TURNING BLACKTOP GRAY is an innovative means of reducing the effects of climate change in Phoenix, the nation’s fifth largest city (news to me) and hottest (familiar from my visits, even in April). Here are tidbits on this gleaned from cbsnews.com, July 22, 2022, and other sources.
Background. Phoenix is known for its clear skies and sunny days; indeed, to extremes. I recall enjoying the Phoenix Art Museum’s annual Copperstate 1000 Rally. It’s traditionally held in April, though even at that time of year sagacious Phoenicians know the trick of positioning themselves in whatever shade is available.
TV weather reports have annual guessing games with Phoenix residents predicting the first day of official triple-digit temperature. Yes, it’s typically “dry heat,” with really low humidity, but triple digits are, count them, triple digits.
According to CBS News, “Phoenix recorded its hottest summer ever in 2020, with 50 days at or above 110 degrees and a record 28 nights when the temperature never dropped below 90 degrees.”
Asphalt, aka Blacktop. A typical asphalt road surface is blackish in color and, thus, readily absorbs the sun’s heat. In fact, the most recent Formula 1 race, at France’s Paul Richard Circuit, displayed this. Autoweek, July 21, 2022, predicted, “… it is set to be a hot one, with ambient temperatures in the mid-90s, and track temperature potentially nudging 140º F.”
According to Arizona State University News, September 21, 2021, “Summer’s heat and sun can push the surface temperature of city streets in Phoenix as high as 180 degrees Fahrenheit. Those streets then stay hot long after the sun goes down, radiating their built-up energy back into the night air, making the next morning hotter, in an ongoing cycle.”
“If you’ve ever owned a black vehicle,” the ASU article continued, “you know it gets hotter than a white or silver vehicle when parked in the sun. Scientists at the Lawrence Berkeley National Laboratory found that difference between dark and light-colored vehicles can be 10 degrees Fahrenheit or more.
“The same is true for the pavement we drive on,” ASU wrote. “Lighter, more reflective surfaces will stay cooler than darker ones. But could that difference be enough to make an entire neighborhood cooler and more comfortable?”
Yes to CoolSeal Solar Gray. ASU reported, “Roadway engineers with the city of Phoenix put a team of Arizona State University researchers to work to answer that question. A yearlong joint study by the city and ASU applied a reflective gray treatment called CoolSeal to 36 miles of neighborhood roads and a parking lot. After months of measurements, sometimes on days as hot as 116 F, the team has some answers: Surface temperatures of the roads with the reflective CoolSeal layer stayed cooler than non-treated streets at all times of the day; as much as 10 to 12 degrees cooler at noon, and almost two and a half degrees cooler at sunrise.”
Recent Results. CBS reports that “About 73 miles of the city’s streets are now covered with sealant.” Phoenix Mayor Kate Gallego tells CBS, “Our residents say they can feel the difference.”
It’s More Than Just Comfort. “Here in Phoenix, the number of people who die from homicides every year is about on par with the number of people who die from heat,” David Hondula, director of heat response and mitigation, told CBS News. “Heat is killing about 300 people per year in Phoenix.”
“This is a problem that’s only going to get worse, so we need to do better,” Hondula said. “We need to do more and we need to be doing it fast.”
“The city is creating 100 cool corridors,” CBS says, “planting hundreds of trees whose shade can drop the ambient air temperature by about 30 to 40 degrees compared to full sun. Phoenix is also experimenting with reflective roofs and cooling sidewalks.”
CBS observes, “Cities are warming at twice the global average because buildings and pavement absorb and trap so much heat. Phoenix, Los Angeles and Miami have named chief heat officers to find ways to prevent the often deadly impacts of extreme heat.”
And solar gray asphalt is one means of mitigating this. ds
© Dennis Simanaitis, SimanaitisSays.com, 2022