Sparks

White asphalt in the City of Angels

 By Luca Longo

This summer, as thermometers have reached highs of almost 40 °C, anyone who could, has fled the city for cooler climes out in the country…

You feel fresher the minute you get away from the sizzling concrete, the melting asphalt and the radiators in your neighbours’ air conditioners that pump out more hot air than a jumbo jet engine. In actual fact, climatology pioneer Luke Howard pointed out how much hotter the city is than the countryside as far back as 1818, in his essay “The Climate of London”. Based on yearly minute metereological observations, he demonstrated that the temperature in downtown was on average 2.1 °C warmer than the surrounding countryside. Howard also understood that it was mainly due to the responsability of human activity, because of the smog formed from chimney smoke and the presence of buildings. And this was before anyone had got around to inventing asphalt or air conditioning. Heat doesn’t just come from factories, boilers, transportation etc.; concrete, asphalt and bricks trap the sun’s rays and convert them into heat far more efficiently – more than a thousand times more efficiently, in fact – than earth, grass and trees.

L.A. gets fresher

The city of Los Angeles – which is on average 3.8 °C hotter than the countryside in summer and sometimes reaches peaks of over 40 °C – has had an original idea for making the summer a little less scorching for its 4 million inhabitants. The idea is to paint the roads white using CoolSeal, a water-based pigment that sticks to asphalt. It only takes two coats, each with a thickness of 50 microns, more or less the width of two human hairs, to turn the road white. When tarmac is changed from a dark colour to a light colour, it increases its albedo – a measure of how effectively it reflects the sun’s rays and sends them back into the atmosphere, rather than turning them into infra-red rays and therefore heat.

white-asphalt-reduce-heat-los-angeles
Laying the CoolSeal pigment on the streets of Los Angeles (GuardTop)

At 40,000 dollars for every mile of road, the costs are hardly negligible. However, the pigment is guaranteed to withstand traffic and the weather for at least seven years. Los Angeles residents have not only welcomed the new look of their roads, they’ve also tested first-hand that they can once again walk barefoot on roads covered in CoolSeal and that they can no longer fry an egg just by dropping it on the asphalt.

A model to emulate

Eric Garcetti, mayor of the Californian city, made the investment as part of a general programme to reduce greenhouse gas emissions in L.A. by 45% by 2025, returning to levels seen in 1990.
The initiative is addressed to citizens as didactical: the commitment and joint effort of businesses and local administrations, show that through our actions, climate change can be counteracted.
And in the City of Angels, the result is there for all to see!

about the author
Luca Longo