Cascade filter system tests for airborne nano‐ and microplastic particle analytics in a laboratory dust chamber

Abstract

AbstractMeasuring nano‐ and microplastic particle (NMP) loads in air requires suitable analytical filter systems that allow a size‐selective separation of airborne nano‐ and microplastic (NMP) fractions. Previously, various filter materials and setups including nano/micro cascade filtration stacks have been presented (P.‐T. Miclea, 2022). To evaluate these novel filter systems, implementing reliable sampling procedures and instrumentation, as well as sample handling, well‐defined test setups, NMP reference materials, and procedures are of major interest. In this study, a novel triple‐stage silicon (Si) and aluminum oxide (Al2O3) cascade filter system for airborne NMP particles is tested in a laboratory environment. Special focus is put on its ability for size‐selective analytical filtration of airborne NMP particles based on a well‐defined mixture of poly‐ and monodisperse NMP reference materials. For this purpose, a laboratory dust test chamber has been adapted for the dispersion of NMP particles in air as well as the vacuum air extraction through the cascade filter system. A defined NMP test material was fabricated from polydisperse polyethylene (PE) and PE terephthalate, and monodisperse polystyrene, polymethylmethacrylate, spanning a size region from 130 nm to >22 µm. Dispersion and filtration experiments are performed by vacuum extraction under defined temperature, pressure, and humidity conditions on single and triple filtration stages. NMP particle analytics are performed with polydisperse PE particles on a single‐stage filter system with subsequent optical microscopy. Here, the aim is to detect the filtration cutoff for retained particles and transmitted particles referring to initial distribution. A second experiment is run on a triple filtration cascade with mixed poly‐ and monodisperse NMP test material. The different filter stages are equipped with analytical Si and Al2O3 filters with pore sizes of 10 µm, 1 µm, and 100 nm, to test the size selectivity and sealing of the complete cascade setup. The NMP particle size distribution on the individual analytical filter substrates is analyzed by optical and scanning electron microscopy to assess size selectivity performance of the triple‐stage setup. The obtained results in our laboratory NMP dust‐dispersion test chamber demonstrate requirements and limitation of size‐selective NMP cascade filter systems and the involved analytical procedures. Future applications in real indoor and outdoor environments will be discussed.