Just for further information, let's see how tiny pollutant output is vs. CO2.
So, the TDIs after the fix have a slightly changed target for NOx output. Instead of supposed to emitting only 0.07 g/mi of only NOx, they're supposed to emit no more than 0.15 g/mi of NOx and NMOGs combined where previously, NMOGs and NOx were regulated individually.
Combine that with the outputs of other pollutants wxman listed and the total amount of pollutants per mile is less than 0.2 g/mi of ALL pollutants... Let that sink in. ALL regulated pollutants COMBINED, less than 0.2 g/mi.
Now, let's just say after the fix, someone is averaging 38 MPG.
To calculate how many grams per mile of CO2 output that is, let's first take what the EPA says a gallon diesel will emit when burned, which is 10,180 grams.
In order to put into perspective pollution numbers as measured by CARB and EPA in grams per mile, let's find out the grams per mile CO2.
Easy enough, take 10,180 and divide it by your miles per gallon (38 in my example above).
10,180 / 38 = ~267.9 g/mi CO2.
Now, let's take about what the cheating cars were averaging as far as NOx and other combined pollutants. They were measuring an average right around 1.2 g/mi NOx from what I've read. And the rest of the regulated pollutants COMBINED for just shy of 0.041 g/mi.
Now, the EPA also said that after the fix the gen 1 engines were going to lose upto 2 MPG. Some report far larger losses, some right around that number, some are a little less than 2 MPG loss. But, let's just assume that 2 MPG loss was accurate.
So, let's add 2 to the 38 above (since I stated the 38 MPG was what someone might average post-fix). 40 MPG. Let's figure out what that is in terms of g/mi CO2.
10,180 / 40 = 254.5 g/mi CO2. A difference of 13.4 g/mi CO2.
So, in order to reduce pollution near 1 g/mi, the gen 1 engines now output around 13.4 g/mi extra CO2. Add that up over a lifetime...
One could realistically argue that with how much cleaner these cars are in every other regulated form of emissions, relaxing their NOx targets a little isn't a bad thing, especially if that means you can gain some efficiency if you believe that the minimal impact of local air quality from the small change in NOx output vs. encouraging the adoption of any and every form of transportation that emits less CO2 thanks to its efficiency, one could certainly make the argument that the tradeoff is worth it, depending on where you place your priorities as far as local U.S. air quality vs climate change concerns.
Especially once one sees and experiences for themselves that the areas with the worst air quality in the U.S. are also dependent on what the weather is doing. L.A. in particular has had more and more hot, sunny and stagnant or offshore wind days that compounds air quality issues, and if one is to believe that excess CO2 output is contributing to warming of the planet which is affecting areas like L.A. and they're experience even more of the weather patterns that create bad smog days, and less of the windy, rainy days that help clear things up then you can see where some of us rationalize that anything that helps reduce CO2 output is a good thing, even if that comes at the expense of a small increase in NOx.
Besides, there's always "the weekend effect" study that was done in L.A.. where they noted an uptick in bad air quality on weekends, which are the days which there is much less diesel truck traffic and thus less NOx. That's because in those hot, sunny and stagnant weather conditions, NOx interacts with VOCs in the local air to create more smog, and there's a specific ratio of those two pollutants that when reached, actually maximizes the production of smog. And it just so happened to be that when that study was done, reducing NOx output got the ratio of NOx to VOCs closer to optimal to maximize production of smog. For the record, gas engines emit far more VOCs than diesels, and the refueling process alone emits quite a lot of VOCs with gasoline, which is why California has these vapor recovery boots on their gas pumps (but not diesel, because diesel doesn't turn to vapor at normal ambient temperatures. No evaporative emissions equipment at all on diesel vehicles. No charcoal canister, leak detection pump, purge valve etc).
However, other studies claim that if NOx can be reduced down to near nothing, the air quality will noticeably improve. The one I can think of was done here in the Bay Area in the Caldecott Tunnels. But, during the transition period to vehicles that produce near zero levels of NOx, there will be an increase in bad smog days because the ratio of NOx to VOCs will be closer to optimal, as noted in the previous weekend effect study mentioned above...
SO, there you go. The L.A. basin is being doubly screwed currently by not only having increased number of hot and sunny, stagnant weather days due to climate change but also because the transition to exceptionally low NOx output vehicles is making the local air closer to the optimal ratio of VOCs to NOx to make smog worse... at least for now. The idea being that once older diesels are cycled out of use, the extra low NOx emissions of the newer generation vehicles will change things for the better... eventually.
So, for those of us who've been following emissions issues for some time are a little hesitant to believe that the rapid ramp down of NOx was the right way to go about it, especially when you talk to technicians and fleet owners who've had nothing but increased downtime and headaches due to reliability issues of the new smog equipment. Not that they should never be implemented, but that they maybe needed more time to develop and mature before being strictly required. That and combined with the above observations that a reduction in NOx does not always make for a reduction in smog and that bad smog days are also related to what the weather is doing. And when you put into perspective how many pollutants per mile vs. CO2 output, you could be excused for putting a larger emphasis on the CO2 ouptut since there's a couple hundred times more CO2 coming out of your tailpipe than pollutants...