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

2021 ◽  
Author(s):  
Martin Breitenlechner ◽  
Gordon A. Novak ◽  
J. Andrew Neuman ◽  
Andrew W. Rollins ◽  
Patrick R. Veres
Keyword(s):  
Mass Spectrometer ◽  
Drift Tube ◽  
Chemical Ionization ◽  
Vacuum Ultraviolet ◽  
Trace Gases ◽  
Ion Source ◽  
Ionization Mass ◽  
Operating Pressure ◽  
Reduced Pressure ◽  
Ambient Humidity

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.

scholarly journals The airborne mass spectrometer AIMS – Part 2: Measurements of trace gases with stratospheric or tropospheric origin in the UTLS

2015 ◽  
Vol 8 (12) ◽  
pp. 13567-13607 ◽  
Author(s):  
T. Jurkat ◽  
S. Kaufmann ◽  
C. Voigt ◽  
D. Schäuble ◽  
P. Jeßberger ◽  
...  
Keyword(s):  
Nitrogen Oxide ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Trace Gases ◽  
Measurement Techniques ◽  
Ion Source ◽  
Trace Gas ◽  
Ionization Mass ◽  
Custom Made ◽  
Gas Measurements

Abstract. Understanding the role of climate-sensitive trace gas variabilities in the upper troposphere and lower stratosphere region (UTLS) and their impact on its radiative budget requires accurate measurements. The composition of the UTLS is governed by transport and chemistry of stratospheric and tropospheric constituents, such as chlorine, nitrogen oxide and sulphur components. The Airborne chemical Ionization Mass Spectrometer AIMS has been developed to accurately measure a set of these constituents on aircraft by means of chemical ionization. Here we present a setup using chemical ionization with SF5− reagent ions for the simultaneous measurement of trace gas concentrations in the pptv to ppmv (10−12 to 10−6 mol mol−1) range of HCl, HNO3 and SO2 with in-flight and online calibration called AIMS-TG. Part 1 of this paper (Kaufmann et al., 2015) reports on the UTLS water vapour measurements with the AIMS-H2O configuration. The instrument can be flexibly switched between two configurations depending on the scientific objective of the mission. For AIMS-TG, a custom-made gas discharge ion source has been developed generating a characteristic ionization scheme. HNO3 and HCl are routinely calibrated in-flight using permeation devices, SO2 is permanently calibrated during flight adding an isotopically labelled 34SO2 standard. In addition, we report on trace gas measurements of HONO which is sensitive to the reaction with SF5−. The detection limit for the various trace gases is in the low ten pptv range at a 1 s time resolution with an overall uncertainty of the measurement in the order of 20 %. AIMS has been integrated and successfully operated on the DLR research aircraft Falcon and HALO. Exemplarily, measurements conducted during the TACTS/ESMVal mission with HALO in 2012 are presented, focusing on a classification of tropospheric and stratospheric influences in the UTLS region. Comparison of AIMS measurements with other measurement techniques allow to draw a comprehensive picture of the sulphur, chlorine and reactive nitrogen oxide budget in the UTLS. The combination of the trace gases measured with AIMS exhibit the potential to gain a better understanding of the trace gas origin and variability at and near the tropopause.

scholarly journals The airborne mass spectrometer AIMS – Part 2: Measurements of trace gases with stratospheric or tropospheric origin in the UTLS

2016 ◽  
Vol 9 (4) ◽  
pp. 1907-1923 ◽  
Author(s):  
Tina Jurkat ◽  
Stefan Kaufmann ◽  
Christiane Voigt ◽  
Dominik Schäuble ◽  
Philipp Jeßberger ◽  
...  
Keyword(s):  
Nitrogen Oxide ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Trace Gases ◽  
Measurement Techniques ◽  
Ion Source ◽  
Trace Gas ◽  
Ionization Mass ◽  
Custom Made ◽  
Research Aircraft

