Comparison and calibration of methods for ambient reactive mercury quantification

Area of Science:

• Environmental Chemistry
• Atmospheric Science
• Mercury Speciation

Background:

• Gaseous oxidized mercury (GOM) is the primary form of atmospheric mercury (Hg) deposited into ecosystems.
• Accurate and calibrated measurements of GOM are essential for understanding mercury cycling and environmental impacts.
• Existing measurement techniques require thorough evaluation for reliability and precision.

Purpose of the Study:

• To compare the performance of active membrane-based collection systems (RMAS) with dual-channel systems (DCS) and a Tekran speciation system for measuring GOM and reactive mercury (RM).
• To assess the accuracy and long-term precision of a custom-built automated calibration system for mercury speciation instruments.
• To identify limitations and interferences associated with different atmospheric mercury measurement methodologies.

Main Methods:

• Co-location of two RMAS, two DCS, and one Tekran 2537/1130 system for one year.
• One DCS was coupled with a custom automated calibration system using gaseous elemental mercury (GEM), HgBr2, or HgCl2.
• Gaseous oxidized mercury (GOM), particulate-bound mercury (PBM), and reactive mercury (RM = GOM + PBM) were quantified.

Main Results:

• The Tekran system measured significantly less GOM (~14.5%) compared to the other systems.
• DCS and RMAS showed significant correlation, but DCS measurements were higher (50% and 30% higher than RMAS).
• The automated calibration system demonstrated consistent performance, and the DCS accurately recovered injected GOM, indicating DCS accuracy for RM/GOM measurement.

Conclusions:

• Both calibrated and uncalibrated DCS provide accurate measurements for reactive mercury (RM) and/or GOM.
• Active membrane-based collection systems (RMAS) may experience some mercury loss from membranes during sampling.
• Dual-channel systems offer a reliable method for atmospheric reactive mercury monitoring, complementing other techniques.