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Braking Bad

Two researchers standing outside with the city in the background

Hongyu Guo, Georgia Tech graduate student, and Rodney Weber, a professor in Georgia Tech’s School of Earth and Atmospheric Sciences

By Josh Brown

Though tailpipe emissions could fall in the years ahead as more zero-emission vehicles hit the streets, one major source of highway air pollution shows no signs of abating: brake and tire dust.

Metals from brakes and other automotive systems are emitted into the air as fine particles, lingering over busy roadways. Now, Georgia Tech researchers have shown how that cloud of tiny metal particles could wreak havoc on respiratory health.

In a study published in the journal Environmental Science & Technology, the researchers described how vehicle-emitted metals such as copper, iron, and manganese interact with acidic sulfate-rich particles already in the air to produce a toxic aerosol.

“There’s a chain reaction happening in the air above busy highways,” said Rodney Weber, a professor in Georgia Tech’s School of Earth and Atmospheric Sciences. “Acidic sulfate in the atmosphere comes into contact with those metals emitted from traffic and changes their solubility, making them more likely to cause oxidative stress when inhaled.”

The study, which was sponsored by the National Science Foundation and the U.S. Environmental Protection Agency, showed how the metals are emitted mainly in an insoluble form but slowly become soluble after mixing with the sulfate.

“Sulfate has long been associated with adverse health impacts,” said Athanasios Nenes, a professor and Georgia Power Scholar in the School of Earth and Atmospheric Sciences and the School of Chemical and Biomolecular Engineering. “The old hypothesis was that the acidic sulfate burns your lung lining, which in turn leads to bad health effects. But there is not enough acid in the air alone to really have that impact.”

The researchers analyzed samples of ambient particulate matter at two locations in Atlanta — one near a major interstate highway and the other at an urban site 420 meters away from a roadway.

Related: Brake Dust May Cause More Problems Than Blackened Wheel Covers, March 2, 2017

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