Abstract
A reference material of a PM2.5-like atmospheric dust material has been prepared using a newly developed method. It is intended to certify values for the mass fraction of SO42−, NO3−, Cl− (anions) and Na+, K+, NH4+, Ca2+, Mg2+ (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 PM10-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 PM2.5-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 PM2.5-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 PM2.5 collected on filters. The method described here is a relatively rapid means to obtain large quantities of PM2.5. With access to smaller freeze dryers, still 5 to 10 g per freeze-drying cycle can be obtained. Access to such quantities of PM2.5-like material could potentially be used for different kinds of experiments when performing research in this field.Graphical abstractThe 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 PM2,5. The high material yield in a relatively short time is a distinct advantage in comparison with collection of air-sampled PM2,5
Highlights
The contamination of ambient air by airborne dust, so-called PM10 and PM2.5, is a major problem in many densely populated parts of the world [1]
For the purpose of producing a certified reference material (CRM) by a collection of naturally occurring PM2.5, an approach was described by Heller-Zeisler et al using collections on filters by suspending ambient particulate matter in ultra-pure water [13]
A substantial amount of a sufficiently homogeneous PM2.5like reference material has been produced from ambient dust and filled in vials
Summary
The contamination of ambient air by airborne dust, so-called PM10 and PM2.5, is a major problem in many densely populated parts of the world [1]. There are unspecified sources [2] These particles are known to cause premature deaths and respiratory problems among the general population, especially in heavily contaminated areas [3]. In this context, the PM2.5 particles are notoriously dangerous as they can penetrate deep into the lungs and may even pass into the bloodstream [3, 4]. The legislation addresses the need to assess natural background levels of particles in rural areas for subtraction from the total particle load. The reference material described in this work addresses the latter aspect
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