Preprints
https://doi.org/10.5194/amt-2021-330
https://doi.org/10.5194/amt-2021-330

  14 Oct 2021

14 Oct 2021

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

A Versatile Vacuum Ultraviolet Ion Source for Reduced Pressure Bipolar Chemical Ionization Mass Spectrometry

Martin Breitenlechner1,2, Gordon A. Novak1,2, J. Andrew Neuman1,2, Andrew W. Rollins1, and Patrick R. Veres1 Martin Breitenlechner et al.
  • 1NOAA Chemical Science Laboratory (CSL), 325 Broadway, Boulder, Colorado 80305, USA
  • 2Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder, Boulder, Colorado 80309, USA

Abstract. We present the development of a Chemical Ionization Mass Spectrometer (CIMS) ion source specifically designed for in situ measurements of trace gases in the upper troposphere and lower stratosphere. The ion source utilizes a commercially available photoionization krypton lamp, primarily emitting photons in the vacuum ultraviolet (VUV) region at wavelengths of 124 and 117 nm (corresponding to energies of 10 and 10.6 eV, respectively), coupled to a commercially available Vocus Proton Transfer Reaction Mass Spectrometer. The VUV ion source can produce both negative and positive reagent ions, however, here we primarily focus on generating iodide anions (I). The instrument’s drift tube (also known as ion molecule reactor) operates at pressures between 2 and 10 mbar, which facilitates ambient sampling at atmospheric pressures as low as 50 mbar. The low operating pressure reduces secondary ion chemistry that can occur in iodide CIMS. It also allows the addition of water vapor to the drift tube to exceed typical ambient humidity by more than one order of magnitude, significantly reducing ambient humidity dependence of sensitivities. An additional benefit of this ion source and drift tube is a 10 to 100-fold reduction in nitrogen consumed during operation relative to standard I ion sources, resulting in significantly reduced instrument weight and operational costs. In iodide mode, sensitivities of 76 cps/ppt for nitric acid, 35 cps/ppt for Br2, and 8.9 cps/ppt for Cl2 were achieved. Lastly, we demonstrate that this ion source can generate benzene (C6H6+) and ammonium (NH4+) reagent ions to expand the number of detected atmospheric trace gases.

Martin Breitenlechner et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-330', Anonymous Referee #1, 22 Nov 2021
  • RC2: 'Comment on amt-2021-330', Anonymous Referee #2, 22 Nov 2021

Martin Breitenlechner et al.

Martin Breitenlechner et al.

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Short summary
We coupled a new ion source to a commercially available state-of-the-art trace gas analyzer. The instrument is particularly well suited for conducting high altitude observations, addressing the challenges of low ambient pressures and a complex sample matrix. The new instrument and ion source provides significant advantages to more traditional modes of operation, without sacrificing the sensitivity and flexibility of this technique.