
VW and Mercedes have tinkered with particulate traps.  Also, VW
uses a kind of turbocharger on their Jetta ECOdiesel that helps
reduce particulates as well, although I don't know the
mechanics of it.

Many diesel cars,busses, and trucks in Europe are now being
equipped with catalysts and traps in an effort to clean up
diesel emissions, already well below legal limits anyway.

It's a shame GM had to soil the diesel's reputation in
passenger cars and prevent further resource devotion to
research into making this outstandingly efficient engine even
further ahead of gas engines in emissions.