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Environment

Yale study finds dangerous emissions from asphalt long after it's laid

By Loz Blain
September 04, 2020
Yale study finds dangerous emissions from asphalt long after it's laid
The hotter it gets, the more urban emissions you get from hot asphalt, according to a new Yale study
The hotter it gets, the more urban emissions you get from hot asphalt, according to a new Yale study
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The hotter it gets, the more urban emissions you get from hot asphalt, according to a new Yale study
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The hotter it gets, the more urban emissions you get from hot asphalt, according to a new Yale study

The more we work to get emissions down from motor vehicles and power generation, the more we'll have to start looking at non-combustion sources of emissions – and a new Yale study suggests that asphalt, so ubiquitous in our modern cities, continues to release a wide range of chemicals into the air long after it's laid down – and it's three times worse on hot days.

The world as a whole uses around 122.5 million metric tons of asphalt a year, and this sticky, black, semi-solid form of petroleum, also known as bitumen, is a key component in roads, pavements and roof sealing. There are significant and well understood emissions at every stage of the production and laying processes, and a Yale team has found that asphalt continues to release "complex mixtures of organic compounds, including hazardous pollutants" even as it's just sitting there.

The asphalt industry "states that emissions at ambient temperatures are negligible," according to the Yale team, "because the manufacturing process removes all potential emissions." But the team has found that what's really happening is that these compounds simply diffuse slowly through the highly viscous asphalt.

As any motorcyclist knows, a hot day can soften bitumen to the degree where a sidestand can push right through. The same softening, says the Yale team, can speed up these emissions leaks by up to 300 percent, as evidenced by a lab study looking at a range of different temperatures and conditions.

The result: another as-yet-ignored source or urban "secondary organic aerosol," or SOA, production, contributing to the amount of PM2.5 (a regulated air pollutant comprising particles smaller than 2.5 micrometers across) in the air. PM2.5 pollution is recognized as a significant public health issue, and the researchers estimated the SOA released from sitting asphalt across the Los Angeles area to be comparable to that emitted from vehicles in the same area.

The researchers note this is not a CO2 or ozone issue, and that asphalt is "just one piece of the puzzle" – but there's an awful lot of it out there, and finding ways to make roads more environmentally friendly as well as the vehicles that drive on them is looking like another important challenge for the future.

The study is available at Science Advances.

Source: Yale

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7 comments
Loz Blain
Loz Blain
Loz leads the New Atlas team as Editorial Director, after nearly two decades as one of our most versatile writers. He's also proven himself as a photographer, videographer, presenter, producer and podcast engineer. A graduate in Psychology, former business analyst and touring musician, he's covered just about everything for New Atlas, concentrating lately on clean energy, AI, humanoid robotics, next-gen aircraft, and the odd bit of music, motorcycles and automotive.

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7 comments
Brian M
Unfortunately just about everything we do has a 'bad' effect' even if we do nothing then nature creates its own bad effects. We have had multiple mass extinctions through time without any helping hand from us! Think volcanic eruptions, meteorites etc etc.

Perhaps just need to concentrate on the things that have really bad consequences such as global warming - Even global warming is not really that bad in terms of the planet surviving, its been there, done that and got the T shirt. We might not just be around to see it (roaring cheer heard from the rest of the plant and animal kingdom!).

guzmanchinky
I've always hated the smell of asphalt, gives me an instant headache and I always felt awful for the people who had to work to make roads with it.
paul314
Ironically, people may get more exposure to these emissions on bikes than in a nicely sealed car.
moreover
In Europe there's a push for using permeable pavers instead of asphalt on parking lots. Their main benefit is superior drainage. Avoiding harmful emissions makes permeable pavers an even better proposition.
Pablo
Ok, let’s switch to concrete... oh, that’s right, manufacturing that’s a rather dirty process, too! How about we all move to sod huts, go barefoot and survive off the land? That would also have a profound effect on the environment to say nothing of the vast acreage we’d need. We’re a bit dirty, but also entitled to live on the planet. Almost everything any organism does will disrupt some other... we’re just exceptionally good at it!
vince
That's one good reason why putting solar panels above the roadways makes a lot of sense--the shading will lower the bitumen evaporation substantially with the sun blocked out. It will make for longer lasting roads that don't form potholes as frequently as the rain and snow will also be lowered that hit the surface and the lowered cracks in the surface due to the shading means less cracks for water to flow into and ICE to crack open the cracks into potholes. Solar covered roadways are a win win for the environment.
ljaques
Every surface has its downside. Permeable pavers are made with concrete, so you have its footprint.