Laboratory And Field Inter-Comparison of O3 Diffusive Samplers

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A field and laboratory inter-comparison of diffusive samplers for measuring ozone (O3) in ambient air was carried out. The objective of this study was the evaluation, according to the EN protocol of validation of diffusive samplers, of the extent of differences between O3 measurements performed by diffusive samplers and the reference method under extreme conditions of influencing factors.

Ten leading European laboratories were invited to participate. The selected participants were responsible for the preparation and analysis of the samplers. The whole range of diffusive samplers commercially available on the market was included in the study.

The inter-comparison consisted of laboratory and field experiments. The laboratory tests took place in the exposure chamber developed by ERLAP, which can control the exposure parameters while ensuring homogeneous conditions for all the samplers.

Two field tests were performed, one rural and one urban site located in Switzerland and France, respectively. The rural test was performed at one of the NABEL (Swiss Air Pollution Monitoring Network) monitoring station located in Cadenazzo (CH) while the urban experiment was performed at one monitoring station (Genevilliers, F) of the automatic network of AIRPARIF.

The agreement of the O3 measured by the diffusive samplers with the reference method was satisfactory for the 1-week averaging time. For the 8 hours experiments, the diffusive samplers having high uptake rates were able to quantify the O3 concentration better than the samplers with low uptake rates. Moreover, the results of the field tests were in better agreement with the reference method than the results of the laboratory tests. This could be explained by the extreme conditions simulated during the laboratory experiments and by the presence in the exposure chamber of uncontrolled/unknown factors. The results of the field tests showed that the majority of diffusive samplers are suitable for exposure of 1 week and fulfil the 30% accuracy requirement of the European Directive.

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