Elevated Gaseous Oxidized Mercury Revealed by a Newly Developed Speciated Atmospheric Mercury Monitoring System

Abstract

Gaseous oxidized mercury (Hg2+) monitoring is one of the largest challenges in the mercury research field, where existing methods cannot simultaneously satisfy the measurement requirements of both accuracy and time precision, especially in high-particulate environments. Here, we verified that dual-stage cation exchange membrane (CEM) sampler is incapable of gaseous elemental mercury (Hg0) uptake even if particulate matter is trapped on CEM, whereas the Hg2+ capture efficiency of the sampler is more than 90%. We then developed a Cation Exchange Membrane-Coupled Speciated Atmospheric Mercury Monitoring System (CSAMS) by coupling the dual-stage CEM sampler with the commercial Tekran 2537/1130/1135 system and configuring a new sampling and analysis procedure, so as to improve the monitoring accuracy of Hg2+ and ensure the simultaneous measurement of Hg0, Hg2+, and Hgp in 2 h time resolution. We deployed the CSAMS in urban Beijing in September 2021 and observed an unprecedented elevated Hg2+ during the daytime with an average amplitude of 510 pg m–3. Using a zero-dimensional box model, the elevated Hg2+ production rate was attributed to high atmospheric oxidant concentrations, Hg0 heterogeneous and interfacial oxidation processes on the surface of atmospheric particles, or potential unknown oxidants.

Photochemical Reduction of Particle Bound Mercury in Atmospheric Aerosol Water

“…The main reasons may be could attributed to the high fractions of Cl, Br, and sulfate in aerosol and severe ozone pollution in Beijing, 34−36 since Br and ozone act as principal oxidants for GEM oxidation forming GOM. 5,37 These PBM species at Beijing were a bit different from a prior study conducted in Canada, 22 of which HgO, HgCl 2 , and HgS of PBM accounted for 41%, 23%, and 9%, respectively. In terms of mercury isotopic compositions of PBM, significantly negative MDF and slightly negative even-MIF and positive odd-MIF signatures were found (Figures 1c,d and S5).…”

“…In detail, the water-soluble speciations (e.g., HgCl 2 , HgBr 2 ) dominate PBM chemical compositions (together occupy of 48.1%), and the insoluble species of HgO and HgS/HgSO 4 accounted on average for 17.3% and 16.0% of PBM, respectively. The main reasons may be could attributed to the high fractions of Cl, Br, and sulfate in aerosol and severe ozone pollution in Beijing, − since Br and ozone act as principal oxidants for GEM oxidation forming GOM. , These PBM species at Beijing were a bit different from a prior study conducted in Canada, of which HgO, HgCl 2 , and HgS of PBM accounted for 41%, 23%, and 9%, respectively.…”

Measurement of Atmospheric Mercury: Current Limitations and Suggestions for Paths Forward

“…When loading CEM with GOM in the laboratory, all GOM is captured, while in the field, breakthrough is typically on the order of 10% (cf., refs , , ). Limited data suggest when there is PBM on the CEM, the CEM does not take up GEM …”

“…Limited data suggest when there is PBM on the CEM, the CEM does not take up GEM. 49 Concerns regarding the MerPAS method include the low time resolution (>1 month), thus short-term (<2 to 4 week and diel) variability will not be captured. It is unlikely that the low time resolution can be improved due to the method and the analytical detection limit.…”

Traceable Calibration of Atmospheric Oxidized Mercury Measurements

“…Hg II is present at ultratrace levels in the atmosphere (low pg m –3 ), making it difficult to measure accurately and precisely. Measurements of atmospheric Hg II were previously made with commercial systems that utilized a KCl-coated denuder, which is now known to be biased low. − Cation exchange membrane-based systems appear to avoid the low bias created by the KCl denuder and have been deployed at many locations around the globe. − Most measurements of Hg II have been uncalibrated, however, including those made with cation exchange membranes, making it difficult to assess their validity. A few groups have investigated methods to quantitatively calibrate measurements of Hg II , but further standardization studies are needed. − A recent review assessed that permeation tube-based systems are the best candidate currently available to calibrate ambient Hg II measurements, and permeation tube-based calibrators have previously been utilized in field settings. ,− …”