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

A reference material of a PM-like atmospheric dust material has been prepared using a newly developed method. It is intended to certify values for the mass fraction of SO, NO, Cl (anions) and Na, K, NH, Ca, Mg (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-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-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-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 collected on filters. The method described here is a relatively rapid means to obtain large quantities of PM. With access to smaller freeze dryers, still 5 to 10 g per freeze-drying cycle can be obtained. Access to such quantities of PM-like material could potentially be used for different kinds of experiments when performing research in this field. Graphical abstract The novelty of the method lies in transformation of a suspension with fine particulate matter to a homogeneous and stable powder with characteristics similar to air-sampled PM. The high material yield in a relatively short time is a distinct advantage in comparison with collection of air-sampled PM.