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Interim EPA Traceability Protocols for the Qualification and Certification of Elemental and Oxidized Mercury Gas Generators

For regulatory purposes, mercury (Hg) calibration gas standards of known concentration and known uncertainty are needed to quality-assure data recorded by Hg continuous emission monitoring systems (CEMS) and measurements made with instrumental Hg reference test methods. Two interim EPA traceability protocols have been prepared that establish procedures for the qualification and certification of elemental and oxidized mercury gas generators. The interim protocols reflect the current state of development for generating and quantifying elemental Hg and mercuric chloride (HgCl2), a form of oxidized mercury.


The interim elemental Hg gas traceability protocol provides procedures to: (1) establish the quantitative output (i.e., “calibration”) of elemental Hg generators; and (2) determine the expanded, combined uncertainty values of the gas standards produced by the elemental Hg generators. The protocol also specifies the maximum allowable uncertainty for the elemental Hg gas standards. A Companion Document has also been prepared that summarizes the methodology used to calculate the certified elemental mercury gas concentrations and associated expanded, combined uncertainty values and includes example calculations of these certified gas concentrations and uncertainty values. Additionally, a series of generic elemental Hg generator spreadsheets have been prepared as templates for calculating these values.


The interim oxidized Hg gas traceability protocol provides procedures for: (1) establishing the NIST traceability and quantitative performance of key components of HgCl2 generators; (2) determining the uncertainty contributed by each of these components; and (3) calculating certified output concentrations and expanded, combined uncertainty values for the gas standards produced by the generators. This protocol also specifies a target uncertainty for the HgCl2 gas standards.


For continuous emission monitoring system (CEMS) applications, these interim protocols apply only to Hg monitoring system span values greater than or equal to 5.0 micrograms per cubic meter (µg/m3).


If you have comments or questions regarding these files, please contact Scott Hedges by e-mail at hedges.scott@epa.gov, or by phone at 202-343-9622 or Robin Segall by e-mail at segall.robin@epa.gov, or by phone at 919-541-0893. If possible, please submit your comments by e-mail.


Interim EPA Traceability Protocol for Qualification and Certification of Elemental Mercury Gas Generators (PDF 39pp 178 KB)


A Companion Document entitled, Treatment of Elemental Mercury Gas Generator Certification Data and Calculation of Uncertainty in support of the Interim EPA Traceability Protocol for Qualification and Certification of Elemental Mercury Gas Generators. (PDF 20pp 215 KB)



Five Generic Spreadsheet Files to calculate the certified elemental mercury gas concentrations and associated uncertainty values: (Note: In addition to using these generic spreadsheets, it is recommended that you contact your specific mercury generator vendor to see if they have vendor-specific spreadsheets you can use.)


Certification from Bracketing (Excel, 113 KB) - This workbook can be used at several steps in the certification process (i.e., certifying Vendor Prime, Field Reference, or User generators), but is most likely to be used by a vendor, since its primary purpose is to bring together results from dual-bracketing or multi-bracketing certification procedures. It is not specific to the type of detection technology (such as a concentrating detector developed by Tekran or a continuous detector developed Thermo-Fisher Scientific). Vendors who do not have their own certification spreadsheet/software must use this workbook (along with the appropriate companion workbook below) for certifying Field Reference generators.


Concentrating Detector Bracketing Only (Excel, 2.47 MB) - This workbook processes the data from one bracketing procedure using a concentrating detector. It is not a stand-alone certification workbook. It is a companion to the "Certification from Bracketing.xls" workbook which receives processed data from two or more "Bracketing only" workbooks to certify generators. Vendors are the most likely users (using it to certify Field Reference generators), though field analysts may choose this certification option for User generators (e.g., if incorporating the Type-B default reproducibility causes the target uncertainty to be exceeded).


Continuous Detector Bracketing Only (Excel, 738 KB) - This workbook processes the data from one bracketing procedure using a continuous detector. It is not a stand-alone certification workbook. It is a companion to the "Certification from Bracketing.xls" workbook which receives processed data from two or more "Bracketing only" workbooks to certify generators. Vendors are the most likely users (using it to certify Field Reference generators), though field analysts may choose this certification option for User generators (e.g., if incorporating the Type-B default reproducibility causes the target uncertainty to be exceeded).


User Generator Certification with Concentrating Detector (Excel, 2.50 KB)- The primary purpose of this workbook is to provide a time-efficient option for certifying User generators in the field, though the interim elemental Hg gas protocol does not currently prohibit its use for certifying User generators at vendor facilities. The workbook is specific to concentrating detectors. It can not be used to certify Vendor Prime or Field Reference generators, because it only supports the Type-B default reproducibility calculation.


User Generator Certification with Continuous Detector (Excel, 782 MB)- The primary purpose of this workbook is to provide a time-efficient option for certifying User generators in the field, though the interim protocol does not currently prohibit its use for certifying User generators at vendor facilities. The workbook is specific to continuous detectors. It can not be used to certify Vendor Prime or Field Reference generators, because it only supports the Type-B default reproducibility calculation.


Interim EPA Traceability Protocol for Qualification and Certification of Oxidized Mercury Gas Generators.


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