Chemical ionization mass spectrometry utilizing ammonium ions (NH₄⁺ CIMS) for measurements of organic compounds in the atmosphere
- Creators
-
Xu, Lu1, 2
-
Coggon, Matthew M.2
-
Stockwell, Chelsea E.1, 2
-
Gilman, Jessica B.2
-
Robinson, Michael A.1, 2, 3
-
Breitenlechner, Martin1, 2
-
Lamplugh, Aaron1, 2, 3
-
Crounse, John D.4
-
Wennberg, Paul O.4
-
Neuman, J. Andrew1, 2
-
Novak, Gordon A.1, 2
-
Veres, Patrick R.2
-
Brown, Steven S.2, 3
-
Warneke, Carsten2
Abstract
We describe the characterization and field deployment of chemical ionization mass spectrometry (CIMS) using a recently developed focusing ion-molecule reactor (FIMR) and ammonium–water cluster (NH₄⁺⋅H₂O) as the reagent ion (denoted as NH₄⁺ CIMS). We show that NH₄⁺⋅H₂O is a highly versatile reagent ion for measurements of a wide range of oxygenated organic compounds. The major product ion is the cluster with NH₄⁺ produced via ligand-switching reactions. Other product ions (e.g., protonated ion, cluster ion with NH₄⁺⋅H₂O, with H₃O+, and with H₃O+⋅H₂O) are also produced, but with minor fractions for most of the oxygenated compounds studied here. The instrument sensitivities (ion counts per second per part per billion by volume, cps ppbv−1) and product distributions are strongly dependent on the instrument operating conditions, including the ratio of ammonia (NH₃) and H₂O flows and the drift voltages, which should be carefully selected to ensure NH₄⁺⋅H₂O as the predominant reagent ion and to optimize sensitivities. For monofunctional analytes, the NH₄⁺⋅H₂O chemistry exhibits high sensitivity (i.e., >1000 cps ppbv−1) to ketones, moderate sensitivity (i.e., between 100 and 1000 cps ppbv−1) to aldehydes, alcohols, organic acids, and monoterpenes, low sensitivity (i.e., between 10 and 100 cps ppbv−1) to isoprene and C1 and C2 organics, and negligible sensitivity (i.e., <10 cps ppbv−1) to reduced aromatics. The instrumental sensitivities of analytes depend on the binding energy of the analyte–NH₄⁺ cluster, which can be estimated using voltage scanning. This offers the possibility to constrain the sensitivity of analytes for which no calibration standards exist. This instrument was deployed in the RECAP campaign (Re-Evaluating the Chemistry of Air Pollutants in California) in Pasadena, California, during summer 2021. Measurement comparisons against co-located mass spectrometers show that the NH₄⁺ CIMS is capable of detecting compounds from a wide range of chemical classes. The NH₄⁺ CIMS is valuable for quantification of oxygenated volatile organic compounds (VOCs) and is complementary to existing chemical ionization schemes.
Copyright and License
© Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 License.
Published by Copernicus Publications on behalf of the European Geosciences Union.
Acknowledgement
We thank the Caltech Facilities for their support in the RECAP campaign. We thank Kristian H. Møller and Henrik G. Kjaergaard for calculation of dipole moments and polarizabilities.
Funding
This work was supported by the NOAA cooperative agreement with CIRES (agreement no. NA17OAR4320101). The NOAA Chemical Sciences Laboratory acknowledges support for this work from the California Air Resources Board (agreement no. 20RD002).
Contributions
LX and CW designed the research, LX operated the NH₄⁺ CIMS, MMC and CES operated the H3O+ CIMS, JBG and AL operated the GC-MS, JDC and POW operated the CF3O− CIMS, MAR, JAN, PRV, GAN, MMC, CES, and SSB provided critical support and comments in NH₄⁺ CIMS operation, and KHM performed theoretical calculations. All authors commented on the paper.
Data Availability
Data from the RECAP campaign are available to the general public at https://csl.noaa.gov/groups/csl7/measurements/2021sunvex/GroundLA/DataDownload/ (last access: 10 December 2022). The NOAA CSL Tropospheric Chemistry Group data archive for the RECAP campaign is created and maintained by Kenneth Aikin.
Supplemental Material
The supplement related to this article is available online at: https://doi.org/10.5194/amt-15-7353-2022-supplement.
Additional Information
This paper was edited by Anna Novelli and reviewed by two anonymous referees.
Files
Name | Size | Download all |
---|---|---|
md5:b740c2c91235f2f58e09b37d21a106e9
|
5.9 MB | Preview Download |
md5:788f36dcc29a18d84e934b8d141e1081
|
2.8 MB | Preview Download |
Additional details
- National Oceanic and Atmospheric Administration
- NA17OAR4320101
- California Air Resources Board
- 20RD002
- Accepted
-
2022-11-19Accepted
- Caltech groups
- Division of Geological and Planetary Sciences
- Publication Status
- Published