Euro emissions standard and green sticker: Wrong numbers on the environmental sticker?

A diesel with the Euro 5 standard – and still the "4" on the sticker instead of the "5"? If you're asking this question, you're not alone. The different numbers on the environmental sticker and in the Euro emissions standard are always confusing. There's a good reason why the two regulations refer to different numbers. The number on the sticker represents something completely different than the emissions standard that manufacturers and buyers list in brochures and registration documents.

The colored stickers on the windshield are part of the environmental zone concept in German cities. Their purpose is simple: They are intended to show at a glance whether a vehicle meets the respective environmental regulations. But what irritates many is that the number on the sticker does not refer to the Euro emissions standard , but rather to the so-called pollutant group .

The higher the emissions group, the lower the vehicle's particulate matter emissions – and the greater the likelihood of being permitted to enter environmental zones. The scale ranges from 1 to 4. Vehicles in emissions group 1 – usually old diesel or gasoline vehicles without a regulated catalytic converter – do not receive a sticker at all. Group 2 is red, Group 3 is yellow – and only Group 4 earns the green sticker. This sticker is currently required for entry into all environmental zones.

This is where things get technical—and political. The European emissions standards regulate limits for various pollutants , including nitrogen oxides (NOₓ), carbon monoxide (CO), and particulate matter. However, for the classification into the pollutant groups indicated by the sticker, only particulate matter emissions are relevant, especially for diesel engines.

The Federal Environment Agency (UBA) explains: "The lower the average particulate matter emissions, the higher the pollutant group." This is the number on the environmental sticker. "Vehicles with modern exhaust aftertreatment receive pollutant group 4."

In concrete terms, this means that a Euro 5 diesel engine , which emits relatively high levels of particulate matter, can end up in the same emissions category as a Euro 4 gasoline engine , which operates significantly more cleanly. The emissions standard alone is not sufficient to assess a vehicle's environmental impact—especially when different drive systems come into play.

Retrofit solutions also play a role. Vehicles with retrofitted particulate filters do not automatically meet a new Euro standard, but are assigned to a higher emissions group based on their reduced particulate mass . This means that even Euro 3 diesels with filters can slip into Group 4 and thus receive the green sticker. This is another reason why the number on the sticker does not correlate with the Euro standard.

Instead of basing the number of stickers on the Euro standard, the allocation is based on the so-called emissions code in the vehicle documents. This code can be found in Part I of the registration certificate under item 14.1 , or in older vehicles under code number 1 .

These codes can be used to determine the particulate matter emission level – the basis for legally regulated classification into the correct pollutant group. The basis for this is Appendix 2 of the 35th Federal Immission Control Ordinance (BImSchV) .

The ADAC has published a helpful overview that lets you find out which emission code belongs to which pollutant group in just a few clicks. Those who want to see for themselves will find practical tables and classification aids there.

On German roads, low-emission zones are not about emissions standards, but solely about the visible sticker. Police and regulatory authorities only check the presence and color or number of stickers —either in moving traffic or on stationary vehicles in parking areas.

The UBA clarifies: "The authorities do not monitor the emissions standard, but rather the resulting particulate matter emission level, represented by the pollutant group." This also makes it clear: Whether a vehicle complies with Euro 5 or Euro 6 is irrelevant for the inspection – what matters is whether it has the correct sticker . Currently, all environmental zones in Germany require the green sticker , i.e., pollutant group 4.

That would make sense at first glance, right? After all, you often know which Euro standard your car meets—for example, Euro 4 or Euro 5. But that's exactly what would be confusing. Why? A gasoline car with Euro 5 emits much less particulate matter than a diesel with Euro 5. If both cars simply had "Euro 5" on the sticker, it would look as if they were equally environmentally friendly —but they aren't.

Some older diesel vehicles have been later fitted with a soot filter to reduce particulate matter emissions. The car then receives a better environmental sticker, but the Euro standard doesn't change – it remains at Euro 3 or Euro 4. So, if the emissions standard were listed on the sticker, the conversion wouldn't be noticeable . The Federal Environment Agency shares this opinion: Simply listing the Euro standard on the sticker doesn't reliably indicate how clean the car actually is.