Defra is seeking to contract with supplier(s) possessing the scientific, technical and analytical expertise required to maintain and develop the UK National Focal Centre (NFC). The successful supplier(s) will deliver annual UK-wide modelling and mapping of pollutant deposition (ammonia, oxides of nitrogen and sulphur dioxide) and assess against critical loads for acidity and nitrogen. They will also map ammonia concentrations and assess against critical levels. The assessments will be reported for the UK as a whole and broken down by country. In addition, the data will be reported for specific habitat types, Special Areas for Conservation (SACs), Special Protection Areas (SPAs) and Areas/Sites of Special Scientific Interest (A/SSSIs). The modelled outputs will support annual reporting, evidence generation, biodiversity protection, environmental policy development and the UK´s domestic and international reporting obligations. We are envisaging that the new contract will start on the 01 June 27 with a one (1) month handover, from 01 June to 30 June, with full responsibility being transferred to the successful contractor on 01 July 2027. These handover periods are to allow the new Contractor time to get ready to take over the full operation of the contract requirement. We estimate the contract value to be between the range of £680,000 - £720,000.