Flow Uncertainty and Impact on Annualised Mass Emissions The aims of this work package are to determine the uncertainties and provide traceability of mass emission measurements related to flow calibrations carried out in field conditions. This will be done through the determination of traceable flow measurement uncertainties propagated for annualised mass emission reporting (Task 3.1), the investigation of the uncertainty contributions of wall effects and sensor obstructions in small ducts and pipes (Task 3.2) and the investigation and validation of novel flow monitoring technologies and the use of multiple sensors in stack flow measurements (Task 3.3). The activities defined in this work package will involve modelling and laboratory as well as field measurements. Another important activity in this work package is the integration of the flow measurements into the annualised reporting of emissions, and the estimate of the associated uncertainty budgets. Task 3.1: Traceable uncertainties of flow measurements propagated for annualised mass emission reporting under real field conditions The aim of this task is to evaluate the uncertainties of flow measurements propagated for annualised mass emission reporting under real field conditions and provide a traceability scheme. Evaluation of uncertainty sources and review of various published ad-hoc studies, for instance L-type versus S-type uncertainty sources on annualised mass emissions will be performed. In addition, in this task, further refinement of a previously developed model to allow account to be made of calibration of the in-situ flow monitor against different portable techniques will be conducted. Task 3.2: Impact of wall effects and sensor obstruction in pipes and ducts The aim of this task is to evaluate the errors and added uncertainties in flow-rate measurements due to non-ideal flow conditions in pipes and ducts. The disturbances of the flow near the wall and sensor obstructions will be assessed. Task 3.3: Investigation of flow monitoring technologies and the use of multiple sensors in stacks The aim of this task is to investigate errors and uncertainties in flow-rate measurements due to geometrical obstructions and flow disturbances in the stack. For instance, influence of a bend at a supplying pipe to a stack on Pitot tube measurements will be investigated. A laboratory test protocol for investigating the influence of upstream disturbances on the flow monitoring devices for stacks will be formulated.