| Carol,
  While it has been a long time since I've seen the list off emission
constituents put out by Diesel engines, I do recall that while they are
higher in particulate emissions - the black soot you referred to when
they are accelerating - they emit fewer noxious emissions on the whole
than gasoline burners.  
  Someone remarked about aircraft engines.  On the whole it's easier to
clean up a gasoline-burning aircraft engine than it is to clean up a car
engine.  The reason is that aircraft engines run at a steady RPM and
load most of the time, while a car engine spends most of its time
accelerating and decelerating in city traffic.  Same for jet engines AND
they burn JP-4, a high grade kerosene, which is more like Diesel fuel
than it is like gasoline.  All these things make a difference as to
emission types and amounts.
  Now, before anyone starts flaming me, I invite you to read up on it
and prove me wrong with facts, not engage in hyperbole.
  Charley Robinson
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