Two sets of standards have been defined for light-duty vehicles in the Clean Air Act Amendments (CAAA) of 1990:
Tier 1 standards applied to all new light-duty vehicles (LDV), such as passenger cars, light-duty trucks, sport utility vehicles (SUV), minivans and pick-up trucks.
First 50k miles/5 years all in g/mi
NOx Diesel 1.0 - More relaxed NOx limits for diesels applicable to vehicles through 2003 model year
NOx gasoline 0.4
PM 0.08 - PM standards applicable to diesel vehicles only
And those are...
THC - Total hydrocarbons
NMHC - Non-methane hydrocarbons
CO - Carbon monoxide
NO - Nitrogen oxides
PM - Diesel particulate matter
Well let's look at a Golf 5door TDI S
Estimated fuel consumptions;
EC Urban (mpg) 49.6
EC Extra Urban (mpg) 74.3
EC Combined (mpg) 62.8
So i'm not entirely sure the arguement that it would fail emission laws holds up.