CPV code 90731210 designates Purchase of CO2 emission credits in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
90731210 is a leaf code — the most specific level of its branch — so it can be used directly as the main CPV code of a contract notice. If it does not quite fit, check the neighbouring codes under 90731200 (Transboundary air pollution management or control services).