Oddly enough, that is also true :-)
What does it are traces of various ores in the soot. That stuff does not, however, circulate in the carbon cycle, nor is it spewn in the same amounts by cars.
The result is that all of the nice theory you hear about C14 dating doesn't really work for the last 50 years. (Insert opportunities for usual Creationist drivel.)
Cheers,
Ben
"... I couldn't see how anyone could be educated by this self-propagating system in which people pass exams, teach others to pass exams, but nobody knows anything."
--Richard Feynman