diesel can be very low emission, but not in the US
First off, Europe was way behind the US in getting rid of lead (a very good thing to get rid of) -- leaded gasoline is still common in Spain and Italy, for example.
Diesel engines with very low emissions, good fuel economy, and decent performance can be made, at least for cars -- the TDI (turbocharged diesel engines with, IIRC, pretty fancy fuel injection) do all three and are quite popular in Europe, even in luxury cars (e.g. BMW, Audi, Saab). But the only company to sell TDI cars in the US? VW.
The problem? US diesel fuel isn't high enough quality for TDI engines, and no one seems interested in increasing its quality.
So I expect that it would be possible to improve truck diesel emissions, too -- and I suspect doing this would do a lot more for air cleanliness than the current expensive ideas beloved by certain groups (such as electric cars and more mass transit funding).
Tony
