Asphalt is used to surface more than 95% of all UK roads as well as footpaths, playgrounds, cycle ways and car parks

On hot sunny days, the surface of footpaths, roads, and playgrounds becomes a significant source of air pollution, scientists from Yale University have discovered.

Asphalt is used to surface more than 95 per cent of all UK roads as well as footpaths, playgrounds, cycle ways and car parks, according to the UK’s Asphalt Industry Alliance.

But evidence published in the journal Science Advances suggests that road and roofing asphalt emits hazardous pollutants – particularly during the summer months – which is driving urban air pollution across the country.

Hot, sunny days are worst

The Yale study collected fresh asphalt and heated it to between 40°C and 200°C. The hot asphalt emitted a “substantial and diverse mixtures of organic compounds” small enough to be breathed deep into human lungs, the team said.

The emissions level varied dramatically with temperature. Emissions doubled when the temperature increased from 40°C to 60°C, the temperature asphalt can hit during a hot summer.

Sunshine also had a dramatic impact. When the scientists exposed road asphalt to solar radiation, emissions jumped 300 per cent. “That’s important from the perspective of air quality, especially in hot, sunny summertime conditions,” said lead author Peeyush Khare.

Emissions were highest when the asphalt was fresh, but after about a week stabilised at a significant level, the scientists said.

The team now suspect asphalt is a significant contributor to air pollution in cities during the summer months. During LA’s summer, asphalt could produce more particulate emissions than petrol and diesel vehicles combined, they suggested.

EVs won’t solve the problem of air pollution

The findings will add to the growing body of evidence suggesting a switch to electric cars won’t completely solve the problem of urban air pollution. Earlier this year researchers from the University of Cambridge confirmed that brake dust is a major source of air pollution, and could be as bad as diesel in terms of its health impacts.

Climate change will make these problems worse. Like many other nations, the UK is already experiencing longer, hotter summers and meteorologists expect this trend to accelerate as greenhouse gas emissions continue to rise. The Yale team warned the rising temperatures will mean asphalt pollution is likely to increase in the coming years.

Asphalt found to be driving air pollution in urban areas on hot sunny days