I found some more info on European emssions standards. It turns out that each norm actually has two sets of limits: The amount that a newly produced car can emit (Homologation Emissions Limit HEL) and the amount that the car can emit once in normal operation (Operational Emissions Limit OEL).
The following table shows HEL/OEL in grams per kilometer:
| Emissions norm | NMHC | THC | NOx | HC+NOx | CO | PM |
| EURO 3 petrol | --- | 0.2/0.4 | 0.15/0.6 | ---/--- | 2.3/3.2 | ---/--- |
| EURO 4 petrol | --- | 0.1/0.4 | 0.08/0.6 | ---/--- | 1.0/3.2 | ---/--- |
| EURO 5 petrol | 0.068/0.25 | 0.1/--- | 0.06/0.3 | ---/--- | 1.0/1.9 | 0.005/0.05 |
| EURO 5 petrol from 2013 | 0.068/0.25 | 0.1/--- | 0.06/0.3 | ---/--- | 1.0/1.9 | 0.0045/0.05* |
| EURO 3 diesel | --- | ---/--- | 0.5/1.2 | 0.56/--- | 0.64/--- | 0.05/0.18 |
| EURO 4 diesel | --- | ---/--- | 0.25/1.2 | 0.3/--- | 0.5/--- | 0.025/0.18 |
| EURO 5 diesel | ---/0.32 | ---/--- | 0.18/0.54 | 0.23/--- | 0.5/1.9 | 0.005/0.05 |
| EURO 5 diesel from 2013 | ---/0.32 | ---/--- | 0.18/0.54 | 0.23/--- | 0.5/1.9 | 0.0045/0.05 |
*) Petrol engines with direct fuel injection and part- or full-time lean burn
Legend: NMHC - Non-Methene Hydrocarbons
THC - Total Hydrocarbons
NOx - Nitrogen Oxides
CO - Carbon Monoxide
PM - Particulate Matter
Notice that EURO 3 and EURO 4 differ only in HEL, both have the same OEL. In other words, a EURO 4 vehicle may be just as dirty as a EURO 3, but the EURO 3 will have more restrictions in Germany's
Umweltzones, for example.
The new
EURO 6 standard, which will go into effect in September 2013 (type approval)/2014 (first registration) is still being revised, but two new limits for diesels are already known: NOx will be reduced from 180 to 80 g/km, and THC+NOx from 230 to 170 g/km.