11 May 2022
11 May 2022
Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).

Temperature dependent sensitivity of iodide chemical ionization mass spectrometers

Michael A. Robinson1,2,3, J. Andrew Neuman1,2, L. Gregory Huey4, James M. Roberts1, Steven S. Brown1,3, and Patrick R. Veres1 Michael A. Robinson et al.
  • 1NOAA Chemical Sciences Laboratory, Boulder, Colorado, USA
  • 2Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder, Boulder, Colorado, USA
  • 3Department of Chemistry, University of Colorado Boulder, Boulder, Colorado, USA
  • 4School of Earth and Atmospheric Science, Georgia Institute of Technology, Atlanta, GA, USA

Abstract. Iodide chemical ionization mass spectrometry (CIMS) is a common analytical tool used in both laboratory and field experiments to measure a large suite of atmospherically relevant compounds. Here, we describe a systematic ion molecule reactor (IMR) temperature dependence of iodide CIMS analyte sensitivity for a wide range of analytes in laboratory experiments. Weakly bound iodide clusters such as HCl, HONO, HCOOH, HCN, phenol, 2-nitrophenol and acyl peroxy nitrate (PAN) detected via the peroxy radical cluster, all exhibit strong IMR temperature dependence of sensitivity ranging from -3.4 to 5.9 % °C-1 (from 37 to 47 °C). Strongly bound iodide clusters such as Br2, N2O5, ClNO2, and PAN detected via the carboxylate anion all exhibit little to no IMR temperature dependence ranging from 0.2 to -0.9 % °C-1 (from 37 to 47 °C). The IMR temperature relationships of weakly bound clusters provide an estimate of net reaction enthalpy and comparison with database values, indicating these clusters are in thermal equilibrium. Ground site HCOOH data collected in the summer of 2021 in Pasadena, CA are corrected showing a reversal in the diel cycle, emphasizing the importance of this correction (35 ± 6 % during the day, -26 ± 2 % at night). Finally, we recommend two approaches to minimizing this effect in the field, namely heating or cooling the IMR; the latter has the added benefit of improving absolute sensitivity and reducing drift in harsh field environments.

Michael A. Robinson et al.

Status: open (until 16 Jun 2022)

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Michael A. Robinson et al.

Michael A. Robinson et al.


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Short summary
Iodide chemical ionization mass spectrometers (CIMS) are commonly used in atmospheric chemistry laboratory studies and field campaigns. Deployment of the NOAA iodide CIMS in the summer of 2021 indicated a significant and overlooked temperature dependence of instrument sensitivity. This work explores the analytes influenced by this phenomena. Additionally, we recommend controls to reduce this influence for field deployments in the future.