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Volume 9, issue 6
Atmos. Meas. Tech., 9, 2735–2752, 2016
https://doi.org/10.5194/amt-9-2735-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Meas. Tech., 9, 2735–2752, 2016
https://doi.org/10.5194/amt-9-2735-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 01 Jul 2016

Research article | 01 Jul 2016

A high-resolution time-of-flight chemical ionization mass spectrometer utilizing hydronium ions (H3O+ ToF-CIMS) for measurements of volatile organic compounds in the atmosphere

Bin Yuan1,2, Abigail Koss1,2,3, Carsten Warneke1,2, Jessica B. Gilman1, Brian M. Lerner1,2, Harald Stark2,3,4, and Joost A. de Gouw1,2,3 Bin Yuan et al.
  • 1NOAA Earth System Research Laboratory (ESRL), Chemical Sciences Division, Boulder, CO, USA
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, CO, USA
  • 3Department of Chemistry and Biochemistry, University of Colorado at Boulder, CO, USA
  • 4Aerodyne Research Inc., Billerica, MA 01821, USA

Abstract. Proton transfer reactions between hydronium ions (H3O+) and volatile organic compounds (VOCs) provide a fast and highly sensitive technique for VOC measurements, leading to extensive use of proton-transfer-reaction mass spectrometry (PTR-MS) in atmospheric research. Based on the same ionization approach, we describe the development of a high-resolution time-of-flight chemical ionization mass spectrometer (ToF-CIMS) utilizing H3O+ as the reagent ion. The new H3O+ ToF-CIMS has sensitivities of 100–1000 cps ppb−1 (ion counts per second per part-per-billion mixing ratio of VOC) and detection limits of 20–600 ppt at 3σ for a 1 s integration time for simultaneous measurements of many VOC species of atmospheric relevance. The ToF analyzer with mass resolution (m∕Δm) of up to 6000 allows the separation of isobaric masses, as shown in previous studies using similar ToF-MS. While radio frequency (RF)-only quadrupole ion guides provide better overall ion transmission than ion lens system, low-mass cutoff of RF-only quadrupole causes H3O+ ions to be transmitted less efficiently than heavier masses, which leads to unusual humidity dependence of reagent ions and difficulty obtaining a humidity-independent parameter for normalization. The humidity dependence of the instrument was characterized for various VOC species and the behaviors for different species can be explained by compound-specific properties that affect the ion chemistry (e.g., proton affinity and dipole moment). The new H3O+ ToF-CIMS was successfully deployed on the NOAA WP-3D research aircraft for the SONGNEX campaign in spring of 2015. The measured mixing ratios of several aromatics from the H3O+ ToF-CIMS agreed within ±10 % with independent gas chromatography measurements from whole air samples. Initial results from the SONGNEX measurements demonstrate that the H3O+ ToF-CIMS data set will be valuable for the identification and characterization of emissions from various sources, investigation of secondary formation of many photochemical organic products and therefore the chemical evolution of gas-phase organic carbon in the atmosphere.

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We present the development of a hydronium (H3O+) time of flight chemical ionization mass spectrometer (H3O+ ToF-CIMS). We characterize the humidity dependence of the reagent ions and VOC signals in details. The low mass cutoff issue of RF-only quadrupole leads to unusual humidity dependence of reagent ions. The new H3O+ ToF-CIMS was successfully deployed on the NOAA WP-3D research aircraft for the SONGNEX campaign in 2015 and some initial results from the SONGNEX campaign are presented.
We present the development of a hydronium (H3O+) time of flight chemical ionization mass...
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