"Primary mercury gas standard for the calibration of mercury measurements" (Measurement)
The paper describes the performed characterisation of mercury diffusion cells and primary mercury gas standard. The development of the first primary mercury gas standard shows that metrological traceability to the international standards (SI-units) is possible for mercury concentrations with a lower measurement uncertainty than can be obtained using the most commonly adopted mercury vapour equations. Measurement methods have been developed for the SI traceable calibration of mercury analysers and mercury gas generators which have been used for the comparison between the primary mercury gas standard and current calibration facilities.
“Comparability of calibration strategies for measuring mercury concentration in gas emission sources and the atmosphere” (Atmospheric Measurement Techniques)
This paper demonstrates the robustness and comparability of the novel primary mercury gas standard, the results of comparisons are presented with current calibration methods maintained at different institutes, using the bell-jar in combination with the Dumarey equation or NIST liquid standard reference material. The results show that the primary standard and the NIST reference material are comparable, whereas a difference of -8 % exists between results traceable to the primary standard and the Dumarey equation.
In extension to the comparisons highlighted in the AMT article, future intercomparisons between the VSL primary mercury gas standard and the NIST (National Institute of Standards and Technology in the United States) primary measurement method based on Laser Absorption Spectroscopy are planned.
At the moment metrological traceability for mercury measurements is established at the national metrology institutes. There is no standardized procedure that ensures dissemination of the developed metrological traceability in calibration and testing laboratories and in the field. 1st of October 2020 the “19NRM03 SI-Hg” (Metrology for traceable protocols for elemental and oxidised mercury concentrations) project started. SI-Hg is a three-year project (2020-2023) funded under the European Metrology Programme for Innovation and Research (EMPIR) as a part of Euramet (www.si-hg.eu). The goal of the project is the production of metrological traceable protocols for the certification of elemental and oxidized mercury gas generators. Scientifically sound certification protocols in the form of formally accepted documentary standards, are of fundamental importance to guarantee the accuracy and comparability of the mercury measurement results. The certification protocols contribute to establishing a traceability chain from a primary mercury gas standard to measurement data obtained in gas emission sources and in the atmosphere in Europe and globally. Standardisation committee CENTC264/WG8 has already formulated a new work item on the certification protocol to transform the protocols developed in the project into European standards.
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