Just how dirty is dirty?
I can't even begin to keep up with this thread, so I apologize if what I write has already been said (multiple times) before.
To the question of just how dirty is the TDI? The WVU/ICCT real world driving study that helped promulgate all this tested just 3 vehicles: 2012 Jetta with NOx trap, 2013 Passat with urea SCR and BMW X5 with urea SCR. It found all three vehicles well below EPA threshold for all metrics except NOx. It found them better than European standards for PM (particulate matter). It found that the X5 was below NOx limits in all driving tests except "uphill/downhill rural driving." It found the 2013 urea SCR Passat was often below NOx thresholds, particularly on flat roads and cruise control highway driving. On the test drive between San Diego and Seattle, it was below NOx thresholds 50% of the trip and on average exceeded EPA standards by 6 fold. This is actually pretty amazing performance. The study's stated purpose wasn't to bust VW but to demonstrate discrepancies between real world and test performance, something the ICCT had already demonstrated for 13 different manufacturers across gas and diesel for efficiency related metrics. Why should they be the same? The dyno tests are simply 10 minutes of attenuating the speed on weighted rollers. They don't account for hills, headwind, driver variability... all factors demonstrated by the study to affect emissions performance. Some factors you hope are invariant since the emissions controls are catching them, some aren't (like CO2). If you step on the gas uphill, there's more environmental stress, clearly.
Okay, not to excuse VW's performance (corporate or vehicle), but: the Passat's NOx output between SD and Seattle averaged 0.415g/mile with a huge standard deviation (btw: I love mixing metric with US unit miles). For comparison, in 2013 California was estimating the state's fleet of light duty vehicles was putting out 0.213g/mile NOx in real world conditions (3 fold greater than the EPA threshold of 0.07g/mile for new vehicles). That estimate is likely too low though. In 2008, the EPA estimated the real world passenger fleet average was 0.693g/mile. That's probably gone down by now. (These are numbers I found on the agencies' websites respectively). So, how did the 2012 urea SCR VW do? A bit worse than average for CA. Considerably better than average for the national average. And, of course, considerably worse than average against what it was supposed (EPA) to or was advertised as. I haven't seen any evidence that many of the effected models won't pass CA smog testing without the defeat device. If the tests change (as is the recommendation), that's a different story.
Regulators seem to face a bit of a dilemma with regard to fixes. The NOx fixes (like changing how lean the engine runs) could drive down NOx emissions while increasing other pollutants. So which pollutants do you care about more? Even in fairly strict California, NOx is considered more of an urban problem (smog, not to belittle acid rain in rural areas). About half the state is even considered NOx exempt where commercial operators can apply for exception if their vehicles are staying within area (ex. buses and logging trucks). The idea (right or wrong) is that the NOx breaks down before doing any damage. As for the VWs, vehicles like the 2009 are probably beginning to be retired anyway. It's not clear to me that any drastic fix make environmental sense.
Ditching vehicles is insane (ex. lemon laws). A huge part of a vehicle's footprint is from manufacture (estimates often state around 50%). Once they're out there, they have to be pretty dirty before it makes sense to obsolete them for something new. I'm happily keeping my 2015, not to say I'm not a bit disappointed with the news.
Aaron in Berkeley, CA