Abstract. Understanding the role of climate-sensitive trace gas variabilities in the upper troposphere and lower stratosphere region (UTLS) and their impact on its radiative budget requires accurate measurements. The composition of the UTLS is governed by transport and chemistry of stratospheric and tropospheric constituents, such as chlorine, nitrogen oxide and sulfur compounds. The Atmospheric chemical Ionization Mass Spectrometer AIMS has been developed to accurately measure a set of these constituents on aircraft by means of chemical ionization. Here we present a setup using SF5− reagent ions for the simultaneous measurement of trace gas concentrations of HCl, HNO3 and SO2 in the  pptv to ppmv (10−12 to 10−6 mol mol−1) range with in-flight and online calibration called AIMS-TG (Atmospheric chemical Ionization Mass Spectrometer for measurements of trace gases). Part 1 of this paper (Kaufmann et al., 2016) reports on the UTLS water vapor measurements with the AIMS-H2O configuration. The instrument can be flexibly switched between two configurations depending on the scientific objective of the mission. For AIMS-TG, a custom-made gas discharge ion source has been developed for generation of reagent ions that selectively react with HCl, HNO3, SO2 and HONO. HNO3 and HCl are routinely calibrated in-flight using permeation devices; SO2 is continuously calibrated during flight adding an isotopically labeled 34SO2 standard. In addition, we report on trace gas measurements of HONO, which is sensitive to the reaction with SF5−. The detection limit for the various trace gases is in the low 10 pptv range at a 1 s time resolution with an overall uncertainty of the measurement of the order of 20 %. AIMS has been integrated and successfully operated on the DLR research aircraft Falcon and HALO (High Altitude LOng range research aircraft). As an example, measurements conducted during the TACTS/ESMVal (Transport and Composition of the LMS/UT and Earth System Model Validation) mission with HALO in 2012 are presented, focusing on a classification of tropospheric and stratospheric influences in the UTLS region. The combination of AIMS measurements with other measurement techniques yields a comprehensive picture of the sulfur, chlorine and reactive nitrogen oxide budget in the UTLS. The different trace gases measured with AIMS exhibit the potential to gain a better understanding of the trace gas origin and variability at and near the tropopause.

scholarly journals A Vacuum Ultraviolet Ion Source (VUV-IS) for Iodide-Chemical Ionization Mass Spectrometry: A Substitute for Radioactive Ion Sources

2020 ◽  
Author(s):  
Yi Ji ◽  
L. Gregory Huey ◽  
David J. Tanner ◽  
Young Ro Lee ◽  
Patrick R. Veres ◽  
...  
Keyword(s):  
Formic Acid ◽  
Methyl Iodide ◽  
Chemical Ionization ◽  
Vacuum Ultraviolet ◽  
Ambient Air ◽  
Radioactive Source ◽  
Ion Source ◽  
Ion Sources ◽  
Ionization Mass ◽  
Molecular Chlorine

Abstract. A new ion source (IS) utilizing vacuum ultraviolet (VUV) light is developed and characterized for use with iodide-chemical ionization mass spectrometers (I−-CIMS). The VUV-IS utilizes a compact krypton lamp that emits light in two wavelength bands corresponding to energies of ~10.0 and 10.6 eV. The VUV light photoionizes either methyl iodide (ionization potential, IP = 9.54 ± 0.02 eV) or benzene (IP = 9.24378 ± 0.00007 eV) to form cations and photoelectrons. The electrons react with methyl iodide to form I− which serves as the reagent ion for the CIMS. The VUV-IS is characterized by measuring the sensitivity of a quadrupole CIMS (Q-CIMS) to formic acid, molecular chlorine, and nitryl chloride under a variety of flow and pressure conditions. The sensitivity of the Q-CIMS, with the VUV-IS, reached up to ~700 Hz pptv−1, with detection limits of less than 1 pptv for a one minute integration period. The reliability of the Q-CIMS with a VUV-IS is demonstrated with data from a month long ground-based field campaign. The VUV-IS is further tested by operation on a high resolution time-of-flight CIMS (TOF-CIMS). Sensitivities greater than 25 Hz pptv−1 were obtained for formic acid and molecular chlorine, which were similar to that obtained with a radioactive source. In addition, the mass spectra from sampling ambient air was cleaner with the VUV-IS on the TOF-CIMS compared to measurements using a radioactive source. These results demonstrate that the VUV lamp is a viable substitute for radioactive ion sources on I−-CIMS systems for most applications. In addition, the VUV-IS can likely be extended to other reagent ions, such as SF6− which are formed from high IP electron attachers, by the use of absorbers such as benzene to serve as a source of photoelectrons.

