That 40X number journalists love to quote

No media story related to VW's situation fails to mention a 40X increase in emissions, usually without specifying it as NOX, thereby implying it includes CO2 as well (which cannot be true if mpg is above the sticker numbers, which it generally is.) As I see the UWV data, the 40X refers to hill climbing, i.e., "worst case". This is not to downplay VW's problem. In the UWV data, I see that the Jetta emitted 7X times the BMW level going up hill. That's not 40X but it's still pretty bad.

Since all vehicles use more fuel going up hill, typically 2-3 times as much, surely all vehicles (gasoline diesel and even hybrid) must emit more than the "allowable", whatever that is.

Does this make sense?

Yes, and that's a good point!

An Environment Canada paper published around the same time as the ICCT/WVU report shows that during the cold-start phase of the FTP test duty cycle, gasoline engines emit up to 40 times the regulatory limit of PM under some "real-world" conditions (0 degrees F ambient temp in this case), and that's BOTH GDI and PFI (http://pubs.acs.org/doi/abs/10.1021/es501791b).

Black carbon (BC) was measured at 57 to 162 mg/mile (0.057 - 0.162 grams/mile) from four gasoline vehicles (2 PFI and 2 GDI) under those conditions. According to EPA, BC accounts for about 20% of PM emissions in gassers, except about 40% during starts. For the worst of those vehicles (PFI), 162/0.4 = 405 mg/mile (0.405 grams/mile). Regulated limit is 0.01 grams/mile (Tier 2), so that vehicle is emitting more than 40 times the regulated limit during the first ~10 minutes of the FTP after a cold start.

GDI has also been shown to produce high particulate number emissions at start (cold or hot), up to 8000 times more than a diesel with DPF under the same conditions (http://papers.sae.org/2015-01-1077/). This is an issue especially for GDI with start/stop systems. This paper was presented at an EPA conference in RTP, NC, earlier this year.

There's also no mention of the generally well-below-certified levels of all of the other regulated emissions (HC, CO, and PM) in the ICCT/WVU report in any press releases that I've seen.

It just doesn't sound a juicy to say 40x on NOx but only 1/10th on all other emissions. Leave it to the media to blow all sense of reality or common sense out the window. All vehicle exceed the limits at some point in the duty cycle. That is why there are averaging formulas for overall test results.

Here is a comparison of the emissions of the 2013 Passat as reported in the ICCT/WVU report and the average gasoline car on the road in 2008...


2013 Passat TDI emissions in ICCT/WVU report ("multi-state" test) vs. average gasoline vehicle fleet emissions in 2008 per EPA

(Grams/mile)

Emission...................Average Gasser in 2008*........................Passat TDI In-Use**

THC..................................1.077..................................................0.01
NOx..................................0.693..................................................0.42
CO....................................9.400..................................................0.03
PM....................................0.0044................................................0.0002


*EPA, "Average Annual Emissions and Fuel Consumption for Gasoline-Fueled Passenger Cars and Light Trucks" http://www3.epa.gov/otaq/consumer/420f08024.pdf (Page 4)

**2013 Passat in-use emissions - Thompson et al., "In-Use Emissions Testing of Light-Duty Diesel Vehicles in the United States." International Council on Clean Transportation Report, May 15, 2014 (Pages 77-86)

To be fair, NOx is the greatest smog forming constituent, so that's what I'd care about most anyway. I've already got air conditioning, so CO2 is not of much concern to me.

So, what I'm seeing is that, even at a TDI's worst, it's nowhere near as bad as a gas engine. What are we whining about again?

Yes, it's obvious to me that, even with the current level of NOx emissions, TDis should have a place in the overall vehicle fleet, given their low levels of other contaminants. A balanced US fleet would consist of TDis, efficient gas cars, electrics, and hybrids.

InfoSec Guy said:

So, what I'm seeing is that, even at a TDI's worst, it's nowhere near as bad as a gas engine. What are we whining about again?

Click to expand...

