Preprints
https://doi.org/10.5194/amt-2021-327
https://doi.org/10.5194/amt-2021-327

  24 Nov 2021

24 Nov 2021

Review status: this preprint is currently under review for the journal AMT.

Substantial organic impurities at the surface of synthetic ammonium sulfate particles

Junteng Wu1, Nicolas Brun1, Juan Miguel González-Sánchez1, Badr R’Mili1, Brice Temime Roussel1, Sylvain Ravier1, Jean-Louis Clément2, and Anne Monod1 Junteng Wu et al.
  • 1Aix Marseille Univ, CNRS, LCE, Marseille, France
  • 2Aix Marseille Univ, CNRS, ICR, Marseille, France

Abstract. Ammonium sulfate (AS) particles are widely used for studying the physical-chemistry processes of aerosols and for instrument calibrations. Small quantities of organic matter can greatly influence the studied properties, as observed by many laboratory studies. In this work, monodisperse particles (from 200 nm to 500 nm) were generated by nebulizing various AS solutions and organic impurities were quantified relative to sulfate using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). The organic content found in AS solutions was also tentatively identified using a Liquid Chromatography–tandem Mass Spectrometry (LC-MS). The results from both analytical techniques were consistent and demonstrated that the organic impurities contained oxygen, nitrogen and/or sulfur, their molecular masses ranged from m/z 69 to 420, they likely originate from the commercial AS crystals. For AS particle sizes ranging from 200 nm to 500 nm, the total mass fraction of organic (relative to sulfate) ranged from 3.8 % to 1.5 % respectively. An inorganic-organic mixture model suggested that the organic impurities were coated on the AS particle surface with a density of 1.1 × 10−3 g m−2. A series of tests were performed to remove the organic content (using pure N2 in the flow, ultrapure water in the solutions, and very high AS quality), showing that at least 40 % of the organic impurities could be removed. In conclusion, it is recommended to use AS seeds with caution, especially when small particles are used, in terms of AS purity and water purity when aqueous solutions are used for atomization.

Junteng Wu et al.

Status: open (until 30 Dec 2021)

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Junteng Wu et al.

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Short summary
This work quantified and tentatively identified the organic impurities on ammonium sulfate aerosols generated in the laboratory. They are likely low volatile and high mass molecules containing oxygen, nitrogen and/or sulfur. Our results show that these organic impurities likely originate from the commercial AS crystals. It is recommended to use AS seeds with caution, especially when small particles are used, in terms of AS purity and water purity when aqueous solutions are used for atomization.