ESTABLISHING TRACEABILITY FOR MEASUREMENTS OF MERCURY VAPOUR IN AIR WINS NPL and P S ANALYTICAL RESEARCHER AWARD
The following research has recently been published in The Analyst (2008, 133,946-953), the Royal Society of Chemistry's high-impact analytical science journal. This work has been recognized as one of the three most significant research papers in Environmental science by CITAC (the Cooperation on International Traceability in Analytical Chemistry) and is one of the recipients of the ‘2008 CITAC Award for the Most Important Paper on Metrology in Chemistry’. This award is made to “highlight remarkable papers in the field of Metrology in Chemistry because of their important scientific content.”
Mercury is a highly toxic and persistent pollutant found in ambient, indoor and workplace air. It is released into the environment from sources such as coal-burning power plants, crematoria and waste treatment processes.
The vast majority of mercury vapour measurements currently undertaken are ultimately traceable to the vapour pressure of mercury. This is given in the scientific literature by several different empirical equations, but the agreement between these is not good, with data from different equations sometimes differing by 5% or more. There is also no current international agreement on which is the best equation to use.
In order to solve this important measurement issue, scientists at NPL (National Physical Laboratory) have collaborated with P S Analytical (a UK-based company specialising in instrumentation for trace elemental analysis) to link mercury vapour measurements directly to standards of mass thereby establishing traceability for these measurements to the SI system of units. These measurements are therefore no longer dependent on mercury vapour empirical equations and, crucially, measurements carried out by different laboratories at different times using different equipment, can be compared with confidence.
These outputs from the research are of great importance to the environmental chemistry community, particularly those engaged in air quality determination, and have many applications. For example, the traceability can be applied to the UK heavy metals monitoring network, which is operated on behalf of Defra by NPL (see Environmental Measures Issue 4 - Winter 2007) and requires the measurement of the ambient mercury vapour concentration at 15 monitoring sites across the UK. Other applications include the measurement of mercury vapour in indoor and workplace air - this is a particularly important issue as indoor levels of mercury are generally greater than those outdoors, and typical exposure times are longer.
This research gives the UK an advantage in preparing for the introduction of new European ambient air legislation. For example, work is on-going to bring in a standardised automatic method for the analysis of mercury vapour in ambient air as a possible replacement for the manual method in use in the heavy metals monitoring network.
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National Physical Laboratory(NPL) – The NPL is the UK's National Measurement Institute and is a world-leading centre of excellence in developing and applying the most accurate measurement standards, science and technology available. See www.npl.co.uk for further details
P S Analytical – Set up in 1983 P S Analytical are market leaders in the field of the monitoring and speciation of mercury, for further information visit our website at www.psanalytical.com