The aim of WP3 is to develop optimised and validated sampling methods for gaseous Hg species using traceable reference standards for Hg(0) and Hg(II). As part of this the reference gas standard and calibration method from WP1 will be used for validation.
The outputs from WP3 will also be used to support the on-line Hg field measurements in WP4 by providing traceable sampling methods for gaseous Hg species. Currently no traceable sampling protocols for Hg(II) measurements exists and therefore the work in WP3 is based on recognised serious analytical challenges related to Hg(II) sampling. These challenges are mainly due to complex surface and gas-phase chemistry in both the atmosphere and especially in stack emissions, which can alter Hg speciation during sampling.
The aims of the tasks in WP3 are:
Task 3.1: To investigate how atmospheric and stack gas emissions chemistry influences Hg sampling and measurement. This will be undertaken by investigating the formation of oxidised Hg species in the atmosphere and in stack gas emissions, using a box model in order to gain a theoretical understanding of the ‘actual’ nature of Hg species in the atmosphere and in stack gas emissions.
Task 3.2: To use the theoretical understanding from Task 3.1 to identify the critical components and parameters, that can alter Hg speciation during sampling and to study these processes using tracer experiments. In addition, sampling methods for atmospheric Hg speciation and stack gas emission will be developed using the calibration methods and reference gas standards developed in Tasks 1.1-1.3.
Task 3.1: Hg chemistry in the atmosphere and stack gas emissions
The aim of this task is to investigate how atmospheric and stack gas emissions chemistry influences Hg sampling and measurement. This will involve investigating the formation of oxidised Hg species in the atmosphere using a box model.
Isotopic signatures of Hg clearly show that there are intense photochemical reactions in the atmosphere that severely impact the isotopic signatures of Hg creating large isotopic anomaly signatures such as mass independent fractionation. UPPA will evaluate the wavelength dependence and intensities of these fractionations using Hg(0) gaseous vapour in laboratory photochemical reactions. The contribution of other important gaseous species and radicals known to direct atmospheric reactions will be tested in a laboratory box model chamber
| Activity number | Activity description | Partners (Leadinbold) |
|---|---|---|
| A3.1.1 | CNR, JSI and UPPA will undertake a theoretical review of the practical issues relating to Hg speciation and fractionation. This review will consider different Hg oxidation states (Hg(0), Hg(I), Hg(II)), and their chemical species in the atmosphere and in stack gas emissions. Specifically, CNR will investigate Hg(0) and oxidised Hg species in the atmosphere (gaseous, dissolved and particle bound species). JSI will investigate Hg speciation in stack gas emissions. UPPA will address heterogeneous chemical reactions involving Hg and the chemistry and physics of reactions at environmental interfaces (gaseous, solid and liquid) and stack gas emissions. | CNR, JSI, UPPA |
| A3.1.2 | Using the outcome of A3.1.1, CNR will develop chemical mechanism modules to be included in a box model based on the Kinetic Pre-Processor (KPP). KPP permits a series of chemical reactions and their respective rates to be included in a single module, these ‘equation modules’ will then be used to construct an overall chemical mechanism ‘ad hoc’ in order to produce a box model for a specific situation. The box model will predict the evolution of the chemical composition of a given chemical environment. The box models can thus include modules to describe aerosol composition and the heterogeneous interactions involving gas phase Hg(II) compounds, Hg(II) compounds associated with PM and Hg(II) compounds found in cloud and rain water, and in flue gas and stack plumes. The output of the box model will be a better understanding of the actual nature of oxidised Hg in the atmosphere and stack gas emissions. | CNR |
| A3.1.3 | Using the box model from A3.1.2, CNR will investigate potential Hg redox reactions with halogens, sulphur oxides and water in the gas phase and on surfaces in various applications. This will be undertaken by CNR, with support from VTT, Optoseven and PSA, according to the conditions of the field test sites in Tasks 4.1 and 4.2 and using the optimised sampling methods from Task 3.2 i.e. CNR will modify the chemical box model using the outcomes of A3.2.6, A4.1.5 and A4.2.4. This revision will be an on-going activity that will be undertaken in parallel with input coming from A4.1.5 and A4.2.4 (i.e. these activities do not have to be fully completed before the revision can commence). |
CNR, VTT, Optoseven, PSA |
| A3.1.4 | UPPA will experimentally measure the mass independent fractionation of gaseous Hg(0) at specific wavelengths (e.g. from UV to infrared) and with potential reactive gaseous species of relevance in the air (e.g. Hg and other volatile species). The results will be used to better understand the isotopic signatures of Hg species returning to surface ecosystems. The results will used for D4 (D2.2.10). | UPPA |
Task 3.2: Sampling of Hg(II) and Hg(0) in the atmosphere and stack gas emissions
Complex surface and gas-phase chemistry in the atmosphere and stack gas emissions can alter reactions and Hg speciation during sampling. General environmental conditions such as temperature, humidity, UV, industry/source specific matrix effects, higher temperatures and Hg concentration ranges, potential back reactions and interferences during conversion of Hg(II), transport reactions and losses etc. can also vary significantly over time, and thus can affect Hg species capture efficiency, surface chemistry and sample preservation. Further to this, the inlet design, type of coatings and the temperature of collection surfaces for Hg(II) and Hg(0) sampling, as well as possible transport losses and species conversions during sampling and from the probe to detector can also have significant effects.
