I posted this over at biodieselnow in response to the same article. I'm just pasting it here:
Some articles to read:
http://www.findarticles.com/cf_dls/m0CYH/17_7/109443861/p1/article.jhtml
(gasoline and CNG emissions contain as much (and as bad) PM or more than diesel vehicles with DPFs (diesel particulate filters)).
Our current VW TDIs do not have these DPFs (actually, the 2004s might, I'm not sure). They make a huge difference in the soot/PM output.
An excellent report to read is this one:
http://www.vv.se/publ_blank/bokhylla/miljo/2002_62/2002_62.pdf
It's a study done by the Swedish Road Transportation Agency, taking data for comparison between modern diesel and gasoline vehicles. They looked at both regulated and unregulated emissions. The diesel vehicles used were a VW Golf TDI without a DPF (so the kind we currently have over here), and one of the newer Peugot 307 diesels with common rail injection and a DPF, to see the impact of these new diesel technologies. They were compared to the gasoline versions of the same vehicles.
The paper linked is in both Swedish and English - they do a section in Swedish first, then English, so you'll have to skip over the Swedish sections (unless you know Swedish).
Neither of the diesel vehicles tested included NOx adsorbing catalysts, since those will only be included on new vehicles once ULSD is mandated (in 2006 in the US). So, the NOx emissions were of course higher on the diesels as expected.
But, the HC emissions were considerably lower on the diesels - by an order of magnitude or more. They did the testing at two ambient temperatures - 22C (roughly 70F) and -7C (roughly 20F). At 20F, the gasoline vehicles both emitted 20 times more HCs than their diesel counterparts. At 70F, the difference was only roughly a factor of 5 - but still far more HCs for the gasoline vehicles.
From a health standpoint, HC emissions are VERY important - they contain a lot of the possible carcinogens, plus are the most critical component in smog formation (which requires HC and NOx). The EPA is wrongly focusing on reducing NOx emissions, which will probably result in an increase in smog (since without HC emissions, NOx destroys smog. California is having a weekend smog issue that goes completely against the EPA's thinking. On the weekend, there is far less diesel traffic (no delivery trucks, etc.), so much lower NOx emissions, but roughly the same amount of HC emissions (which mostly come from the gasoline vehicles). If the EPA were right about reducing NOx resulting in a decrease in smog, then California should see lower smog levels on the weekend. In fact, it's the opposite. Smog is much worse on the weekends in Calfornia - due to the lack of an excess of NOx emissiosn which destroy smog.
Next, PM emissions. The diesel vehicle without the DPF (the Golf TDI) did have considerably higher PM emissions than the petrol version. But, the diesel vehicle WITH the DPF had LOWER PM emissions than either of the gasoline vehicles tested. The DPFs make that much of a difference. Yes, biodiesel reduces PM emissions around 30-80% or so, depending on the vehicle, but the DPF can reduce those emissions roughly 99%. The gasoline version of the Peugot emitted PM levels 10 times as high as the diesel version with the DPF!!
If you look at graph ES.5, which shows particulate emissions for the US06 cycle test and an overtaking test, the gasoline vehicles emitted roughly the same level of PM as the TDI without the DPF! The Peugot with the DPF was then around 3-4 orders of magnitude lower than either of the gasoline vehicles.
The gasoline vehicles showed a higher ozone forming potential (due to the much higher HC emissions), and higher HC emissions (than the DPF diesel). What this shows is that with the new diesel technologies coming to market, they are actually CLEANER than gasoline vehicles - even on the issue of particulate matter.
All of these graphs are on pages 20-23 of the pdf.
Yes, old diesel vehicles will still emit more soot, especially if they use petro diesel. But, the skies are getting clearer.