Locally worse, globally better
Diesel exhaust versus gasoline:
- about 15-20 % less CO2
- about 4-100 times the NOx (highly temperature dependent, mitigated by proper use of diesel exhaust fluid, ref the VW scandal)
- and a fair amount of soot (esp. before common rail, mitigated by a particle filter).
What this means for the local environment:
- Local CO2 is the least of problems, just good for the plants.
- NOx is the primary concern for lung illness in smoggy areas. It also creates acid rain, which (which can be a bit less local).
- People don't like to inhale soot either.
What this means for the global environment:
- Less CO2 = save the climate
- NOx breaks down methane, a strong greenhouse gas. So much so that ship emissions are estimated to have a net global cooling effect.
- Soot is probably not such a problem on the global scale yet.