Feasibility Study of Preparation and Certification of Reference Materials for Nitrogen Dioxide and Sulfur Dioxide in Diffusive Samplers

Abstract

Feasibility study of preparation and certification of reference materials for nitrogen dioxide and sulfur dioxide in diffusive samplers Michel Gerboles*, Daniela Buzica, Luciano Amantini, Friedrich Lagler and Theo Hafkenscheid+ European Commission - Joint Research Centre, Institute for Environment and Sustainability, Emissions and Health Unit, 21020 Ispra, Italy. Fax: +39-332-785652; Tel: +39-332-789364; E-mail: [email protected] +Dutch Measurement Institute, Delft, Netherlands This paper presents the results of a feasability study for the preparation and certification of reference materials (RMs) for nitrogen dioxide (NO2) and sulphur dioxide (SO2) in diffusive samplers. RMs for NO2 were prepared by exposure to gas mixtures in a chamber while the RMs for SO2 were prepared by liquid spiking. Certification of RMs for NO2 was found feasible with a certified uncertainty of 5.8 % and a proposed shelf life of 5 years. The uncertainty was calculated with contribution from the homogeneity of preparation, stability and transport of the CRMs and from an external verification of the certified value. To reach 5.8 % of uncertainty, the contribution of the differences between the results of analysis by ion chromatography and colorimetry must be eliminated. It is proposed to solve this by pre-extracting the samplers with water before analysis. The results of this study indicate that the samplers are stable for at least two years before and after exposure when stored in refrigerator. On the opposite, the certification of RMs for SO2 was found not feasible due to instability problems. This instability was attributed to reaction of sulfate on the walls of the samplers. Alternatively, the preparation of RMs by simultaneous exposure to SO2 and NO2 have been tested. Satisfying homogeneities has been reached both for NO2 and SO2.JRC.H.4-Transport and air qualit