[NTG-context] How to create a PDF/A file with mkii?

Dear List members, Does anyone know how to create a PDF/A file (where A stands for Archive) in mkii? In a thesis project which has to be uploaded on an archiving site it is required that the fonts should be imbedded into the PDF file and be compatible with the PDF/A standard. How can this be done without having access to a professional software from Adobe or other companies? Many thanks in advance: OK