Session Title :

Traceability of mercury measurements

Synopsis :

The main purpose is to present the latest developments in the area of traceable mercury measurements worldwide. This special session is intended for specialists in mercury measurements in air and emissions, national metrology institutes and bodies/agencies responsible for standardisation and reference methodologies, and producers of instrumentation.

Description :

Mercury is a trace component of all fossil fuels, including natural gas, gas condensates, crude oil, coal, tar sands, and other bitumens. Natural sources such as volcanoes are responsible for about half of the atmospheric mercury emissions, whereas the human generated half exists for about 65% of mercury emitted due to stationary combustion, of which coal-fired power plants contribute most. Natural mercury emissions due to reduction and evaporation from the ocean surface, and degassing from soils, account for almost half of the elemental mercury present in the global atmosphere. Therefore accurate determination of dissolved gaseous mercury in water, and evaporation of elemental mercury from aqueous and terrestrial environment is of great importance in the development of regional and global mercury inventories and mass balances.

From the analytical point of view, elemental mercury is reactive, difficult to store and to handle, and extremely difficult to measure in a comparable way. The development of measurement methodology and primary standards for mercury in the vapour phase is urgently required to secure comparable ambient Hg measurement and emissions from point and disperse mercury sources. The main purpose is to present the latest development in the area of traceable mercury measurements worldwide. The majority of measurements of mercury vapour are currently traceable to the vapour pressure of mercury. A static head space generator (bell-jar apparatus) allows a saturated concentration of mercury to develop in air, from which a known amount of mass of mercury can be removed for calibration purposes. Several empirical equations are available to describe the vapour pressure of mercury at a given temperature, but the agreement between them is not good as data from different equations sometimes do differ 5% or even more. To remove the dependency of mercury vapour measurement on these empirical equations, and to provide stability and comparability, traceability needs to be developed for mercury measurement results to the SI system of units. Mercury speciation in the gaseous phase is even more challenging.

The special session is intended to bring together specialists in mercury analysis and speciation in air and emissions sources, national metrology institutes and bodies/agencies responsible for standardisation and reference methodologies, and producers of instrumentation.

The main topics to be addressed are:
Evaluation and comparison of existing and novel primary generation methods to obtain mercury gas standards
Validation and traceability of dynamic mercury vapour generators used for calibration of (automated) measuring systems at relevant low concentration levels
Traceability and reliability of measurements of mercury vapour in the gas phase (incl. air, natural gas and exhaust emissions)
Validation of stability and potential interspecies conversion at very low levels (ng/m3) during sampling, sample handling and storage
Realization of traceable primary standards and development of a facility to prepare gaseous mercury standards, including its measurement uncertainty budget
International programmes in need for traceable mercury measurements
Field experience and needs by the users groups (researchers and industries)
Progress on standardised methods to harmonise measurement of Hg vapour in air