A gravimetric approach to providing SI traceability for concentration measurement results of mercury vapor at ambient air levels

Abstract

Current measurement and calibration capabilities for mercury vapor in air are maintained at levels of 0.2–40 μg Hg m−3. In this work, a mercury vapor generator has been developed to establish metrological traceability to the international system of units (SI) for mercury vapor measurement results ≤15 ng Hg m−3, i.e. closer to realistic ambient air concentrations (1–2 ng Hg m−3) []. Innovations developed included a modified type of diffusion cell, a new measurement method to weigh the loss in (mercury) mass of these diffusion cells during use (ca. 6–8 μg mass difference between successive weighings), and a new housing for the diffusion cells to maximize flow characteristics and to minimize temperature variations and adsorption effects. The newly developed mercury vapor generator system was tested by using diffusion cells generating 0.8 and 16 ng Hg min−1. The results also show that the filter system, to produce mercury free air, is working properly. Furthermore, and most importantly, the system is producing a flow with a stable mercury vapor content. Some additional improvements are still required to allow the developed mercury vapor generator to produce SI traceable mercury vapor concentrations, based upon gravimetry, at much lower concentration levels and reduced measurement uncertainties than have been achieved previously. The challenges to be met are especially related to developing more robust diffusion cells and better mass measurement conditions. The developed mercury vapor generator will contribute to more reliable measurement results of mercury vapor at ambient and background air levels, and also to better safety standards and cost reductions in industrial processes, such as the liquefied natural gas field, where aluminum main cryogenic heat exchangers are used which are particularly prone to corrosion caused by mercury.

Comparability of calibration strategies for measuring mercury concentrations in gas emission sources and the atmosphere

“…The primary gas standard has been developed as an elemental mercury (Hg 0 ) gas generator to establish metrological traceability of mercury concentration measurement results, based upon a gravimetric approach, for ambient air levels as well as higher concentrations (Ent et al, 2014, de Krom et al, 2020 .…”

“…The agreement between these equations is unsatisfactory, with vapour pressures from different equations differing by more than 7 % at 20 ᵒC (Brow et al, 2010. To remove the dependency of mercury concentration measurements from these empirical equations, and to provide stability and comparability, a primary mercury gas standard has been developed by VSL (Van Swinden Laboratory, National Metrology Institute in the Netherlands), to provide metrological traceability to the International System of Units (SI) (Ent et al, 2014, de Krom et al, 2020. The SI-traceable primary standard, working according to ISO 6145-8 (ISO 6145-8, 2005), can be used for the calibration of instruments and the certification of mercury gas generators.…”

Validating an Evaporative Calibrator for Gaseous Oxidized Mercury

“…Recently, there has been progress in ensuring SI traceability of GEM calibrations. SI traceability was achieved by Ent et al [ 11 ], with a mercury vapor generator based upon an improved diffusion method that exploited gravimetric analysis to achieve traceability to the SI unit (mass) [ 11 ]. Živković et al [ 12 ] loaded iodinated activated carbon (AC) traps by reducing NIST SRM 3133 and by directly spiking the said SRM (Standard Reference Material ® ).…”

Comparability of calibration strategies for measuring mercury concentrations in gas emission sources and the atmosphere

“…The agreement between these equations is unsatisfactory, with vapour pressures from different equations differing by more than 7 % at 20 • C (Brow et al, 2010;Quétel et al, 2014). To remove the dependency of mercury concentration measurements from these empirical equations and to provide stability and comparability, a primary mercury gas standard has been developed by VSL (Van Swinden Laboratory, National Metrology Institute in the Netherlands) to provide metrological traceability to the International System of Units (SI) (Ent et al, 2014;de Krom et al, 2020). The SI-traceable primary gas standard, working according to ISO 6145-8 (2005), can be used for the calibration of instruments and the certification of mercury gas generators.…”

“…The trapping of mercury is usually performed with a sorbent tube using gold to form an amalgam and trap the mercury. To increase the surface area available, the gold is often dispersed on silica or a similar support (Brown et al, 2011(Brown et al, , 2017. Mercury in this adsorption tube is then thermally desorbed and measured.…”