Tag Archives: overheating

A Jacket That Breaths: Thins Out with Sweat to Prevent Overheating

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The jacket becomes thicker when it dries (left) and thinner when it gets wet (right)

Xiaofeng Jiang/Nanjing Aviation University Astronaut 2023

If you think you’ll be wearing your jacket indefinitely once the sunshine fades, a material that decreases in thickness when you sweat could be a game changer.

Researchers have previously created self-adaptive materials that help cool individuals in high temperatures by emitting excess heat as infrared radiation. However, these materials generally operate in only one direction and are not effective for retaining warmth in cooler environments.

Xiuqiang Li, a Chinese astronaut, along with his team, has crafted a jacket that consists of layers that dry and flatten when wet. This unique property allows the jacket to become thicker in cooler surroundings and thinner in warmer conditions, primarily due to human perspiration. “The amount of sweat produced serves as a timely and straightforward indicator of the body’s actual thermal needs,” notes Li.

The design of the clothing resembles that of standard down jackets but incorporates layers of cellulose derived from bacteria. This is further bolstered with polyester to ensure that the fabric’s outer layer can expand effectively. Li’s team discovered that the cellulose layer does not dry in a predictable manner and remains fixed at a certain angle for up to 12 hours, working effectively after 200 cycles of transitioning from flat to curved.

The team examined how much heat the material emitted while being worn under varying moisture levels. They found it to feel as cool as standard polyester shirts when wet, yet nearly as warm as down jackets when in a similar condition.

These assessments were akin to wearing the material directly against bare skin. “Theoretically, when the material is layered over other clothing items, such as t-shirts, the sweat produced can permeate through these inner layers, potentially triggering a response that causes thinning,” states Xiaofeng Jiang, who is also from Nanjing Aviation University.

With these insights, the team aims to enhance the fibers to ensure they generate enough warmth to be worn without additional layers.

Li believes that scaling up the production of these materials should be feasible, as bacterial cellulose is readily obtainable and cost-effective; however, the team must first confirm that it can withstand the durability expected from conventional clothing.

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Source: www.newscientist.com

Urban air pollution caused by overheating trees

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Jacaranda tree outside the Los Angeles courthouse

James Brown / Alamy

In Los Angeles, air pollution from cars and human activity is exacerbated by the city's factories emitting chemicals in response to rising temperatures and drought.

“It's difficult to control emissions from factories, [human-caused] “Some.” Eva Fannerstill At the Forschungszentrum Jülich, a German research institute.

From blooming jacaranda trees to fragrant eucalyptus, many plants emit compounds called terpenoids. To plants, these act as chemical signals and function as antioxidants. But in the atmosphere, these volatile organic compounds (VOCs) react with other pollutants to create harmful ozone and particulate pollution called PM2.5.

In areas where cleaner vehicles and electricity generation have reduced man-made sources of air pollution, industrial emissions have begun to play a larger role, but by how much is unclear.

Vannerstill and her colleagues flew planes over Los Angeles over several days in June 2021 to measure the city's VOC emissions. Using an on-board mass spectrometer, the researchers identified concentrations of more than 400 VOCs in the air. Simultaneous 3D measurements of wind speed allowed them to separate molecules rising from the city from those blowing in from elsewhere.

The researchers found that terpenoids made up the majority of VOC emissions in many parts of the city, especially in areas with the most vegetation and on the hottest days. When temperatures exceeded 30°C (86°F), terpenoids made up the majority of emissions, even in the downtown area, where vegetation was sparse and people were more likely to be present.

It's unclear exactly why plants release more terpenoids when temperatures rise, but it could be a response to heat or water stress, Pfannerstill said. Higher temperatures also increase VOC emissions associated with anthropogenic sources, such as gasoline, paint, and even scented personal care products like deodorant and hairspray, possibly due to increased evaporation rates.

The contribution of these personal-care products in particular spikes with population density, suggesting a small but direct link between urban air pollution and citizens' beauty habits. “It's measurable,” Vannerstill says.

The observed relationship between heat and emissions also suggests a pathway through which climate change could exacerbate air pollution: in Los Angeles, the researchers found that a 3°C warming predicted for the city by mid-century could double the impact of VOCs on ozone formation; and its impact on PM2.5 pollution could increase by 40%.

“This direct observation is crucial for building good models to predict what air pollution will be like tomorrow or a few years from now.” Matthew Cogon Jonathan Myers, environmental secretary at the National Oceanic and Atmospheric Administration, said the increase in emissions from factories underscores the importance of further reducing man-made sources of air pollution that react with VOCs, such as nitrous oxide, which comes from burning fossil fuels.

The types of plants planted in cities also have an impact. Roissyne Comanet It's an important consideration as more cities pursue urban greening initiatives. “Vegetation is important,” she says at Columbia University in New York.

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Source: www.newscientist.com