|Abstract Title:||Primary laser absorption spectroscopy method with a dynamic range of six decades for measuring amount of gaseous elemental mercury|
|Presenter Name:||Mr Qingnan Liu|
|Co-authors:||Dr Joseph T. Hodges|
|Company/Organisation:||National Institute of Standards and Technology|
Abstract Information :
The reduction of anthropogenic mercury emissions is a global effort, garnering commitment from nearly 137 countries in the 2017 Minamata convention. In the US the EPA-mandated Mercury and Air Toxics Standards regulates industrial emissions, thereby driving the application of continuous emissions monitoring for accurate field measurements of mercury. To establish compliance the National Institute of Standards and Technology (NIST) developed an SI-traceable certification program for vendor Hg-in-air generators, which are in turn used for CEMS calibrations. Historically, in this program the mercury emitted by a NIST prime Hg generator was value-assigned on the SI using an SRM 3133® Hg standard combined with isotope dilution cold vapor inductively coupled mass spectrometry measurements. To circumvent issues related to throughput, sample processing, and dependence on a reference material, Srivastava and Hodges (2018) applied a linear absorption spectroscopy method to measure the absolute number density of gaseous elemental mercury. With this approach, light absorption is described by the Beer-Lambert law and modelled in terms of the intrinsic atomic parameters of mercury and physical observables to obtain the analyte number density. In this presentation, we describe a dual-cell approach to achieve a measurement range spanning six decades from 1 ng m-3 (representative of ambient levels) to an upper bound of 1000 gm-3 (representative of high anthropogenic source emission levels). The resulting relative standard uncertainties are 0.5% across the mass concentration range 0.25 μg m–3 to 1000 μg m–3.