Preparation of a PM(2.5)-like reference material in sufficient quantities for accurate monitoring of anions and cations in fine atmospheric dust

A reference material of a PM(2.5)-like atmospheric dust material has been prepared using a newly developed method. It is intended to certify values for the mass fraction of SO(4) (2−), NO(3) (−), Cl(−) (anions) and Na(+), K(+), NH(4) (+), Ca(2+), Mg(2+) (cations) in this material. A successful route for the preparation of the candidate reference material is described alongside with two alternative approaches that were abandoned. First, a PM(10)-like suspension was allowed to stand for 72 h. Next, 90% of the volume was siphoned off. The suspension was spiked with appropriate levels of the desired ions just prior to drop-wise shock-freezing in liquid nitrogen. Finally, freeze drying of the resulting ice kernels took place. In using this approach, it was possible to produce about 500 g of PM(2.5)-like material with appropriate characteristics. Fine dust in 150-mg portions was filled into vials under an inert atmosphere. The final candidate material approaches the EN12341 standard of a PM(2.5)-material containing the ions mentioned in Directive 2008/50/EC of the European Union. The material should be analysed using the CEN/TR 16269:2011 method for anions and cations in PM(2.5) collected on filters. The method described here is a relatively rapid means to obtain large quantities of PM(2.5). With access to smaller freeze dryers, still 5 to 10 g per freeze-drying cycle can be obtained. Access to such quantities of PM(2.5)-like material could potentially be used for different kinds of experiments when performing research in this field. [Figure: see text]