Odense is one of the cities that has a low emission zone. Within the low emission zone, diesel-powered lorries, buses, vans and cars must comply with special requirements for particle emissions. The zone is limited by Ring 2 and all approach roads are clearly signposted that you are entering or leaving the low emission zone.

You can see a map of the low emission zone here

Here you can see what you need to fulfil in order to enter the low emission zone in a diesel car - rules for vehicles in the low emission zone