Studying the Fate of Non-Volatile Organic Compounds in a Commercial Plasma Air Purifier



Stefan Schmid1, Cornelia Seiler2, Andreas C. Gerecke2, Herbert Hächler3, Hubert Hilbi4, Joachim Frey5, Simon Weidmann1, Lukas Meier1, Christian Berchtold1, and Renato Zenobi1


  1. ETH Zürich, Department of Chemistry and Applied Biosciences, CH-8093 Zürich, Switzerland
  2. Swiss Federal Laboratories for Material Science and Technology (EMPA), CH-8600 Dübendorf, Switzerland
  3. University of Zürich, Institute for Food Safety and Hygiene, National Centre for Enteropathogenic Bacteria and Listeria (NENT), CH-8057 Zürich, Switzerland
  4. Ludwig-Maximilians-Universität München Max von Pettenkofer-Institut, D-80336 München, Germany
  5. University of Bern, Institute for Veterinary Bacteriology, CH-3001 Bern, Switzerland


Degradation of non-volatile organic compounds–environmental toxins (methyltriclosane and phenanthrene), bovine serum albumin, as well as bioparticles (Legionella pneumophila, Bacillus subtilis, and Bacillus anthracis)–in a commercially available plasma air purifier based on a cold plasma was studied in detail, focusing on its efficiency and on the resulting degradation products. This system is capable of handling air flow velocities of up to 3.0 m s−1 (3200 L min−1), much higher than other plasma-based reactors described in the literature, which generally are limited to air flow rates below 10 L min−1. Mass balance studies consistently indicated a reduction in concentration of the compounds/particles after passage through the plasma air purifier, 31% for phenanthrene, 17% for methyltriclosane, and 80% for bovine serum albumin. L. pneumophila did not survive passage through the plasma air purifier, and cell counts of aerosolized spores of B. subtilis and B. anthracis were reduced by 26- and 15-fold, depending on whether it was run at 10 Hz or 50 Hz, respectively. However rather than chemical degradation, deposition on the inner surfaces of the plasma air purifier occured. Our interpretation is that putative “degradation” efficiencies were largely due to electrostatic precipitation rather than to decomposition into smaller molecules.

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As part of an experiment created to study the degradation of non-volatile organic compounds in a plasma air purifier (PAP), MALDI mass spectrometry was used to analyze samples including methyltriclosane, phenanthrene and bovine serum albumin (BSA).

54.3 mg of methyltriclosane and phenanthrene were each dissolved separately in 1200 μL of benzene before being injected at least twice into nebulization surface of the PAP so that the exhaust could be sampled and observed signals were identified using mass spectrometry.

10 mL of a 10 mg mL-1 aqueous BSA solution was fed into the nebulization surface with a constant sample flow rate of 375 μL min-1. Exhaust from the PAP was sampled by bubbling 10% of the whole air flow through water using an 80 mL impinger. 50 mL of the sample was transferred into a falcon tube before HPLC was performed. The analysis included the extraction of BSA that was trapped in the copper electrodes of the PAP. The electrodes were placed in a beaker filled with 1 L of water and submerged for 5 minutes to dissolve any deposited BSA. The water was reduced to 50 mL in a round bottom flask and MALDI mass spectrometry was performed using a commercial mass spectrometer that had been modified with a CovalX HM2 detection system.



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