Sunny Days Cause Air Pollution to Release from Streets

asphalt emits hazardous chemical compounds throughout summer, experiments show

By Jonny Lupsha, Wondrium Staff Writer

Yale researchers have discovered heat causes air pollution to rise from asphalt, EurekAlert reported Wednesday. They tested chemical compound emissions from asphalt at different temperatures and amounts of solar radiation to come to their conclusion. Asphalt is popular for paving roads partly because it’s highly recyclable.

Sunset on road
During an experiment with fresh asphalt, researchers found that heating it to summer-like temperatures caused a release of organic compounds into the air, which contribute to air pollution. Photo By Grisha Bruev / Shutterstock

According to EurekAlert, which is published by the American Association for the Advancement of Sciences, asphalt roads and roofing are a bigger problem for the environment than previously thought. “A new study finds that asphalt is a significant source of air pollutants in urban areas, especially on hot and sunny days,” the article said.

“Yale researchers observed that common road and roofing asphalts produced complex mixtures of organic compounds, including hazardous pollutants, in a range of typical temperature and solar conditions. Because of the type of compounds asphalt emits, its potential [secondary organic aerosol] formation is comparable to motor vehicle emissions in Los Angeles.”

Asphalt is a popular choice for roads and roofing alike. This is because it’s made from leftovers of crude oil and is highly recyclable.

What Is Asphalt?

Asphalt concrete is the single most recycled petroleum product. Where does it come from?

“Although some asphalt occurs naturally, like at the La Brea Tar Pits in Los Angeles, most of it comes from crude oil,” said Dr. David W. Ball, Professor of Chemistry at Cleveland State University in Ohio. “It’s the last part of the petroleum, the leftovers after all of the other volatile components, or fractions, have been removed. Technically, asphalt is the fraction that boils over 500 degrees Celsius, which is 930 degrees Fahrenheit.”

Dr. Ball said that asphalt is also known as bitumen and pitch. While it’s used for waterproofing and making roofing shingles, its most popular use is as part of asphalt concrete for roads. Asphalt concrete is also known as pavement, blacktop, and tarmac. This mixture is only about 5% asphalt and 95% gravel, sand, and crushed stone.

“Heated to several hundred degrees, the asphalt coats the stones in a thick, gooey black layer, which can be spread onto the ground like icing on a cake,” Dr. Ball said. “As it cools down, it hardens into a solid road, driveway, or airport runway. Of the 2.6 million miles of paved roadways in the United States, it’s estimated that 93% of them are covered with asphalt concrete.”

Reduce, Reuse, Re-Pave

Anyone who’s spent enough time driving knows the difference between a brand-new paved road and an old one. The appearance, the quality, and even the feel of the road under your tires are different.

“Over time, [roads] crack under the sun; get exposed to rain, and snow, and ice; and have tons of cars and trucks running over them,” Dr. Ball said. “They get cracks, potholes, and generally start breaking apart. These roads need to be repaired, so the asphalt concrete is removed and—guess what—recycled, sometimes even on the spot.”

According to Dr. Ball, the old asphalt concrete can be scraped up, heated, mixed with new asphalt, and relaid. In fact, he said that it’s estimated that only one percent of asphalt ever actually gets thrown away in landfills because it’s so recyclable. Asphalt roofing shingles aren’t so lucky.

“Most shingles are actually composite materials of fiberglass or paper coated with asphalt, and there’s no good way to separate the asphalt from the other materials after they’re manufactured,” he said. “There are some efforts underway to develop recycling procedures for asphalt shingles, but older shingles may be contaminated with asbestos, which complicates any recycling process. Right now, most asphalt shingles are disposed of in landfills.”

Edited by Angela Shoemaker, Wondrium Daily

Dr. Ball is a Professor of Chemistry at Cleveland State University in Ohio.

Dr. David W. Ball contributed to this article. Dr. Ball is a Professor of Chemistry at Cleveland State University in Ohio. He received his bachelor’s degree from Baylor University and his master’s and doctoral degrees from Rice University.