Standardisation of a European measurement method for the determination of total gaseous mercury: results of the field trial campaign and determination of a measurement uncertainty and working range† Richard J. C. Brown, * a N. Pirrone, b C. van Hoek, c F. Sprovieri, d R. Fernandez e and K. Tot e f Received 27th November 2009, Accepted 18th December 2009 First published as an Advance Article on the web 12th January 2010 DOI: 10.1039/b924955a Working Group 25 of the European Committee for Standardisation’s (CEN) Technical Committee 264 ‘Air Quality’ is currently finalising a standard method for the measurement of total gaseous mercury (TGM) in ambient air, in response to the requirements of the European Union’s Fourth Air Quality Daughter Directive (4 th DD). We report the results of a programme of field measurements and the statistical analysis performed to assess the uncertainty of the proposed standard method, define its working range and determine its compliance with the required data quality objectives of the Fourth Air Quality Daughter Directive. The statistical analysis has shown that the maximum relative expanded uncertainty of 50% allowed by the 4 th DD is met down to a mercury mass concentration of approximately 0.75 ng m 3 , and that the dominant contribution to this uncertainty is systematic bias between instruments, mainly arising from the uncertainty in the calibration of the instruments. Introduction Ambient air quality has always been an important issue for humans and the environment. More recently, definitive links have been identified between pollutants and adverse effects on human health and on environmental sustainability. The Euro- pean Commission (EC) is acting to reduce human and environ- mental exposure to a variety of air pollutants across Europe. 1 Because of mercury’s combined qualities of toxicity, environ- mental persistence, and potential for bioaccumulation, it is an important pollutant to monitor and manage and indeed, the EC’s Fourth Air Quality Daughter Directive (4 th DD) 2 requires the monitoring of total gaseous mercury (TGM) (as well as nickel, arsenic and cadmium in the PM 10 particulate phase) in ambient air by all Member States. The population is exposed to mercury in ambient air mainly via TGM, and the vast majority of this mercury vapour is elemental mercury (except at some industrial and coastal locations where a significant proportion of the gaseous mercury may comprise oxidised mercury in compounds such as mercury (II) chloride, or organics such as methyl mercury—referred to as reactive gaseous mercury). 3 The 4 th DD defines TGM as ‘‘elemental mercury vapour and reactive gaseous mercury, i.e. water-soluble mercury species with sufficiently high vapour pressure to exist in the gas phase.’’ However, sampling and analysis of mercury are not always simple matters, and it is important to understand the key measurement issues to appropriately collect and interpret data. The application of non-validated sampling and analytical methods could lead to significant biases in measurement results. Therefore, there is a strong need to develop fully validated and traceable European standard methods that will ensure the representativeness, comparability, traceability and accuracy of data produced by all Member States for mercury measurements. For this reason the EC asked the European Committee for Standardisation (CEN) 4 to develop a standard method for the measurement of TGM in ambient air, as it has done for many other ambient pollutants, which may then if appropriate be a Analytical Science Team, National Physical Laboratory, Teddington, Middlesex, UK TW11 0LW. E-mail: richard.brown@npl.co.uk; Fax: +44 (0)20 8614 0423; Tel: +44 (0)20 8943 6409 b CNR IIA, CNR-Institute of Atmospheric Pollution Research, Rome, Italy c NEN, Dutch Standardization Institute, Delft, Netherlands d CNR IIA, CNR-Institute of Atmospheric Pollution Research, Rende, Italy e Instituto de Salud Carlos III, Majadahonda, Madrid, Spain f The Flemish Environment Agency, VMM, Antwerp, Belgium † Electronic supplementary information (ESI) available: The daily average total gaseous mercury concentrations measured at each site are tabulated in Tables S1 – S4. See DOI: 10.1039/b924955a Environmental impact This paper reports the results of a programme of field measurements and the statistical analysis performed on the data obtained to assess the uncertainty and the applicability of a proposed European standard method to measure total gaseous mercury (TGM) in ambient air. The results presented have an important environmental impact as they underpin the validity and performance char- acteristics of the method and help to ensure that all measurements made across Europe using this method are accurate and comparable. Consequently this will enable ambient concentration levels and long term concentration trends of this increasingly important pollutant to be assessed with confidence throughout Europe. This journal is ª The Royal Society of Chemistry 2010 J. Environ. Monit., 2010, 12, 689–695 | 689 PAPER www.rsc.org/jem | Journal of Environmental Monitoring