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

Abstract

Abstract. A primary mercury gas standard was developed at Van Swinden Laboratory (VSL) to establish an International System of Units (SI)-traceable reference point for mercury concentrations at emission and background levels in the atmosphere. The majority of mercury concentration measurements are currently made traceable to the empirically determined vapour pressure of mercury. The primary mercury gas standard can be used for the accurate and precise calibration of analytical systems used for measuring mercury concentrations in air. It has been especially developed to support measurements related to ambient air monitoring (1–2 ng m−3), indoor and workplace-related mercury concentration levels according to health standards (from 50 ng m−3 upwards) as well as stationary source emissions (from 1 µg m−3 upwards). The primary mercury gas standard is based on diffusion according to ISO 6154-8. Calibration gas mixtures are obtained by combining calibrated mass flows of nitrogen and air through a generator holding diffusion cells containing elemental mercury. In this paper, we present the results of comparisons between the primary gas standard and mercury calibration methods maintained by NPL (National Physical Laboratory in the United Kingdom), a National Metrology Institute (NMI), and the Jozef Stefan Institute (JSI), a Designated Institute (DI). The calibration methods currently used at NPL and JSI are based on the bell-jar calibration apparatus in combination with the Dumarey equation or a NIST (National Institute of Standards and Technology in the United States) reference material. For the comparisons, mercury was sampled on sorbent traps to obtain transfer standards with levels between 2 and 1000 ng with an expanded uncertainty not exceeding 3 % (k=2). The comparisons performed show that the results for the primary gas standard and the NIST reference material are comparable, whereas a difference of −8 % exists between results traceable to the primary gas standard and the Dumarey equation.

Traceable Calibration of Atmospheric Oxidized Mercury Measurements

“…Routine field calibrations of Hg 0 are needed that are independent, SI-traceable, and occur in ambient air at the inlet tip. Manual syringe injections are sometimes carried out at the inlet tip, but these are based on saturated Hg vapor equations that have discrepancies and are not SI-traceable. ,− The methods presented here can be used for routine Hg 0 calibrations in addition to Hg II .…”

Atomic spectrometry update – a review of advances in environmental analysis

“…Standards could be prepared with a relative expanded uncertainty of 3% ( k = 2) for concentrations between 0.1 and 2.1 μg m −3 and 1.8% for concentrations between 5 and 100 μg m −3 . The so-called “bell-jar” calibration, which involves the analysis of a saturated head space of Hg 0 vapour kept at a defined temperature, is widely used but a discrepancy of 8% was noted 25 between the calibrant gas output from this approach and the output from the new SI-traceable approach. This indicated a problem with the former that is a concern because of its wide use.…”

Primary Measurement of Gaseous Elemental Mercury Concentration with a Dynamic Range of Six Decades

“…In addition to the above-mentioned gravimetrically linked generators, other methods for quantifying GEM include use of the Hg-saturated vapor pressure equation via the Bell-jar method 12−15 and use of Hg SRM 3133. 11 All cases require use of an SI-traceable reference material containing a known amount fraction of mercury. Laser absorption spectroscopy (LAS) in the ultraviolet (UV) spectral region provides a pathway for high sensitivity and potentially reference material-free measurement of the amount-of-substance.…”

“…An independent route to SI traceability for primary GEM mass concentration generation has been established by the Van Swinden Laboratory, which is the National Metrology Institute of the Netherlands. They use an isothermal suite of GEM-containing diffusion cells with a range of capillary diameters and gravimetrically establish their mercury mass flow rate. − The effluent from each cell is subsequently mixed with a steady stream of nitrogen (N 2 ) diluent gas at constant pressure, temperature, and volumetric flow rate. Through various combinations of diffusion cells and dilution gas flow rates, GEM concentrations between 0.1 μg m –3 and 2.1 μg m –3 with u r (ρ) = 1.5% and between 5 μg m –3 and 100 μg m –3 with u r (ρ) = 0.9% have been demonstrated .…”

“…In addition to the above-mentioned gravimetrically linked generators, other methods for quantifying GEM include use of the Hg-saturated vapor pressure equation via the Bell-jar method − and use of Hg SRM 3133 . All cases require use of an SI-traceable reference material containing a known amount fraction of mercury.…”