New procedure for the calibration of mercury vapour concentration measurements in air
JRC scientists developed in collaboration with experts from the National Physical Laboratory (UK), the Netherland's National Metrology Institute and the Jozef Stefan Institute (Slovenia) a new measurement procedure for the calibration of mercury mass concentration at saturation in air samples.
As known for a long time, mercury is a very hazardous substance for human health and the environment. When released into the atmosphere, mercury can be carried over a long distance. European Union Directives 2008/50/EC and 2004/107/EC require that there is adequate information on concentrations of mercury in ambient air. However, European legislation does not provide target values for mercury in ambient air partly because there is not yet agreement on a procedure allowing SI (international system of units) traceable and sufficiently accurate calibrations of the mercury vapour measurement equipment. Calibration data most commonly used at present come from a fitting relationship to experimental results of measurements of mercury vapour concentrations in air obtained nearly 30 years ago. The way these results relate to the SI is not known. Furthermore there is a significant discrepancy (around 7% at room temperature) between these data and data based on results from mercury vapour pressure measurements, a concurrent approach.
The procedure developed by the JRC-Institute for Reference Materials and Measurements was based on measuring mercury concentrations in the vapour phase using isotope dilution in the liquid phase, and provided SI traceability at relative expanded uncertainty levels better than 5% (k=2). Results obtained under room temperature conditions seem to invalidate the reference data from 30 years ago and to confirm data from the concurrent approach.