Primary mercury gas standard for the calibration of mercury measurements

Abstract

Mercury poses one of the greatest current direct threats to human, animal and environmental health across the globe. Robust, defensible and traceable measurements of mercury concentrations are essential to underpin global efforts to reduce the concentration of mercury in the environment, meet the obligations of legislation and to protect human health. Currently, instruments for gaseous mercury concentration measurements are calibrated based on mercury vapour pressure equations (e.g., the Dumarey or the Huber equation). Currently these equations differ from each other by more than 7% at 20 °C. In this paper, the performed characterisation and implementation of mercury diffusion cells and the development of the first primary mercury gas standard show that metrological traceability to the International System of Units (SI) is possible for mercury concentrations. The primary mercury gas standard will provide a lower measurement uncertainty (between 1.8% and 3%) than can be obtained using the most commonly adopted mercury vapour pressure equations (5% up to 21%). 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 the Dumarey equation. The developed primary mercury gas standard will contribute to more reliable mercury measurement results at emission and ambient air levels.