

Diesels fall into the same emissions mythology as alcohol fuels.  The main reason
they are considered "cleaner" is because they are better at the emissions we
actually measure and regulate.  But they also contribute additional emissions
which have long been determined to be as harmful, but no suitable control or
limits have been defined.  

Current evidence is pointing to most visible smog actually being diesel emissions
and suspended particles and less of a photo-chemical reaction.  Diesel particulates
are now becoming a major concern in decreased lung capacity.  And alcohols emit
signifcantly more aldehydes (a known carcinigen) than gasoline.  The evidence
is mounting that while we have been beating the gasoline engine to death, we may
have been ignoring the effects of the alternatives.

And anyone who thinks diesels are so great, should go and spend a few hours in
rush hour traffic in some cities in Europe.  There the stench of the diesels is
awful and it can even burn the eyes.  

Diesels being clean is only relative to our current standards. 