Are Cooling Materials A Solution To Fight Urban Heat?

As temperatures climbed on a recent afternoon in Pacoima, a local park bustled. Kids splashed in the rec center pool and shot hoops on a basketball court. Adults relaxed in the shade of trees. A vendor sold ice cream.

Nine-year-old triplets Enam, Efemor and Eyako come to the park pretty much every day in the summer with their mom.

Efemor tried to catch a breeze on a playground swing.

"We saw it was 102, and to me that's pretty hot and doesn't make me want to do much," Efemor said.

Already in their short lives, Enam said they’ve noticed a change in the weather. 

"I feel like it gets pretty hotter, like kind of every year," she said. The last eight years have been the hottest on record globally, according to the World Meteorological Organization.

Ernestine Aglago and her 9-year-old triplets, from left to right: Eyako, Enam and Efemor Ladzekpo.

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Erin Stone

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LAist

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Cool pavement in one of L.A.'s hottest neighborhoods

Pacoima is one of the hottest neighborhoods in L.A. And the climate crisis is pushing average temperatures higher, and driving longer and hotter heat waves. All our buildings and pavement only make it worse.

Last year, grassroots group Pacoima Beautiful partnered with roofing company GAF to test how “cool pavement” might help. They painted 10 square blocks of streets, the park’s parking lot and basketball court, as well as an elementary schoolyard.

Cool pavement is among some types of materials that reflect solar radiation, instead of absorbing it. These coatings can also be used on rooftops and other surfaces exposed to the sun’s heat.

Eliot Wall, GAF’s cool pavement project director, pointed a thermometer at the ground.

"Here it's 132 degrees on this coated surface," he said.

We walk to an uncoated portion of the road. It’s 10 degrees hotter on regular old asphalt.

Why heat doesn't just go away

But cooler surface temperatures don’t automatically mean cooler communities, said V. Kelly Turner, a UCLA heat researcher.

"You can't make heat go away," Turner said. "You can only transfer that energy."

Her research found that cool pavement applied in L.A. may dramatically reduce surface temperatures, but can actually increase the air temperature just above the surface, where people are.

If the goal is cooler surface temperatures on a sidewalk so children or pets don't burn their feet as easily, a reflective coating might make sense. But if the goal is to reduce the heat load on people, planting trees or providing shade — from either trees or structures — could be more effective, Turner said.

"Shade cools surfaces as well and it also has a much larger effect on cooling the body," said Turner.

An aerial shot of the elementary schoolyard and street coated with cool paint.

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Courtesy of GAF

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Cool pavement is no silver bullet, but it’s relatively quick and cheap to apply and can have an immediate effect (GAF paid for the project in Pacoima). Wall said GAF's proprietary blend of acrylic-based rather than asphalt-based cool paint doesn’t have that same heating impact above the surface.

It's also been tested by the L.A. Bureau of Engineering for grip in wet weather and performs just as well as normal asphalt. And GAF designed it to be more durable than traditional asphalt coatings, according to the company.

GAF uses a modified electric golf cart to take all kinds of temperature readings, from surface to air to what's called mean radiant temperature, which is an ideal measurement for how humans will physically experience heat — and the main measurement used in Turner's study identifying heat load.

But preliminary research by GAF — that has yet to be confirmed by outside researchers — found the coatings helped cool the air temperatures for the 10-block area by three degrees during the record-long and hot heat wave in early September 2022.

"What we're seeing is the overall neighborhood effect that the air itself is cooler and that's even actually shifting with the wind downstream," said Wall.

GAF research found that during some of the hottest days, the area with cool paint was 3 degrees cooler than other areas, and wind even helped spread that cool air around.

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Courtesy of GAF

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What's next in Pacoima

Melanie Paola Torres, a community organizer with grassroots group Pacoima Beautiful, which leads the community engagement piece of the project, said community members are feeling a difference — and want more.

"We’ve seen things that do work, so we just keep hoping to add and stack onto that and really create a climate-resilient community," she said.

Back at the playground, the triplets and I carry out our own science experiment. (I did get their mother’s permission.)

The rubber underneath the swings and play structure measures at 172 degrees. Then we run over to the basketball court, bright with Dodger blue “cool paint.” Its surface is 40 degrees cooler.

Eyako sums up our findings.

"It used to be really hot like fire, and now it's like cooler and it's much more better for people to play basketball here," he said.

Still, cool coatings, though promising, require further research.