Publication Date:
2013-11-29
Description:
Along with some research networking programs, the European Directive 2008/50/CE requires chemical speciation of fine aerosol (PM2.5), including elemental (EC) and organic carbon (OC), at a few rural sites in European countries. Meanwhile, the thermal-optical technique is considered by the European and US networking agencies and normalization bodies as a reference method to quantify EC–OC collected on filters. Although commonly used for many years, this technique is still suffering from a lack of information on the comparability of the different analytical protocols (temperature protocols, type of optical correction) currently applied in the laboratories. To better evaluate the EC–OC data set quality and related uncertainties, the French National Reference Laboratory for Ambient Air Quality Monitoring (LCSQA) has organized an EC–OC comparison exercise for French laboratories using different thermal-optical methods. While there is good agreement on total carbon (TC) measurements among all participants, some discrepancies can be observed on the EC/TC ratio, even among laboratories using the same thermal protocol. These results led to further tests on the influence of the optical correction: results obtained from different European Laboratories, confirming that there are higher differences between OCTOT and OCTOR measured with NIOSH 5040 in comparison to EUSAAR-2. Also, striking differences between ECTOT/ECTOT ratios can be observed when comparing rural and urban results whatever the thermal protocol ECTOT being 50% lower than ECTOT at rural sites whereas it is only 20% lower at urban sites. The PM chemical composition could explain these differences but the way it influences the EC–OC measurement is not clear and needs further investigations. Meanwhile, some additional tests seem to indicate an influence of the oven soiling on the EC–OC measurement data quality. This enlightens the necessity to follow the laser signal decrease with time and its impact on measurements. Nevertheless, this should be confirmed by further experiments, involving more samples and various instruments, to enable statistical processing. All these results provide insights to determine the quality of EC–OC analytical methods and may contribute to the work toward establishing method standardisation.
Electronic ISSN:
1867-8610
Topics:
Geosciences
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