You must contact a workshop if you want to retrofit a diesel particulate filter to your van. Once the filter is fitted, it must be registered by an inspection centre. At the inspection centre, the filter is tested, and the inspection centre also ensures that the filter is registered in the Danish Register of Motor Vehicles (DMR).
There are no requirements for the type of particulate filter that must be fitted to a vehicle in order for it to meet the low emission zone requirements. Vans may get both open and closed particulate filters retrofitted.
Please, note that not all particulate filters are approved for all car models, which is why some vans may need to be retrofitted with a more expensive, closed particulate filter if they are to be used in the low emission zones.
Open particulate filters are cheaper than closed filters, but they do not filtrate equally efficient. If approved for your vehicle, open particulate filters can usually be ordered and installed by a mechanic, while closed particulate filters must be ordered from specialist particulate filter fitters and can be installed on the vast majority of vehicles.
The detailed rules for retrofitting particulate filters for vans are laid down in: