This technical report presents the evidence that was used to develop and assess the UK Air Quality Plan for tackling nitrogen dioxide. It is important to note that whilst this national assessment describes one route to compliance with NO2 limit values it is unlikely to exactly reflect the eventual, locally developed plans. Supported by central guidance, local feasibility studies will use locally-specific modelling and knowledge to help design schemes which fit the local circumstances, and ongoing data collection will inform an adaptive approach that adjusts solutions as evidence emerges and uncertainty is reduced. The modelling in this report therefore provides a benchmark against which to assess local authority measures required by the Plan.