The development of gas standards and calibration techniques for measurements of vehicle, aircraft and industrial emissions, natural gas, occupational exposure and air quality |
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Authors: | P E Holland Peter T Woods Chris Brookes I Uprichard Paul Quincey R Robinson Hansa D'Souza Martin Milton Brian Goody William Bell Des Alphonso |
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Institution: | (1) Centre for Optical and Environmental Metrology, National Physical Laboratory, Teddington TW11 0LW, UK e-mail: Paul.Holland@npl.co.uk Tel.: +44-181-943 7174 Fax: +44-181-943 6755, GB |
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Abstract: | The National Physical Laboratory (NPL) is involved in the dissemination of nationally traceable standards to which measurements
of air quality, occupational exposure and air pollution source emissions, and natural gas analyses, can be referenced. This
has required the development of national primary gas standards using absolute gravimetric and other techniques, and the development
of dynamic calibration techniques for gaseous species which would be unstable in high-pressure cylinders. The methodology
used for preparing gas standards gravimetrically is described, together with the rigorous quality assurance measurements and
consistency checks which are used to demonstrate their accuracy and stability. The uncertainty budget assigned to these standards
will also be summarised. NPL primary standards are used to certify traceable 'secondary' gas standards which are disseminated
so as to ensure the accuracy of gas analysis measurements. Examples of the applications of these secondary standards are presented.
The gas standards are employed in proficiency testing of industrial stack-testing organisations, and results of the initial
rounds are presented. NPL gas standards are also now being used as the basis of the United Kingdom Environment Agency's new
type-approval and certification scheme for continuous industrial stack-emission analysers. A recent important international
initiative, in the field of gas analyses, is the agreement by national standards laboratories across the world to demonstrate
the equivalence of their calibrations, by means of key comparisons between them. These worldwide key comparisons are complemented
in Europe through the EUROMET initiative which seeks to establish the equivalence and comparability of calibration standards
held at national standards laboratories across Europe. Examples of these intercomparisons are presented.
Received: 23 March 2000 / Accepted: 18 August 2000 |
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Keywords: | Traceability Gas standards Calibration Quality assurance Proficiency testing International comparisons |
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