Validating an Evaporative Calibrator for Gaseous Oxidized Mercury

Area of Science:

• Environmental Chemistry
• Atmospheric Science
• Analytical Chemistry

Background:

• Accurate atmospheric mercury speciation is crucial for understanding mercury's biogeochemical cycle and improving climate models.
• Establishing metrological traceability for mercury speciation measurements is essential for data comparability.
• Traceability for elemental mercury is established, but gaseous oxidized mercury (GOM) traceability remains a challenge.

Purpose of the Study:

• To extensively evaluate the performance of a newly developed calibration unit for traceable gaseous oxidized mercury (GOM) calibrations.
• To assess the suitability of the calibration unit for measuring mercury chloride (HgCl2) and mercury bromide (HgBr2) gas concentrations.

Main Methods:

• Utilized a 197Hg radiotracer for validation of the calibration unit over a wide range of concentrations.
• Compared experimental and calculated values to determine recoveries and estimate adsorption enthalpy (ΔHads).
• Evaluated calibrator performance for both HgCl2 and HgBr2 gas calibration.

Main Results:

• Average recoveries for HgCl2 ranged from 88.5% at 1178 ng m-3 to 39.4% at 5.90 ng m-3, indicating significant losses due to adsorption.
• Estimated adsorption enthalpy (ΔHads) of -12.33 kJ mol-1 suggests exothermal adsorption of oxidized mercury.
• Recoveries for HgBr2 were significantly lower than for HgCl2, even at high concentrations.

Conclusions:

• The developed calibration unit is only suitable for HgCl2 concentrations above 1 µg m-3 due to concentration-dependent recoveries.
• The unit's performance limitations prevent its use for calibrating instruments for ambient GOM measurements.
• Further development is needed to improve the suitability of the unit for HgBr2 calibration, as it is often used as a proxy for atmospheric HgBr species.