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To Help Cool a Hot Planet, the Whitest of White Coats Scientists at Purdue have created a white paint that, when applied, can reduce the surface temperature on a roof and cool the building beneath it.

Superwhite paint can cool buildings even in hot sunlight

Xiulin Ruan, a professor of mechanical engineering at Purdue University, didn’t set out to make it into the Guinness World Records when he began trying to make a new type of paint. He had a loftier goal: to cool down buildings without torching the Earth.

In 2020, Dr. Ruan and his team unveiled their creation: a type of white paint that can act as a reflector, bouncing 95 percent of the sun’s rays away from the Earth’s surface, up through the atmosphere and into deep space. A few months later, they announced an even more potent formulation that increased sunlight reflection to 98 percent.

The paint’s properties are almost superheroic. It can make surfaces as much as eight degrees Fahrenheit cooler than ambient air temperatures at midday, and up to 19 degrees cooler at night, reducing temperatures inside buildings and decreasing air-conditioning needs by as much as 40 percent. It is cool to the touch, even under a blazing sun, Dr. Ruan said. Unlike air-conditioners, the paint doesn’t need any energy to work, and it doesn’t warm the outside air.

In 2021, Guinness declared it the whitest paint ever, and it’s since collected several awards. While the paint was originally envisioned for rooftops, manufacturers of clothes, shoes, cars, trucks and even spacecraft have come clamoring. Last year, Dr. Ruan and his team announced that they’d come up with a more lightweight version that could reflect heat from vehicles.

“We weren’t really trying to develop the world’s whitest paint,” Dr. Ruan said in an interview. “We wanted to help with climate change, and now it’s more of a crisis, and getting worse. We wanted to see if it was possible to help save energy while cooling down the Earth.”

While the paint is officially the world’s whitest, it isn’t blindingly so because it scatters light, Dr. Ruan said. It doesn’t look all that different from white paint from the hardware store.

The paint is at least a year from being ready for commercial use, and work is underway to increase its durability and dirt resistance. Dr. Ruan said the Purdue[1] team has partnered with a company, but can’t yet name it. The team is also developing colored paints that use the ultrawhite as a base. “They will work less ideally than the white, but better than some of the other commercial colours,” he said.

As the climate crisis worsens, scientists have been urgently working to develop reflective materials, including different types of coatings and films, that could passively cool the Earth. The materials rely on principles of physics that allow thermal energy to travel from Earth along specific wavelengths through what’s known as the transparency or sky window in the atmosphere, and out into deep space.

Jeremy Munday, a professor of electrical and computer engineering at the University of California[2], Davis[3], who researches clean technology, said this redirection would barely affect space. The sun already emits more than a billion times more heat than the Earth, he said, and this method merely reflects heat already generated by the sun. “It’d be like pouring a cup of regular water into the ocean,” Dr. Munday said.

He calculated that if materials such as Purdue’s ultra-white paint were to coat between 1 percent and 2 percent of the Earth’s surface, slightly more than half the size of the Sahara, the planet would no longer absorb more heat than it was emitting, and global temperatures would stop rising.

Dr. Munday noted that covering half the Sahara, or any contiguous surface, with that much radiative material shouldn’t happen for a number of reasons, among them practicality, wildlife concerns and weather disruptions caused by one region suddenly becoming much cooler.

But spreading radiative cooling spots around the world could have global and local benefits, such as offsetting the urban heat island effect, which occurs because most buildings absorb and trap much more heat than natural surfaces like woodlands, water and plants.

While humans in such hot and picturesque places as Santorini[4] and the aptly named Casablanca[5] have long used white paint to cool dwellings, and municipalities are increasingly looking to paint rooftops white, Dr. Ruan said commercial white paints generally reflect 80 percent to 90 percent of sunlight. This means they still absorb 10 percent to 20 percent of the heat, which in turn warms surfaces and the ambient air. The Purdue paint, by comparison, absorbs so much less solar heat and radiates so much more heat into deep space that it cools surfaces to below-ambient temperatures.

Still, there are concerns. The standard version of Purdue’s ultrawhite paint uses barium sulfate[6], which has to be mined, driving up its carbon footprint, though Dr. Ruan noted that titanium dioxide[7], which is used in the vast majority of commercial paints, also has to be mined.

