Yale: ‘Asphalt pollutes the air more than cars driving on it’
On a hot summer day, the asphalt can pollute more than the cars driving on it. That is the surprising conclusion of American research, published recently in Science Advances. In the article, asphalt comes into the picture as one of the underexposed and not-inventoried causes of pollution.
Organic carbon compounds
The researchers of Yale University, among others, exposed fresh strips of asphalt to sunlight and increasing temperatures. Then they measured which substances the asphalt ‘breathed out’. Their analyses showed it was a considerable amount of (semi)-volatile organic carbon compounds. Substances you find in many other places, like in solvents of furniture or paint.
Some of those compounds in the air even pave the way for the creation of fine particles, the so-called secondary organic fine particles. They also contribute to the generation of ozone. Fine particles have a proven harmful effect on human health.
Warm summer day
The emissions of the examined asphalt were twice as high when temperature increased from 40 to 60 degrees Celsius. That’s the temperature of the road surface on a warm summer day. The UV rays, in their turn, made emissions triple. All this means that the emissions of asphalt are an outspoken summery phenomenon.
“To be clear: this has nothing to do with particles that are set free by the wear of the road surface,” emphasizes Drew Gentner of Yale University, one of the authors of the study in De Standaard.
Long-lasting source of pollution
The emissions are at the highest level when the asphalt is new, later they decrease gradually, but even then, the levels remain high, Gentner says. “At temperatures comparable to warm summer days, the emissions during our experiments continued for three days. That brings us to the conclusion that asphalt could be a long-lasting source of pollution.”
The researchers related their results with the air quality in the southern coastal region of California. A densely populated urban area that suffers from pollution and fine particles. They concluded that in the summer, asphalt emits more volatile organic compounds than gasoline and diesel engines from traffic.
Fortunately, the new generations of cars are getting cleaner and cleaner; even diesel engines are cleaner thanks to soot filters and catalysts. Their emissions will even go down in the coming years, while those of asphalt will probably go up, given global warming, the researchers predict. It will mainly be the case in urban regions where there’s more asphalt. So, they call to take this recently discovered polluter seriously.
“An interesting study,” confirms Frans Fierens, an air quality expert at the Flemish Environmental Society (Vlaamse Milieumaatschappij, VMM). “Until now, the emissions after production were hardly taken into account, but this study shows it would be worthwhile to review the matter,” the tells the newspaper.
Still, we should put things into perspective, Fierens says. “Traffic in Flanders represents 6% of all volatile organic carbon compounds. Is asphalt remains at the same level after production, then it’s clear we don’t have to overestimate the consequences. Those volatile carbon compounds are only part of the numerous polluting substances, like nitrogen oxide or particles.”