personalized Obesity Treatment

A clearer picture of how tirzepatide works could also influence how drugs in this class are prescribed in the future.

“Identifying which patient profiles could benefit most, for example those with more compromised energy expenditure, would open the door to more personalized medicine, based not only on appetite or weight control, but also on overall metabolic status,” she emphasizes.

The researchers caution, however, that the findings come from mice and cannot yet be assumed to apply in the same way to people. Human and mouse metabolism can differ substantially, as can the distribution of fat tissue and responses to medications.

“As this is a study conducted on mice, we must be cautious, as there may be significant differences between species in terms of metabolism regulation, adipose tissue distribution and response to drugs. Therefore, we need more clinical evidence on the action of these drugs on fat in humans,” concludes Peyrou.

Sleep offers a useful way to study that question. Although the body is resting, the brain remains active, especially during rapid eye movement (REM) sleep, which is closely associated with dreaming and memory processing. REM sleep is often described as “paradoxical sleep” because the body is mostly still while brain activity resembles wakefulness.

Researchers at Tohoku University have now identified another REM sleep paradox. During this stage, the apparent energy supply to the dreaming brain increases, yet levels of the energy molecule neurons directly use actually decline.

The findings were published in Communications Biology.

“Ever felt exhausted after a vivid dream?” asks Professor Ko Matsui of Tohoku University. “Sleep may appear peaceful, but the brain is highly active — especially when dreaming. We were intrigued by this paradox, and wanted to look into the scientific basis behind why dreaming is somehow tiring.”

Watching the Sleeping Brain in Real Time

To investigate what happens to brain energy during sleep, the researchers used a UV-curable resin to keep the skulls of mice transparent, allowing them to observe the brain during natural sleep.

Using wide-field fluorescence imaging, they tracked changes in brain blood volume as a sign of incoming “fuel” supply. They also measured neuronal ATP, the energy molecule that powers neurons, along with astrocytic pyruvate, a key compound that connects glucose from the blood with energy metabolism in the brain.

Non-REM sleep is well known for strong neuronal activity in the delta-band frequency, but smaller theta-band fluctuations also occur. The researchers found that these theta-band changes could predict shifts in brain blood volume several seconds later. That pattern suggests the sleeping brain adjusts its blood vessels in response to changing neuronal activity and metabolic demand.

The Brain Prepares for REM Sleep in Advance

A different pattern appeared as the brain moved from non-REM sleep into REM sleep.

About 50 seconds before the classically defined beginning of REM sleep, brain blood volume started to increase. The change began in the posterior cortex and then moved forward, pointing to a large-scale process that may prepare the brain metabolically for REM sleep.

Once REM sleep began, astrocytic pyruvate also rose. That increase was consistent with either greater availability of metabolic fuel or increased glycolytic activity in astrocytes.

But at the same time, neuronal ATP fell.

Why Does Neuronal Energy Drop During Dreams?

There are several possible explanations for this decrease in ATP.

Neurons may use large amounts of ATP during REM sleep to support memory-related synaptic reorganization, communication between the hippocampus and cortex, or broad transitions across brain circuits.

Another possibility is that the transfer of metabolic resources from astrocytes to neurons changes during REM sleep. Mitochondrial production of ATP could also shift during this stage.

Whatever the mechanism, the findings suggest that the dreaming brain may be operating under unusually high energy demands even while its fuel supply increases.

A Broader Lesson About the Brain’s Energy Economy

The results may also reveal something more fundamental about biological computation.

Unlike conventional computers, animal brains must operate within strict metabolic limits. Rather than supplying energy evenly across the brain, the nervous system may redirect resources depending on behavioral state, memory demands, and other internal needs.

“Understanding how the brain balances energy supply and consumption may help explain what makes biological intelligence so efficient,” explains lead investigator Yusuke Takahashi. “REM sleep gives us a natural example of how the brain reorganizes its energy economy to support complex internal processing.”

Sleep plays a critical role in functions such as memory consolidation and maintaining mental performance the following day. By revealing how energy supply and energy use shift during REM sleep, the research adds another piece to the puzzle of why sleep is so important not only for the body, but also for the brain.

Some of the most important are known as inner triplets. These groups of three quadrupole magnets (hence the name) sit on both sides of the LHC’s four main experiments. Their job is to focus the particle beams as tightly as possible just before the particles collide inside the detectors.

The tighter the beams are “compressed,” the greater the chance that particles will collide. That makes the inner triplets essential for increasing the LHC’s luminosity, i.e. the number of collisions that occur in a given period of time. More luminosity means more collisions, giving researchers more data to analyze.

Preparing the LHC for a New Era

A major part of the future High-Luminosity LHC (HiLumi LHC) project involves replacing the existing inner triplets with a much more powerful generation of magnets.

The work is taking place during the third long shutdown (LS3). Reently, crews cut the first magnet interconnection, formally beginning the replacement operation. CERN Director-General Mark Thomson also visited LHC Point 1 (the ATLAS experiment) to mark the milestone.

“The replacement of these magnets with the new HiLumi LHC inner triplets is crucial for the coming high-luminosity years. The first quadrupole of the new triplets should arrive in the tunnel at the start of 2029. In total, 16 cryostats and 28 cryo-assemblies will be installed – a major undertaking,” explains Jean-Philippe Tock, Head of the LS3 Coordination Team.

Magnets About 40% Stronger

The new inner triplets are the product of years of research and development. They represent a major technological advance over the niobium-titanium magnets currently operating inside the LHC.

Instead of niobium-titanium, the upgraded magnets use niobium-tin superconducting coils. This allows them to generate magnetic fields reaching 11.3 tesla, about 40% stronger than the fields produced by the current magnets.

The new equipment will be installed around the ATLAS and CMS experiments, where the increased collision rate will be especially important.

ALICE and LHCb operate differently and pursue different physics programs, so they do not need the same increase in instantaneous luminosity. Their existing inner triplets can therefore remain in place. However, those magnets will still be upgraded so that both experiments can benefit from the overall increase in luminosity.

Removing 28 Superconducting Magnets

Since September 7, CERN teams have been dismantling sections of the collider on either side of ATLAS and CMS. The goal is to remove 28 superconducting magnets (including the inner triplets) that are scheduled to be replaced.

The operation marks the end of an era for hardware that has been part of the LHC since its construction.

“Today’s event is a major milestone for CERN, especially for the HiLumi LHC project team. The current inner triplets date back to the LHC construction phase and were installed in the machine between 2005 and 2007. After nearly twenty years of operation, they will give way to a new generation of even more powerful magnets. It’s truly remarkable to witness such a handover from one generation of innovation to the next,” says Markus Zerlauth, the HiLumi LHC Project Leader.