WP 2

Zero gas standards

The aim of this workpackage is to reduce the uncertainty in the measurement of chemical pollutants in air by improving the measurement capabilities for impurities in zero gas. The requested levels at which the impurities in zero gas have to be determined can currently not be met for three reasons:

• Commonly used measurement techniques require calibration at zero and span level

• No zero gas standards with given uncertainty available

• Lack of sensitivity of equipment

The impact on the measurement of chemical pollutants in air at the requested levels already gives an added uncertainty between 1% and 5% relative and will be higher when the composition of the zero gas cannot be guaranteed.

WP2 is focusing on SO₂, NO and NO₂ pollutants included in the EU air quality directive.

A number of analytical techniques will be tested for their suitability in detecting the impurities listed in the documentary standards related to “reference measurement methods for SO₂, NO and NO₂” (prEN14211 and prEN14212). These techniques will be used to perform measurement of impurities in zero gas at ppb and sub-ppb level. Special attention will be given to the measurement of ammonia and to its adsorption effect by cavity-ring-down spectroscopy (CRDS). In addition, measurement strategies, based on existing spectroscopic techniques, will be investigated to detect different impurity species simultaneously. Once analytical techniques and measurement procedures are fully traceable, this measurement approach will also be used to test cleaning devices, filters and scrubbers that will be used to supply zero gas. To ensure the quality of the measurements, a certification protocol for zero gas standards that apply the chosen analytical techniques will be prepared.

The challenging chemicals are SO,sub>2, NO, NO₂ and NH₃ measured at least at half of the specification limit given in the (draft) documentary standards prEN14211 and prEN14212. Specifications of the relevant impurities in zero gas for the measurement of SO,sub>2, NO and NO₂ are reported in the table below. Further, the traceability of the measurement results should be guaranteed.

List of specifications of the impurities in zero gas