Work package 1 High Accuracy Static Primary Reference Standards Develop traceable NO2 reference standards with unprecedented levels of uncertainty and stability with fully characterized impurities Develop novel methods to supress impurity formation Work package 2 Dynamic methods for calibration of low amount fractions and dissemination to monitoring stations Develop high accuracy traceable dynamic standards of NO2 at low concentrations. Demonstrate improved accuracy and comparability of direct NO2 measurements at monitoring stations. Work package 3 Spectroscopic measurements of nitrogen dioxide and impurity analysis Develop methods to quantify main impurities in NO2 reference standards. Validate NO2 selective spectroscopic methods and compare in the SAPHIR atmospheric simulation chamber at the World Calibration Centre for NOx. Work package 4 Creating Impact Rapid dissemination of new reference standards and measurement guidelines through direct involvement of representatives of key atmospheric monitoring communities. Well coordinated with existing members of ACTRIS II and IAGOS communities » contribute to efforts to improve reliability and traceability of NO2 measurements in Europe. Knowledge transfer to support direct NO2 market (instrument manufacturers and speciality gas industry.) Work package 5 Management and Coordination The consortium combines high quality and relevant expertise from the NMI/DI community with that of the atmospheric monitoring community. NPL is well experienced in managing large research projects and has a dedicated project management team that will play a key role in enabling a successful project.