Comparison of Reactive Gaseous Mercury Collection by Different Sampling Methods in a Laboratory Test and Field Monitoring

Accurately measuring reactive gaseous mercury (RGM) concentrations in the atmosphere is important to improve our understanding of the global mercury (Hg) cycle. In this study, we compared the RGM collection efficiencies of four sampling methods, including a 14 cm long KCl-coated denuder, a KCl-coated glass fiber filter, a KCl-coated quartz sand tube, and a cation exchange membrane. Both laboratory studies and field RGM monitoring were performed in environments with low humidity [relative humidity (RH) of ∼20%], medium humidity (RH of 50-70%), and high humidity (RH of ∼100%). Laboratory results showed that in environments with <70% RH, RGM amounts collected by the KCl-coated glass fiber filter and the KCl-coated quartz sand tube were comparable with those collected with the cation exchange membrane. In environments with ∼100% RH, the cation exchange membrane collected more RGM, approximately 1.1-1.4, 1.1-1.2, and 2.4-2.7 times more than the KCl-coated glass fiber filter, KCl-coated quartz sand tube, and KCl-coated denuder, respectively. During field monitoring, RGM amounts collected with the KCl-coated quartz sand tube were comparable to those collected with the cation exchange membrane regardless of the RH in the environment (p > 0.05; n = 60). Large variations (≤20 during field monitoring) in RGM concentrations measured by different sampling methods indicate the need for a unified and standardized method for future RGM monitoring.