CEM - Abstract

Abstract Title: Gaseous oxidized mercury calibration by non-thermal plasma
Abstract Type: Oral
Session Choice: Mercury and Trace Metals
Presenter Name: Mr Jan Gacnik
Co-authors:Dr Igor Zivkovic
Mr Sreekanth Vijayakumaran Nair
Dr Joze Kotnik
Ms Andrea Jurov
Prof Milena Horvat
Company/Organisation: Jozef Stefan Institute
Country: Slovenia

Abstract Information :

Atmospheric mercury is the largest source of anthropogenic Hg pollution. As one of the atmospheric mercury species, oxidized mercury HgII is present in the atmosphere either directly due to emissions or indirectly through the oxidation of elemental mercury. Even though some HgII species, such as HgCl2 and HgBr2, have been identified in the atmosphere, the exact composition of atmospheric HgII remains unknown; this points to the need for improved atmospheric mercury speciation. Calibration for atmospheric mercury speciation is established for Hg0, but in the developmental stages for HgII. Available calibrations for HgII are based on either permeation or liquid evaporation. Although permeation and liquid evaporation calibrators are promising, they are still in the development stage, showing inconsistent results especially for ambient concentration levels. Inconsistent results most commonly originate from the absorptive nature of oxidized mercury. Additionally, these calibrators may also be subject to Hg0 impurities. To solve the problem of HgII calibration, we investigated the use of non-thermal plasma NTP, temperatures below 103 K oxidation of Hg0 to HgII. NTP was previously only employed for the removal of Hg0 in flue gases. The method was found to be cost effective with good oxidation efficiency. Oxidation reaction pathways, the influence of flue gas composition and the improvement of the Hg0 oxidation efficiency were all previously investigated for the removal of Hg0 in flue gases with NTP. rnOur work focused on generating a traceable amount of HgII species using NTP oxidation of Hg0 to HgII with the aim of SI-traceable calibration for atmospheric mercury speciation. The developed calibration was validated for flue gas and ambient gas HgII concentration levels using a highly sensitive and specific 197Hg radiotracer. From the validation, calibration recoveries were obtained with corresponding expanded uncertainties: 100.5 4.7 k2 for HgO, 96.8 7.2 k2 for HgCl2 and 77.3 9.3 k2 for HgBr2. In addition, the presence of each species was confirmed using temperature programed desorption and mass spectrometric measurements. Traceability to SI units was achieved by a chain of comparisons leading to the Standard Reference Material SRM 3133 Mercury Standard Solution. We also studied the thermal reduction of HgII to Hg0, as HgII species are typically converted back to Hg0 prior to analysis. The best thermal reduction efficiency gt;99.9 was achieved using an Al2O3 catalyst. rnNTP calibration for oxidized mercury therefore represents a viable option for HgII species calibration with the possibility to be used as a calibration for ambient Hg speciation as well as a calibration for continuous flue gas Hg measurements.rnrn