Similarly particle filters, catalytic converters and whatnot reduce efficiency via exhaust backpressure.
So all in all, reducing non-CO2 emissions do come at a cost in CO2 emissions (or fuel consumed, if you like). Is it as much as 15%? No idea.. And is it all worth it? I'd argue yes, old-school diesel exhaust is nasty stuff.
As for your later point...I very much concur. I started masking (n95) during the pandemic, and haven't stopped. I have a... large number of health issues including several respiratory ones. Exhaust in general really is nasty stuff. I live in pretty quiet smallish (100k) town, and it can be bad enough around here with all the pollen, but I wasnt recently on a whirlwind trip through the north east that saw me visit the dense urban cores of DC, Philly, Manhattan, and Boston. The difference in odor on the occasions I'd take my mask off on the sidewalk were kinda shocking as someone not used to it.
Not sure what you're arguing here. Isn't it quite obvious that resistance in the exhaust system means that the engine has to do more work to push the exhaust gases out; work that otherwise could be used to turn the crankshaft. Now of course a lot of that extra energy is wasted in any case, particularly if there's nothing like a turbocharger to make use of it.
Backpressure aft of the turbo is something you really want to avoid because it makes the turbine much less effective. The whole point is to use a pressure and thermal gradient to do work.
Something about the large, hardly noticeable depression traps bad air at a regional level. I wouldn’t move back for a myriad of reasons, but everyone is always surprised when I list air quality as one.
Coming from NWI, I know the mills had a lot to do with subpar air quality, but I had similar issues when I lived on the far Northside of Chicago so it seems to be more regionally affecting.
It's a similar top reason on my list to not living there long term again
Here is a quick overview of how the system works.
Currently only smaller engines are EGR+DPF only. It takes having an SCR(&DEF) system to reduce emissions to legal limits on most larger engines now and the technology has been combined to have an engine with EGR+DPF&SCR(&DEF).
There are issues with engines and the active regeneration that has to occur in order to clean the DPF(basically engine has to get very hot and burn out the buildup) and also issues with DEF, which is an ammonia solution, both with the electronic dosing units failing and solution purity.