What happens to all the rubber that wears off of tires?

Dear Car Talk

Dear Car Talk | Sep 01, 1999

Dear Tom and Ray:

This question is so simple that you've probably been asked it a million times.
What happens to all the rubber that wears off of our tires? You never see it, but
it's got to be somewhere. -- Mike

RAY: That's a very good question, Mike. And we didn't know the answer. So we went
to the high priests of automotive/scientific knowledge, the Society of Automotive
Engineers. You know what? They thought it was a very good question, too. And they
didn't know the answer.

TOM: So then we asked the Rubber Division of the American Chemical Society. They
also thought it was a very good question. And, you guessed it, they didn't know
the answer either.

RAY: While none of these lofty scientific organizations actually KNEW the answer,
they all had theories, of course! And the universal consensus among all of these
esteemed scientists is that the "rubbed-off-rubber" is entirely broken down by
the sun and air. It's broken down into its molecular parts -- carbon, nitrogen
and some sulfur.

TOM: That stuff is then blown into the air and exists as "suspended particles."
That's scientific notation for "dust." Obviously, the carbon and sulfur
contribute somewhat to airborne pollution, but how much, and whether the amount
is at all significant, we don't know.

RAY: This theory was arrived at by process of elimination. There have been people
over the years who have suggested that the rubber doesn't break down, but instead
builds up indefinitely by the side of the road. But if that were the case,
according to Bill Whoerle, tire expert at the SAE, "We'd be plowing rubber
instead of snow."

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