Within the EMRP (European Metrology Research Programme) project “MeTra” a mercury vapour generator is being developed to establish SI traceability for mercury vapour measurement results in the range from 5 ng Hg/m3 up to 55 µg Hg/m3.
The novel calibration facility generates a tuneable mercury vapour directly traceable to primary mass standards. The facility can be used for the calibration of mercury monitors as well as for the loading of sorbent traps.
The facility consists of a modified type of diffusion tube, a new measurement method to weigh the loss in (mercury) mass of these diffusion tubes during use (with a minimum 6-8 μg mass difference between successive weighings), and a new housing for the diffusion tubes to optimize flow characteristics and to minimize temperature variations and adsorption effects.
The specifics of the newly introduced capabilities, to calibrate mercury monitors at levels of 5 ng Hg/m3 and higher, will be highlighted. This new calibration service is especially important for measurement services testing ambient air monitoring (1 – 2 ng Hg/m3), indoor and work place related mercury content levels according to health standards (from 50 ng Hg/m3) as well as mercury vapour concentrations relevant to stationary source emissions (upwards of 1 µg Hg/m3).