It is possible to have a particulate filter retrofitted if your vehicle is affected by the regulations for driving in low emission zones.

The specific regulations for retrofitting particulate filters for vans are laid down in  

Executive Order no. 1059 of 22/10/2019 on requirements for diesel-powered lorries, buses and vans in municipally determined low emission zones, etc.   

Executive Order 1474 of 21/12/2009 on exemption from particulate emission charges by retrofitting particulate filters. 

The specific regulations for retrofitting particulate filters for lorries and buses are determined in

Executive Order no. 1059 of 22/10/2019 on requirements for diesel-powered lorries, buses and vans in municipally determined low emission zones, etc.   c.f. § 8 the fitting of an effective particulate filter must be supported by a signed declaration by the filter supplier, c.f. appendix 1.

Before the declaration is presented at the vehicle inspection facility, the declaration must be emailed to the Danish Environmental Protection Agency at miljozoner@mst.dk. The Danish Environmental Protection Agency will then assign an identification number, which the owner or user must affix to the declaration.