ARS SCIENTIA : Something in the Air

A stand-up comedian somewhere has surely built a routine around the mystery of what happens to the rubber from your tires as they wear out. You can almost hear the Seinfeld-like whine: “Where does it all go?” The answer: Into the air, our eyes, our lungs.

Caltech recently completed a major study of just what goes into L.A.-area smog and found that some of it comes from tire dust and minibits and pieces of all kinds of other junk.

The survey, part of a comprehensive examination begun 12 years ago, focused on fine particulate matter, specks that are less than two micrometers in diameter. Fine particulates, which make up a third of all smog, are the chief component of visible pollution. Because they are readily inhaled deep into lungs, they are believed by many researchers to be a significant health threat.

Joining tires in contributing to fine particulate pollution: jets, roofing tar pots, brake linings, cigarettes, forest fires, fireplaces, road dust and meat-cooking operations.


A frequent question, says the study’s director, Glen R. Cass, professor of environmental and mechanical engineering at Caltech, is why his team focused on something that is but a small part of the total smog problem. “Well, we know exactly what we’re doing. You have to examine the aggregate to find out that, collectively, the minor sources add up.”

Cass and his colleagues employed several innovative methods to isolate all these micropollutants. To target cigarette smoke, for example, they traced molecular markers found in the surface waxes of tobacco leaves.

Now, if they could just find a tracer for all those toxic gasses emanating from radio talk show hosts.