Evaluation of the field comparison exercise for PM10 and PM2.5, Ispra, January 18th - March 14th, 2018 : European Commission harmonization program for Air Quality Measurements

The Joint Research Centre of the European Union (JRC) is conducting proficiency tests for air pollutants regulated by European Directive [1]. For National Reference Laboratories of the EU participation is obligatory with the scope to demonstrate comparability between Member States. An inter-laboratory comparison exercise (ILC) for the determination of PM mass concentration with the reference gravimetric method (EN 12341:2014) was organised for the first time at European level in 2015 in Ispra, Italy. The second ILC of this kind took place in 2018. Such an ILC comprises the comparison between the samplers used by the various participants and includes the whole implementation of the reference method. Samplers are therefore co-located for several days so that the number of test samples is large enough for statistical analyses. Thanks to the great interest for this type of ILC and to the commitment from the AQUILA Network members, 26 Laboratories plus the European Reference Laboratory for Air Pollution deployed their instruments at a single place in the premises of the Joint Research Centre in Ispra (Italy) during the same period of time (18 Januar - 14 March 2018). 28 samplers and one automatic analyser for PM10 and 23 samplers and one automatic analyser for PM2.5 collected ambient aerosol samples. Gravimetric analyses of the filters before and after sampling were performed by the participants in their own laboratories following their own conditioning and filter handling procedures. The assigned daily values for PM10 and PM2.5 were calculated as the robust average of all participants. They ranged from 5.8 to 76.6 μg/m³ for PM10, and from 4.8 to 69.2 μg/m³ for PM2.5. The scope of this inter-laboratory comparison was to assess the robustness of the measurement process and to determine the performance of the participants' procedures. From the statistical analyses, conclusions on the performance of the method could also be drawn. The reproducibility of the method was 11% for both PM10 and PM2.5. After excluding blunders, for PM10, out of 1470 reported daily values, 38 (2.6%) were found to be unsatisfactory with respect to the z'-score criterion ( z' ≥3). For PM2.5, out of 1203 daily averages, only 8 (0.7%) showed an unsatisfactory result. Questionable results (3> z' >2) amounted 2.8% and 5.7% of all PM10 and PM2.5 data, respectively. The En-score, which takes into account also the uncertainties reported by the participants, exceeded the critical threshold ( En ≥1) for 6.3% and 9.3% of the PM10 and PM2.5 reported data, respectively. The overall results of the ILC show a similar performance as in 2015, which suggests that the measurement procedures have already reached a rather high level of quality.