Abstract
The existing Air Quality Directive 2008/50/EC establishes within the European Union (EU) member states limit values for fine air particulate matter (PM2.5) including the possibility to discount natural sources of pollution when assessing compliance with the legislation. In proving this, EU member states shall determine, amongst others, the rural background concentration of some anions (Cl−, NO3− and SO42−) and cations (Na+, NH4+, K+, Ca2+ and Mg2+). To deliver reliable data and to comply with the data quality objectives of the legislation, environmental control laboratories should use certified reference materials (CRMs) to validate or verify the performance of their analytical methods. Since no CRMs for anions and cations in PM2.5 are presently available, we present the commutability issues encountered during the first attempt to develop such a material. We demonstrate that a dust, collected in a road tunnel and previously used for the production of two CRMs of a PM10-like material, does not behave as an authentic fine particulate matter collected according to EN12341:2014 when measured by an established method proposed by the European Committee for Standardization (CEN/TR 16269:2011). The water-soluble fractions of SO42−, NH4+, K+, Ca2+ and Mg2+ in a PM2.5-like candidate CRM produced from that road tunnel dust are only fully extracted after 3 h of sonication and not after 30 min, as stated in the method. Moreover, we found that the particle size of the test material influenced the extraction yield of K+, Ca2+ and Mg2+, suggesting that these ionic species were incorporated in the core of the particles and inaccessible to the extraction procedure. These particular features make the material unsuitable for the measurements of ions with the CEN method. The difference in the extraction time can be seen as a commutability issue and the candidate CRM should be considered as not commutable with routine samples. This demonstrates that commutability studies should not only be considered for clinical CRMs, but also for inorganic CRMs when they are intended to be used to quantify operationally defined analytes.
Highlights
Airborne particulate matter (PM) cannot be considered as a single pollutant, but rather as a mixture of particles originating from different sources and containing many different chemical species
We report the results of a feasibility study of the candidate certified reference materials (CRMs) of PM2.5 currently under development which is intended to be certified for all the ions listed in the European Air Quality Directive
Applying the procedure described in the section above, the PM10-like starting material was successfully milled into a finer powder
Summary
Airborne particulate matter (PM) cannot be considered as a single pollutant, but rather as a mixture of particles originating from different sources and containing many different chemical species. To guarantee the accuracy of these measurements and compliance with the data quality objectives laid down in Directive 2008/50/EC, environmental control laboratories have to use adequate quality assurance and quality control tools and should ensure that all measurement results are traceable in accordance with ISO/IEC 17025 This can be achieved by using certified reference materials (CRMs) when validating or assessing performance of the analytical methods employed [3]. In contrast to other PM materials loaded on filters such as NIST SRM 2783, NIST RM 8785 and CRM SL-MR-2-PSF-01 [7,8,9], the new candidate CRM will be produced as a fine powder In such a physical form, materials are usually simpler to homogenise, more stable and easier to store and transport [4, 10]. The material was found to be homogenous and stable, and is currently undergoing characterisation
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