Annually produced 1x1km background concentrations from Department for Environment, Food and Rural Affairs (Defra) national Pollution Climate (PCM) models. These are typically (but not uniquely) annual mean concentrations. The download webpage shows the years available for each pollutant and provides additional information on the relevant units/metrics. The model results are used in conjunction with measured concentrations from Defra's national monitoring networks to provide an air quality assessment that is reported to the European Commission in accordance with European Directives. The methodology and results are described in a mapping report published by Defra on UKAIR website. Note that these background maps are distinct from the source sector split concentration maps produced for Local Air Quality Management (LAQM) purposes and should not be used for LAQM operations.