US cities trial ‘sun block’ on asphalt to slash city heat and break down harmful traffic pollution

The ‘urban heat island’ effect can make daytime city temperatures up to 7F higher than rural areas

As the death toll mounts from last week’s deadly heat wave in North America, finding solutions to reduce life-threatening temperatures exacerbated by the climate crisis are increasingly urgent.

People who live in urban areas are especially at risk from extreme heat. Daytime city temperatures are typically 1-7F higher than in rural areas, and night-times can be 2F-5F hotter.

This is known as the “urban heat island” effect. High-rise buildings block air flow and cities are packed with asphalt roads, concrete sidewalks and metal roofs which re-emit more of the sun’s heat than in nature. On top of that, there’s “waste heat” from cars, air-conditioning, construction and industrial facilities.

The number of cities around the world exposed to extreme heat will nearly triple in the coming decades. By 2050 more than 970 cities will experience average summertime highs of 35C (95F). Today, only 354 cities are that hot, according to C40, a network of megacities committed to tackling the climate crisis.

Heat extremes can kill but also exacerbate illnesses like heart and lung disease, kidney problems, diabetes, and asthma. And excessive heat generally makes life more uncomfortable from breathing difficulties, heat cramps, heat exhaustion, and heat stroke. Young children, those with poor health and the elderly are most at risk.

As with the climate crisis overall, extreme heat disproportionately impacts the poorest and the disenfranchised. A study published last month found that Black Americans in most cities face twice the level of heat stress as white Americans.

One of the most lo-fi solutions to reduce urban heat is planting more trees which lower surface and air temperatures and provide shade. Greening cities with more parks, rooftop gardens and community vegetable patches also has an impact.

But there’s also high-tech innovations being rolled out to help urban-dwellers adapt to a hotter world.

One Cleveland-based company has a product which it says can not only cool baking asphalt but also break down vehicle tailpipe emissions which cause air pollution.

Pavement Technology, Inc has spent nearly a decade creating a titanium dioxide-based treatment, dubbed a “road rejuvenator.” (Its official name is A.R.A.-1 Ti but is known as Plus Ti).

Asphalt is the residue of distilled crude oil bound with coarser substances such as crushed rock, sand or gravel. Of America’s 2.6 million miles of paved roads, more than 94 per cent are surfaced with asphalt.

All asphalt has two molecular structures in common - maltenes which more or less “glues” the road together and asphaltenes which give the road its black colour and firmness. Over time, maltenes break down, causing the road to crack and become brittle. A.R.A.-1 Ti works by replacing maltenes to give asphalt back its original pep.

The company also dubs it a “smog-eater”. When titanium dioxide (TIO2) is hit with sunlight, an energy field buzzes atop the road, capturing and breaking down toxic tailpipe emissions like nitrogen oxides (NOx) and volatile organic compounds (VOCs) which make up smog.

Smog and other particulate matter from vehicles have been linked to heart and lung disease, heart attacks, worsening asthma and other respiratory issues.

The Plus Ti product is being piloted in the southern cities of Raleigh and Charlotte, North Carolina; Orlando, Florida, and Greenville and Charleston, South Carolina. It’s sprayed in a yellow coating from “Clean and Cool” trucks, and takes about 30 minutes to seep into the asphalt.

Ken Holton, technical consultant for Pavement Technology Inc, told The Independent that testing conducted in Charlotte and Raleigh has shown a more than 30 per cent reduction from tailpipe emissions.

And he noted that the sooner the product is sprayed on new roads, the greater the odds at extending its life span. A longer-lasting road means fewer carbon emissions emitted from manufacturing new asphalt or from heavy construction vehicles needed to make repairs.

But TIO2 comes with an additional benefit for hot cities - acting somewhat like a sun block by scattering warming radiation, cooling down the roads and reducing the heat island effect.

Pavement Technology Inc is also conducting research with Texas A&M University to see what impact TIO2 has on breaking down microplastics . Tire wear has been found to be a major source of these minuscule pieces of plastic, which end up in the ocean and enter the food chain.

Mr Holton says there has been increasing interest in A.R.A.-1 Ti from cities, particularly in the Southwest, where temperatures can soar into the triple digits.

“It's just kind of exciting,” he said. “We thought breaking down tailpipe emissions and cleaning the air for people to breathe was a big deal. And all of a sudden heat island [reduction] seems to be quite a big deal too.”