Many excellent points here. "Dirty" depends on where you drive and when you drive. I understand that NOx is mainly a problem in crowded, stagnant places like LA and big cities, in the summer when NOx reacts w/ hydrocarbons in the air to produce smog. Much HC comes from trees (think turpentine) and when I lived in Atlanta they actually speculated that cutting down pine trees to replace w/ hardwoods would decrease smog. Since the 1990's, we have had much more effective "3-way catalysts" that convert NOx in the catalytic converters so less EGR is needed, but I doubt that was even in the 1985 CA 300D converter.

Global climate change is a greater long-term concern and "net CO2" emissions is the main culprit. You can't burn any fossil fuel without emitting CO2, so the less burned the better (eat that SUV's and mega-trucks). Of course, this assumes climate change is man-made. I walk with my nose high because I now run my M-B diesels on the new renewable Diesel HPR, which is made from agricultural waste and thus releases no new CO2 like digging it up from the ground does.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans