The fact is that diesel is cleaner than gasoline in almost all aspects.
Especially in important greenhouse gas emissions.
Yes, given the horrendously low quality diesel sold in the US until this
year, diesel did have higher NOx and particulate emissions in _some_
configurations and conditions, but not all. However this will change
with the newly mandated low-sulphur diesel.

Looking at actual data from fueleconomy.gov you find the following:

Volkswagen Jetta, 2006

Engine				MPG Cty/hwy		Yearly greenhouse 

                                                         gas emissions/tons

1.9L Diesel			36/41			5.6 tons

2L Premium Gas			25/31			6.7 tons

2.5L 5cyl reg gas		22/30			7.4 tons

Chevrolet Suburban
5.3L gas			15/20			10.6 tons
5.3L E85			11/15			8.6 tons
6L Gas				14/18			11.3 tons
Honda

Accord Hybrid

Hybrid/reg gas			25/34			6.6 tons

Mercedes E320CDI

3.2L Diesel			27/37			7.0 tons

Lincoln Town Car

4.6L reg gas			17/25			9.3 tons

Ford F150

Pick-up 5.4L gas		14/18			12.0 tons


You can see that diesels do far better than gasoline engines in fuel
economy and in greenhouse gas emissions.
The former disadvantage in particulate emissions will be reduced or
eliminated by the new low-sulphur diesel and by increased use of bio-diesel.


Steve Ravet wrote:
>> Now that refineries in the U.S. have been forced to lower the 
>> sulfur content -- diesel is a nice way to go.
>>     
>
> Diesel is bad news for air in the US.  Europe may have diesels that are
> as clean as gas but over here they are all, Mercedes included, really
> dirty.  The EPA OTAQ WWW page has an excel spreadsheet with every single
> model.  The jetta is worse than a 3/4 ton Suburban.  Low sulphur diesel
> may allow for better emissions control equipment, but it alone doesn't
> make a diesel engine cleaner.
>
>   
What is the basis of your Jetta vs Suburban statement?

The EPA ratings are based on mostly effect on human health, not on
environmental impact. Certainly this is important, but also can be
misleading when trying to compare technologies. It's a lucky coincidence
that the more directly harmful emissions to humans are also the easiest
to deal with. For example particulates. These can be simply trapped. 
Mercedes has already made huge strides with Blue-tec on NOx and
particulates. Greenhouse gases are more complex, and more difficult to
deal with.

>   
>> The Nissan Titan wallops the current older-generation U.S. 
>> trucks for quality, fit-and-finish, and various other things 
>> -- while still maintaining a good price point -- but where's 
>> the diesel version?  I need to TOW heavy things, and I don't 
>> want to lower my fuel economy to drop to about 8-10 MPG to do it.
>>     
>
> I don't think the Japanese make anything but a half ton pickup, do they?
>
> --steve
>   
At present diesel is at least as clean as gasoline, and provides greater
fuel-economy. However diesel technology has more room to grow. It's
potential has yet to be maximized. Also, it's cheaper to produce than
gasoline, and has higher yields from crops for bio-fuels than Ethanol.
Not to mention Ethanol produces a lot less energy per acre than biodiesel.

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