A traceable and continuous flow calibration method for gaseous elemental mercury at low ambient concentrations

Abstract

Abstract. The monitoring of low gaseous elemental mercury (GEM) concentrations in the atmosphere requires continuous high-resolution measurements and corresponding calibration capabilities. Currently, continuous calibration for GEM is still an issue at ambient concentrations (1–2 ng m−3). This paper presents a continuous flow calibration for GEM, traceable to NIST 3133 Standard Reference Material (SRM). This calibration approach was tested using a direct mercury analyser based on atomic absorption spectrometry with Zeeman background correction (Zeeman AAS). The produced continuous flow of GEM standard was obtained via the reduction of Hg2+ from liquid NIST 3133 SRM and used for the traceable calibration of the Zeeman AAS device. Measurements of atmospheric GEM using the calibrated Zeeman AAS were compared with two methods: (1) manual gold amalgamation atomic fluorescence spectrometry (AFS) calibrated with the chemical reduction of NIST 3133 and (2) automated gold amalgamation AFS calibrated using the mercury bell-jar syringe technique. The comparisons showed that a factory-calibrated Zeeman AAS device underestimates concentrations under 10 ng m−3 by up to 35 % relative to the two other methods of determination. However, when a calibration based on NIST 3133 SRM was used to perform a traceable calibration of the Zeeman AAS, the results were more comparable with other methods. The expanded relative combined uncertainty for the Zeeman AAS ranged from 8 % for measurements at the 40 ng m−3 level to 91.6 % for concentrations under 5 ng m−3 using the newly developed calibration system. High uncertainty for measurements performed under 5 ng m−3 was mainly due to instrument noise and concentration variation in the samples.

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

“…However, an uncertainty analysis has not been published for this instrument. To measure ambient concentrations, this instrument requires additional low-level calibration (e.g., ref .). These two instruments have been the primary methods for measuring atmospheric Hg since 2000.…”

“…For the Lumex instrument, the detector can only detect GEM, but interferences caused by conversion of GOM and PBM to GEM after deposition to inlet filters and other surfaces upstream of the detector, similar to the Tekran 2537 unit, is a possibility. Recent enhancements in sensitivity and tailored calibration settings underscore its capacity for precise low-level measurements …”

“…Recent enhancements in sensitivity and tailored calibration settings underscore its capacity for precise low-level measurements. 32 ■ MEASUREMENTS OF GOM AND PBM Current Methods. KCl-Coated Denuders.…”