WP 1

Calibration gases for existing air quality directive pollutants at limit values (LV)

The aim of this work package is to provide harmonized preparative dilution methods of air pollutants gases for calibration and quality control purposes in air quality monitoring where a need for improved methodologies is present.

The work focuses on the reactive gases NO₂ and SO₂, at concentration levels corresponding to the limit values given in the Air Quality Directive (2008/50/EC) for the measurement of ambient air pollutants. Nitrogen oxide (NO) is normally measured in combination with nitrogen dioxide for the measurement of NO_x. Although NO is a reactive gas, reference standards at air quality concentration levels have proven to be quite stable. Therefore NO will be used as test gas to validate the activities of this WP. For the other gaseous air pollutants of the air quality directive, carbon monoxide, ozone and benzene, no specific needs have been identified in the preparation of calibration gases at limit values (LV).

*Air Quality Directive (2008/50/EC) Annex XI and Annex XIII

It should be noted that NMIs have developed dilution methods for NO, NO₂ and SO₂. However, recent CCQM key-comparisons (CCQM-K26b, CCQM-K46) have shown significant differences in results between gravimetric and dynamic methods and the reasons why are not understood. The concentration ranges under investigation will be between annual and hour limit values, to support the current needs of monitoring networks.