scholarly journals A switchable reagent ion high resolution time-of-flight chemical ionization mass spectrometer for real-time measurement of gas phase oxidized species: characterization from the 2013 Southern Oxidant and Aerosol Study

2015 ◽  
Vol 8 (3) ◽  
pp. 3199-3244 ◽  
Author(s):  
P. Brophy ◽  
D. K. Farmer
Keyword(s):  
High Resolution ◽  
Formic Acid ◽  
Gas Phase ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Time Of Flight ◽  
Ionization Mass ◽  
Resolution Time ◽  
Limit Of Quantification ◽  
Reduced Pressure

Abstract. A novel configuration of the Aerodyne high resolution time-of-flight chemical ionization mass spectrometer (HR-TOF-CIMS) as a switchable reagent ion (SRI) HR-TOF-CIMS is presented and described along with data collected at the Southern Oxidant and Aerosol Study (SOAS) during the summer of 2013. The calibration system and reduced pressure gas-phase inlet are characterized. The average limit of detection and limit of quantification for formic acid during SOAS are 82 and 863 ppt, respectively, corresponding to an average sensitivity of 13 ± 5 Hz ppt−1. Hourly background determinations and calibrations are shown to be essential for tracking instrument performance and accurately quantifying formic acid. Maximum daytime formic acid concentrations of 10 ppb are reported during SOAS, and a strong diel cycle is observed leading to night time concentrations below the limit of quantification. Other species presented exhibit diel behavior similar to formic acid. The concept of the mass defect enhancement plot and the use of signal-to-noise are described in detail as a method for investigating HR-TOF-CIMS spectra in an effort to reduce data complexity.

scholarly journals A vacuum ultraviolet ion source (VUV-IS) for iodide–chemical ionization mass spectrometry: a substitute for radioactive ion sources

2020 ◽  
Vol 13 (7) ◽  
pp. 3683-3696
Author(s):  
Yi Ji ◽  
L. Gregory Huey ◽  
David J. Tanner ◽  
Young Ro Lee ◽  
Patrick R. Veres ◽  
...  
Keyword(s):  
Formic Acid ◽  
Methyl Iodide ◽  
Chemical Ionization ◽  
Vacuum Ultraviolet ◽  
Ambient Air ◽  
Radioactive Source ◽  
Ion Source ◽  
Ion Sources ◽  
Ionization Mass ◽  
Molecular Chlorine

Abstract. A new ion source (IS) utilizing vacuum ultraviolet (VUV) light is developed and characterized for use with iodide–chemical ionization mass spectrometers (I−-CIMS). The VUV-IS utilizes a compact krypton lamp that emits light at two wavelengths corresponding to energies of ∼10.030 and 10.641 eV. The VUV light photoionizes either methyl iodide (ionization potential, IP = 9.54 ± 0.02 eV) or benzene (IP = 9.24378 ± 0.00007 eV) to form cations and photoelectrons. The electrons react with methyl iodide to form I−, which serves as the reagent ion for the CIMS. The VUV-IS is characterized by measuring the sensitivity of a quadrupole CIMS (Q-CIMS) to formic acid, molecular chlorine, and nitryl chloride under a variety of flow and pressure conditions. The sensitivity of the Q-CIMS, with the VUV-IS, reached up to ∼700 Hz pptv−1, with detection limits of less than 1 pptv for a 1 min integration period. The reliability of the Q-CIMS with a VUV-IS is demonstrated with data from a month-long ground-based field campaign. The VUV-IS is further tested by operation on a high-resolution time-of-flight CIMS (TOF-CIMS). Sensitivities greater than 25 Hz pptv−1 were obtained for formic acid and molecular chlorine, which were similar to that obtained with a radioactive source. In addition, the mass spectra from sampling ambient air was cleaner with the VUV-IS on the TOF-CIMS compared to measurements using a radioactive source. These results demonstrate that the VUV lamp is a viable substitute for radioactive ion sources on I−-CIMS systems for most applications. In addition, initial tests demonstrate that the VUV-IS can be extended to other reagent ions by the use of VUV absorbers with low IPs to serve as a source of photoelectrons for high IP electron attachers, such as SF6-.

