Thomas Smith is a Higher Research Scientist in the Emissions and Atmospheric Metrology group at the National Physical Laboratory. His research has focused on understanding uncertainty in emission measurements made using EN14181 and related standards. Other research areas include ambient particulate monitoring and greenhouse gas inventories, in particular city-scale emission quantification and reporting.
The EU requires measurement and reporting of emissions from medium and large combustion facilities under the Medium Combustion Plant Directive (MCPD) and the Industrial Emissions Directive (IED). In most cases these emissions need to be measured continuously by automated measurement systems (AMS) that have passed type requirements according to EN15267. The quality control framework for the AMS is laid out in EN14181, including periodic calibration by parallel running with a reference method. The IED sets out measurement uncertainty limits but assumes if an AMS passes the testing in EN14181 it will meet the uncertainty requirements. To investigate if this was true a Monte-Carlo model was created to simulate a gas analyser operating under EN14181. The initial results were presented at CEM 2016 and demonstrated that in most situations EN14181 did keep the AMS within the limits required by the IED, although there were scenarios tested that resulted in significant levels of uncertainty in the annual mass emissions.
That model focussed on concentration and modelling the AMS and processes in EN14181. Since then the model has been extended as part of two EMPIR projects, SulfNorm and IMPRESS2. SulfNorm was focussed on emissions of SO2, for which the standard reference method (SRM) is a wet chemical test rather than an instrumental technique. The uncertainties associated with performing the reference method, described in EN14791, were integrated into the model to test the impact of falling emission limit values (ELV). The uncertainty requirements in the IED are a percentage of the ELV, so as limit values are lowered it becomes more difficult to meet them. The model demonstrated that further reductions in the SO2 ELV could leave the SRM unable to meet the uncertainty requirements, so action is required to address this. The IMPRESS2 project looked at issues faced in smaller plants covered by the MCPD, particularly related to flow measurement according to EN16911. Plants report annual mass emissions, requiring a combination of measured concentration and volume flow rates. Flow rate varies with proximity to duct walls, so measuring in the narrower ducts at smaller plants presents a significant measurement challenge. Flow measurement in the model was extended to determine if measurement uncertainties in such plants can still meet the reporting requirements.