Assessment of uncertainty of benzene measurements by Radiello diffusive sampler

Abstract

The uncertainty of benzene measurements obtained by the analysis of thermally desorbable Radiello diffusive samplers was evaluated according to the recent standard EN 14662-4 [EN 14662-4, 2005. Ambient air quality. Standard method for measurement of benzene concentrations. Part 4: diffusive sampling followed by thermal desorption and gas chromatography]. Considering the results of laboratory experiments, all the sources of uncertainty regarding the diffusive sampler method characteristics were accessed for the sampling times of 7 and 14 days. The major part of the uncertainty budget (>79%) was explained by the variation of the sampling rate due to the environmental factors (temperature and concentration level). For weekly sampling, the diffusive sampler method satisfies the data quality objectives of the European Directive to supply the indicative measurements as well as the reference measurement, since the expanded uncertainty is found <25%. Using a model-predicted sampling rate which depends on the concentration and temperature, the expanded uncertainty is significantly decreased. The Radiello sampler was found to give correct results for a weekly sampling in a limited range of benzene concentrations between 0 and 10 μg m −3, which is generally observed in environmental air monitoring. This narrow validation domain limits the application fields of the Radiello sampler exposed for 7 days to indoor air, personal exposure and ambient atmospheric monitoring excluding workplaces. For 2-week sampling, the expanded uncertainty of measurements exceeds 30%. However, this diffusive sampler can still be used to carry out an objective evaluation of benzene (minimum quality objective for the accuracy of 100%). Therefore, the performance of this diffusive sampler method appears to be suitable for the benzene monitoring in ambiant air.