Tracking the "Secret" Life of Soot

Jul 24, 2013

Daniel Tkacik studies soot particles from vehicles in his temporary lab: the Fort Pitt Tunnel in Pittsburgh.
Credit Reid Frazier / Allegheny Front

Breathing in the tiny particles emitted by automobile engines and power plants has been widely accepted by scientists and the public as being something to avoid.

But for a long time it was believed that these tiny particles, known as soot, were the sole toxic ingredient entering the lungs.  However, Reid Frazier of the Allegheny Front has discovered quite a different story. Scientists have found that soot leads a “secret life” after being released into the air, during which it picks up gases and other poisonous hitchhikers.  Before the soot actually enters the lungs these particles go through a unique evolution that involves a surprising combination of molecules.

The atmosphere is comprised of roughly 20% oxygen and often these oxygen molecules form something called a hydroxl radical.

“This is basically a water molecule, that’s missing one hydrogen atom. So it’s really Jonesing for an extra hydrogen,” explains Harvey Jeffries, a retired chemist at the University of North Carolina who has studied these particles.

These hydrogen atoms can be found in everyday items like car exhaust and spray can fumes, and when the hydroxl radical finds these hydrogen atoms it wants to condense.  Typically this combination, a secondary organic aerosol, chooses to attach itself to air particles such as soot. These gooey-like substances float around in the atmosphere and eventually end up in our lungs. Frazier explains that it is not necessarily the soot that carries toxicity, but the “dirty” atmosphere.