Those numbers are for the entire US gasoline fleet (including older vehicles that are both wearing out and didn't have as stringent emissions requirements to begin with) as it stood 5 years prior to the emissions requirements for the 2013 Passat, the more accurate comparison should be between MY2013 gas vehicles only.

"These emission factors and fuel consumption rates are averages for the entire in-use fleet
as of July 2008. Newer vehicles generally emit less pollution and use less gasoline, while older
vehicles generally emit more pollution and use more gasoline. This is due to several factors,
including the increasing stringency of emission standards over time and the deterioration (degradation)
in the performance of emission control technology (e.g., catalytic converters) with
increasing age and accumulated mileage"

Agree that a more recent set of emission factors would be more useful. Hopefully EPA will update those emission factors soon. It would also have been useful if a modern gasoline vehicle was included in that WVU real-world test.

Nevertheless, except for NOx, all other regulated emissions in the WVU test are still much lower than certified levels, never mind regulated levels....


2013 Passat TDI


(Grams/mile)

Emission..................Certified (FTP)..........................In-Use ("multi-state" - "urban")

NMOG...........................0.036........................................0.000032*
NOx..............................0.03..........................................0.840
CO................................0.2...........................................0.013
PM................................0.002........................................0.00002

THC was reported at ~0.007 grams/km or ~0.01 grams/mile; 95%-98% of THC was CH4 (methane) which is not counted as NMOG (NM = "non-methane") (Page 67 of ICCT/WVU report)


2013 Passat certified emissions - http://www.arb.ca.gov/msprog/onroad/cert/pcldtmdv/2013/volkswagen_pc_a0070311_2d0_u2_diesel.pdf

CraziFuzzy said:

To be fair, NOx is the greatest smog forming constituent, so that's what I'd care about most anyway. I've already got air conditioning, so CO2 is not of much concern to me.

Click to expand...

Is NOx actually the greatest smog forming constituent in the grand scheme of things?? Maybe wxman could comment. Also note that NOx isn't anything you can see or smell.

I'd like to learn more about the weekend ozone effect observed in Los Angeles and a few other urban areas where smog levels have been observed to INCREASE on the weekends compared to during the week. Note that weekends are when there is about 90% less diesel truck traffic on the roads. I don't think the higher smog levels on weekends are due to everyone mowing their lawns because the effect has been noted especially in tunnels.

If all on-road diesel vehicles suddenly disappeared tomorrow, we would then have the weekend ozone effect 7 days a week. IMHO, I think the EPA's and CARB's over-obsession with NOx is misguided.

For what it's worth, here are the default gasoline and diesel passenger car emissions used in the GREET model...

The ozone ("smog") issue was discussed recently in another thread here (http://forums.tdiclub.com/showthread.php?p=4946610#post4946610).

Apparently, ozone levels in Chicago have not gone down in spite of reductions of ambient NOx levels (http://www.luc.edu/media/lucedu/sus...e of Ground Level Ozone to Climate Change.pdf).

n1das said:

Is NOx actually the greatest smog forming constituent in the grand scheme of things?? Maybe wxman could comment. Also note that NOx isn't anything you can see or smell.
I'd like to learn more about the weekend ozone effect observed in Los Angeles and a few other urban areas where smog levels have been observed to INCREASE on the weekends compared to during the week. Note that weekends are when there is about 90% less diesel truck traffic on the roads. I don't think the higher smog levels on weekends are due to everyone mowing their lawns because the effect has been noted especially in tunnels.
If all on-road diesel vehicles suddenly disappeared tomorrow, we would then have the weekend ozone effect 7 days a week. IMHO, I think the EPA's and CARB's over-obsession with NOx is misguided.

Click to expand...

I should have clarified that NOx is the greatest smog forming constituent that is generated by motor vehicles. Many chemicals lead to smog production in the atmosphere: NOx, ozone, PAN, VOC's, etc - but NOx is the one that comes primarily from combustion. It is also why the introduction of 3-way catalytic converters made such a huge impact on smog levels in urban areas in the 80s, as they significantly reduced NOx emissions. It got even better in the 90's after the acid rain legislations put SCR's on major power plants and refineries, reducing NOx even more.