Limitations and insights regarding atmospheric mercury sampling using gold.

Area of Science:

• Environmental Science
• Analytical Chemistry
• Atmospheric Chemistry

Background:

• Atmospheric mercury (Hg) concentrations are typically measured using gold (Au) cartridges and thermal desorption atomic fluorescence spectrometry.
• The Tekran 2537 analyzer is the industry standard, but debate exists on whether it measures gaseous elemental mercury (Hg⁰) or total gaseous mercury (TGM).
• Existing Hg signal processing algorithms and calibration methods for atmospheric Hg analyzers have been questioned.

Purpose of the Study:

• To investigate the forms of mercury collected on gold cartridges using permeation tube-based calibrators.
• To understand the differences in Hg signal processing between Tekran 2537B and 2537X models.
• To evaluate various Hg⁰ calibration methods for atmospheric mercury analyzers.

Main Methods:

• Experiments utilized Hg⁰ and Hg^II permeation calibrators to assess gold cartridge performance.
• Analyzed Hg^II sampling and thermal desorption efficiency from gold cartridges.
• Compared Hg⁰ measurements from Tekran 2537B and 2537X models with different signal processing and calibration techniques.
• Evaluated the impact of a thermolyzer on Hg^II measurement.

Main Results:

• The Hg^II calibrator demonstrated reproducible permeation rates.
• Gold cartridges measured up to 75% of Hg^II, with initial measurements significantly lower due to adsorption.
• Thermal desorption reduced only 80% of Hg^II to Hg⁰; a thermolyzer increased Hg^II measurement to 97%.
• Tekran 2537X performance was independent of integration type, unlike the 2537B model.
• Bell jar calibration underestimated Hg⁰ concentrations by 6% ± 7% compared to permeation calibrator calibration.

Conclusions:

• Gold cartridges measure an atmospheric mercury fraction between Hg⁰ and TGM due to adsorption and incomplete Hg^II reduction.
• Accurate atmospheric mercury quantification necessitates distinguishing between Hg⁰ and TGM, as Hg^II can comprise up to 25% of total Hg.
• Using a thermolyzer or cation exchange membrane upstream of gold cartridges is recommended for TGM or Hg⁰ measurements, respectively.
• Traceable multipoint calibrations are crucial for mercury quantification, as different calibration methods yield varying results.