scholarly journals A switchable reagent ion high resolution time-of-flight chemical ionization mass spectrometer for real-time measurement of gas phase oxidized species: characterization from the 2013 southern oxidant and aerosol study

2015 ◽  
Vol 8 (7) ◽  
pp. 2945-2959 ◽  
Author(s):  
P. Brophy ◽  
D. K. Farmer
Keyword(s):  
High Resolution ◽  
Formic Acid ◽  
Gas Phase ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Time Of Flight ◽  
Ionization Mass ◽  
Resolution Time ◽  
Limit Of Quantification ◽  
Reduced Pressure

Abstract. A novel configuration of the Aerodyne high resolution time-of-flight chemical ionization mass spectrometer (HR-TOF-CIMS) as a switchable reagent ion (SRI) HR-TOF-CIMS is presented and described along with data collected at the Southern Oxidant and Aerosol Study (SOAS) during the summer of 2013. The calibration system and reduced pressure gas phase inlet are characterized. The average limit of detection and limit of quantification for formic acid during SOAS are 82 and 863 ppt, respectively, corresponding to an average sensitivity of 13 ± 5 Hz ppt−1. Hourly background determinations and calibrations are shown to be essential for tracking instrument performance and accurately quantifying formic acid. Maximum daytime formic acid concentrations of 10 ppb are reported during SOAS, and a strong diel cycle is observed leading to nighttime concentrations below the limit of quantification. Other species presented exhibit diel behavior similar to formic acid. The concept of the mass defect enhancement plot and the use of signal-to-noise are described in detail as a method for investigating HR-TOF-CIMS spectra in an effort to reduce data complexity.

scholarly journals Measurements of hydroperoxy radicals (HO<sub>2</sub>) at atmospheric concentrations using bromide chemical ionization mass spectrometry

2018 ◽  
Author(s):  
Sascha R. Albrecht ◽  
Anna Novelli ◽  
Andreas Hofzumahaus ◽  
Sungah Kang ◽  
Yare Baker ◽  
...  
Keyword(s):  
Water Vapor ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Limit Of Detection ◽  
Ion Source ◽  
Detection Sensitivity ◽  
Detection Methods ◽  
Ionization Mass ◽  
Key Species ◽  
Atmospheric Concentrations

Abstract. Hydroxyl and hydroperoxy radicals are key species for the understanding of atmospheric oxidation processes. Their measurement is challenging due to their high reactivity, therefore very sensitive detection methods are needed. Within this study, the measurement of hydroperoxy radicals (HO2) using chemical ionization combined with an high resolution time of flight mass spectrometer (Aerodyne Research Inc.) employing bromide as primary ion is presented. The 1σ limit of detection of 4.5 × 107 molecules cm−3 for a 60 s measurement is below typical HO2 concentrations found in the atmosphere. The detection sensitivity of the instrument is affected by the presence of water vapor. Therefore, a water vapor dependent calibration factor that decreases approximately by a factor of 2 if the water vapor mixing ratio increases from 0.1 to 1.0 % needs to be applied. An instrumental background most likely generated by the ion source that is equivalent to a HO2 concentration of 1.5 ± 0.2 × 108 molecules cm−3 is subtracted to derive atmospheric HO2 concentrations. This background can be determined by overflowing the inlet with zero air. Several experiments were performed in the atmospheric simulation chamber SAPHIR at the Forschungszentrum Jülich to test the instrument performance by comparison to the well-established laser-induced fluorescence (LIF) technique for measurements of HO2. A high linear correlation coefficient of R2 = 0.87 is achieved. The slope of the linear regression of 1.07 demonstrates the good absolute agreement of both measurements. Chemical conditions during 15 experiments allowed testing the instrument’s behavior in the presence of atmospheric concentrations of H2O, NOx and O3. No significant interferences from these species were observed. All these facts are demonstrating a reliable measurement of HO2 by the chemical ionization mass spectrometer presented.

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