That's an interesting article. It seems like they didn't consider the soot's ability to block sunlight when it's suspended in the air. That might compensate for some of the reduction in sunlight reflectance of snow. What I find ironic is the Bush administration's anti-diesel stance while at the same time they're shielding gas-guzzling SUV's and pickups from tougher fuel economy standards, and rejecting the Kyoto protocol.
But the article is only talking about limiting heavy-duty diesel emissions, and I'm all for that. Light-duty diesels like our cars are not that bad.