Exactly Tom on many points...
Exactly Tom on many points...
Diesel fuel is no worse smelling than gasoline; it's just that most Americans are more used to smelling nasty gasoline than nasty diesel. The only thing that may make diesel slightly worse is that it does not evaporate, but that's a positive thing as it relates to pollution...
NOx has nothing to do with black smoke or soot, the latter has been totally eliminated from modern diesels. NOx is a class of gasses created by lean combustion. Gas engines don't create them, because they run rich by comparison and must do so in order that gasoline ignites via a spark. NOx is not a harmful substance like soot. NOx is a precursor to smog and in order for smog to be created by NOx it has to combine with other man-made compounds in the air like VOCs. VOCs come from plastics; from the tailpipes of gas cars; and from manufacturing processes. Back in the late 90s, the EPA and the California ARB conspired on a plan to make the trucking industry pay for reducing smog by cracking down on NOx from diesel exhaust; thereby keeping it easy on the auto industry and from manufacturing for reducing smog. This is how we ended up with limits on NOx down to near nothing for light-duty vehicles and it's also how we ended up with very expensive and very complicated and complex and sophisticated diesel engines under the hoods of everything diesel.
The modern, soot-free diesel engine can be designed to be at least as powerful as a naturally-aspired gas engine of equal displacement nowadays. Those that think otherwise are thinking of the "good ole days". The limits on NOx that are only applied in North America puts slight limits on their performance and limits how marketable they are here, because it makes them so hard to build and so expensive to certify for 50-state emissions.
Modern diesel engines are amazing. Almost everything about the technologies have surpassed that of spark-ignition except that power and torque are not quite as linear. But if you think about it, horsepower is the enemy of fuel economy. The more work you can get out of an engine at the lowest possible horsepower being generated, the less fuel you're going to burn everything else being equal; so if a torquey little diesel is moving a pickup and its load at 70 mph and generating only 90 horsepower; it's going to get better mpg than an equally-displaced gas engine doing the same thing generating 130 horsepower.