Automated and correlative SEM-EDX-Raman particle analysis on fine dust filters of extreme events: New Year’s Eve and Sahara dust

Various natural or manmade events can have major impacts on the local and nationwide airquality. This includes Sahara dust events and fireworks during New Year´s Eve nights, where highfine dust concentrations are registered. To obtain information about the presence of the differentelements and materials in particulate matter (PM) in the air, various qualitative and quantitativemethods are available. In this study scanning electron microscopy (SEM) combined with energydispersive spectroscopy (EDX) and Raman spectroscopy were used to analyse PM at fine dustfilters. Although quantifying the element concentration via EDX is not permissible in this particlesize fraction, the composition of each individual particle can still be revealed.To enable this, absolute filters tapes (AFT) were investigated in a correlative microscope. Thesefilters are standardly used in air quality monitoring to measure the fine dust concentration atvarious sites on an hourly basis. To obtain initially a good spatial resolution in the used SEM(Zeiss, Sigma 300 VP), the electrically non-conductive filter was coated by carbon evaporation.Three of the recorded samples are shown in this abstract, while several thousand of particles areautomated recorded each: New Year’s Eve 2017/18, New Year’s Eve 2020/21 and ameasurement at the night 23th of December 2020. The weather propagation conditions of thethree nights are comparable as always an atmospheric inversion and a comparable windspeedprevailed [1]. Figure 1 shows the comparison of the fine dust concentration at both New Year’sEve nights. It can clearly be seen that the fine dust pollution of New Year’s Eve 2017/18 is aboutten times higher than 2020/21. The comparison of a few selected elements shows, that someconcentrations are significantly higher at the Silvester nights, e.g. Pb, Sr or Bi, while others like Fecan be counted to the background elements.Subsequent correlative Raman spectroscopy investigations of particular particles are planned.Therefore, the samples have to be investigated in the available low vacuum mode of the usedRISE (Raman imaging and scanning electron microscopy) System [2]. This should give acomprehensive insight into the toxicity of particles in the air during such events.