Geoengineering — manipulating different processes to control the Earth’s climate — has also been criticised for distracting from the root problem: Humans must stop burning fossil fuels to avoid more catastrophic effects of climate change. But even if all fossil fuel use stopped immediately, climate disasters would continue to unfold because of the amount of greenhouse gases that are trapped in the atmosphere. Large-scale radiative cooling, Dr. Munday said, would be akin to a life raft.

“This is definitely not a long-term solution to the climate problem,” Dr. Munday said. “This is something you can do short term to mitigate worse problems while trying to get everything under control.”

The Far-Reaching Effects of Extreme Heat

China’s Addiction to Coal: While pledging to reduce carbon emissions, China is greatly increasing its use of coal to generate electricity for air-conditioning during heat waves.

Traveling to Europe: The top tourist destinations of Italy, Spain and Greece are sweltering this summer. Travelers can take precautionary measures to protect themselves.

Historic Heat: Phoenix[8] is trying to adapt to a new reality of chronic extreme heat. Its chief heat officer told The Daily how the city is adjusting to it.

A Vulnerable Population: The dangerous heat sweeping across the United States and Europe has posed particular perils for older adults. Here is how they can stay safe.

Source

Cara Buckley, To Help Cool a Hot Planet, the Whitest of White Coats Scientists at Purdue have created a white paint that, when applied, can reduce the surface temperature on a roof and cool the building beneath it, in: New York Times, 12-07-2023, https://www.nytimes.com/2023/07/12/climate/white-paint-climate-cooling.html?smid=nytcore-ios-share&referringSource=articleShare

[1] Purdue University (or simply Purdue) is a public land-grant research university in West Lafayette, Indiana, and the flagship campus of the Purdue University system. The university was founded in 1869 after Lafayette businessman John Purdue donated land and money to establish a college of science, technology, and agriculture in his name. The first classes were held on September 16, 1874, with six instructors and 39 students. It has been ranked as among the best public universities in the United States by major institutional rankings, and is known for its engineering program.

[2] The University of California opened its doors in 1869 with just 10 faculty members and 40 students. Today, the UC system has more than 280,000 students and 227,000 faculty and staff, with 2.0 million alumni living and working around the world. From UC Davis to UC San Diego, nine of our campuses house undergraduate and graduate education. UC San Francisco focuses on health education and it only offers graduate degrees. https://www.universityofcalifornia.edu/

[3] Davis is the ultimate college town. It’s green, laid back and friendly. You can walk or bike from the main campus to the main street in a few blocks. College students fill up the tables at nearby restaurants and coffee shops with their laptops, homework and friends. The town of Davis helps our students thrive. https://www.ucdavis.edu/

[4] Santorini (Greek: Σαντορίνη) is an island in the southern Aegean Sea, about 200 km southeast from the Greek mainland. It is the largest island of a small circular archipelago, which bears the same name and is the remnant of a caldera. It forms the southernmost member of the Cyclades group of islands, with an area of approximately 73 km2 and a 2011 census population of 15,550. The municipality of Santorini includes the inhabited islands of Santorini and Therasia, as well as the uninhabited islands of Nea Kameni, Palaia Kameni, Aspronisi and Christiana. The total land area is 90.623 km2. Santorini is part of the Thira regional unit.

[5] Casablanca, (Arabic: Dar al-Bayda; الدار البيضاء) is the largest city in Morocco and the country's economic and business centre. Located on the Atlantic coast of the Chaouia plain in the central-western part of Morocco, the city has a population of about 3.71 million in the urban area, and over 4.27 million in the Greater Casablanca, making it the most populous city in the Maghreb region, and the eighth-largest in the Arab world.

[6] Barium sulfate (or sulphate) is the inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odourless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and materials prepared from it. The white opaque appearance and its high density are exploited in its main applications.

[7] Titanium dioxide, also known as titanium(IV) oxide or titania, is the inorganic compound with the chemical formula TiO. When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It is a white solid that is insoluble in water, although mineral forms can appear black. As a pigment, it has a wide range of applications, including paint, sunscreen, and food colouring.

[8] Phoenix is the state capital and most populous city of the U.S. state of Arizona, with 1,608,139 residents as of 2020. It is the fifth-most populous city in the United States and the most populous state capital in the country.

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