The development of gas standards and calibration techniques for measurements of vehicle, aircraft and industrial emissions, natural gas, occupationalexposure and air quality

The National Physical Laboratory (NPL) is involved in the dissemination of nationally traceable standards to which measurements of air quality, occupa tional exposure and air pollution source emissions, and natural gas analyse s, can be referenced. This has required the development of national primary gas standards using absolute gravimetric and other techniques, and the dev elopment 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 qual ity assurance measurements and consistency cheeks which are used to demonst rate their accuracy and stability. The uncertainty budget assigned to these standards will also be summarised. NPL primary standards are used to certi fy traceable 'secondary' gas standards which are disseminated so as to ensu re 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 resul ts: of the initial rounds are presented. NPL gas standards are also now bei ng used as the basis of the United Kingdom Environment Agency's new type-ap proval and certification scheme for continuous industrial stack-emission an alysers. A recent important international initiative, in the field of gas a nalyses, is the agreement by national standards laboratories across the wor ld to demonstrate the equivalence of their calibrations, by means of key co mparisons between them. These worldwide key comparisons are complemented in Europe through the EUROMET initiative which seeks to establish the equival ence and comparability of calibration standards held at national standards laboratories across Europe. Examples of these intercomparisons are presente d.