Therefore, the aims of this task are:
- to identify the critical components and parameters, based on the results of Task 3.1, that can alter Hg speciation during sampling and study these processes using tracer experiments.
- to develop sampling methods for atmospheric Hg speciation and stack gas emissions using the calibration methods and reference gas standards developed in Tasks 1.1-1.3.
| Activity number | Activity description | Partners (Leadinbold) |
|---|---|---|
| A3.2.1 | CNR, JSI, PSA, and UPPA will evaluate at least 2 commonly used speciated Hg sampling methods for atmospheric and stack gas emissions (i.e. as defined by partners and the stakeholder committee A5.1.1) in terms of understanding the nature of oxidised Hg in the atmosphere and stack gas emissions. This will be undertaken in parallel with A3.1.2 and will relate to sampling steps for preconcentration in atmospheric measurements and in stack gas emissions, filtration, dilution with dry air, thermal conversions, and transportation of Hg species from probe to detector. At this stage in the project only the available calculations from the box model in A3.1.2 are required. From this CNR, JSI, PSA, and UPPA will identify critical components and parameters that can alter Hg speciation during sampling. |
CNR, JSI, PSA, UPPA |
| A3.2.2 | Based on the outcome of A3.2.1, tracer experiments will be designed by JSI and UPPA to study the stability of Hg and its species, conversion, losses and artefact formations during the following sampling steps: preconcentration in atmospheric measurements (cryotrapping, impingers, denuders, selective trapping for Hg species, passive sampling methods) preconcentration in stack gas emissions (sorbent traps, on-line sampling systems for the monitoring of flue gas Hg speciation) filtration, dilution with dry air, thermal conversions, transportation of Hg species from probe to detector. Both LGC and UPPA will use enriched stable isotopes to study the sampling steps and JSI will use the very sensitive radioactive 197-Hg to quantify them. |
LGC, UPPA, JSI |
| A3.2.3 | Based on the results obtained in A3.2.2, at least 2 artefact free sampling methods will be developed by CNR, JSI, UPPA, VTT, Optoseven, PSA and LGC. The 2 artefact free sampling methods will be for (i) atmospheric measurements and (ii) stack emissions. Both will be validated using the calibration methods and reference gas standards developed in A1.1.4 and A1.3.1. Specifically, the artefact free sampling method for atmospheric measurements will be validated by CNR, JSI, UPPA and LGC. Optoseven, PSA and VTT will validate the artefact free sampling method for stack emissions. |
CNR, JSI, UPPA, VTT, Optoseven, PSA, LGC |
| A3.2.4 | UPPA and JSI will develop SI traceable methods to accurately determine Hgtot isotopic ratio signatures, and species specific Hg(II) and Hg(0) from denuders, sorbent traps, and impinger solutions using the sampling methods developed in A3.2.3. This will include an investigation of mass bias correction procedures to overcome mass discrimination. | UPPA, JSI |
| A3.2.5 | Using input from A3.1.1, A3.1.2 and A3.2.1-A3.2.4, JSI, CNR, UBA, UPPA, LGC, VTT, Optoseven and PSA will produce optimised and validated sampling methods for gaseous Hg species using traceable reference standards for Hg(0) and Hg(II)). | JSI, CNR, UBA, UPPA, LGC, VTT, Optoseven, PSA |
| A3.2.6 | JSI with support from CNR, UBA, UPPA, LGC, VTT, Optoseven and PSA will review the methods from A3.2.5 and the coordinator will then submit it to EURAMET as D6 ‘Optimised and validated sampling methods for gaseous Hg species using traceable reference standards for Hg(0) and Hg(II))’. | JSI, CNR, UBA, UPPA, LGC, VTT, Optoseven, PSA |
