April 30, 2020 The preliminary results of CCQM-K74.2018 10 µmol mol-1 NO2 in nitrogen were discussed in two virtual web meetings during April. The preliminary results highlighted the challenges of preparing NO2 reference materials. Outputs from the MetNO2 project are helping to understand how to determine the most appropriate key comparison reference value that will be used to determine the degree of equivalence between the participants.