scholarly journals A low-activity ion source for measurement of atmospheric gases by chemical ionization mass spectrometry

2020 ◽  
Vol 13 (5) ◽  
pp. 2473-2480 ◽  
Author(s):  
Young Ro Lee ◽  
Yi Ji ◽  
David J. Tanner ◽  
L. Gregory Huey

Abstract. Most I−-CIMSs (iodide chemical ionization mass spectrometers) for measurement of atmospheric trace gases utilize a radioactive ion source with an initial activity of 10 or 20 mCi of 210Po. In this work, we characterize a 210Po ion source with an initial activity of 1.5 mCi that can be easily constructed from commercially available components. The low level of radioactive activity of this source significantly reduces regulatory burden with storage and shipping relative to higher-activity sources. We compare the sensitivity of the low-activity source (LAS) to a standard 20 mCi source, as a function of carrier gas flow and flow tube pressure, for peroxyacetyl nitrate (PAN), formic acid (HCO2H), molecular chlorine (Cl2) and nitryl chloride (ClNO2), using an I−-CIMS. The LAS provides 2 to 5 times less sensitivity than that of the standard source even though the ratio of activity is approximately 13. However, detection limits of less than 2 pptv for the tested compounds are achieved for integration times on the order of a minute. The sensitivity of the LAS is less dependent on the magnitude of the carrier gas than a standard source. In addition, the LAS provides maximum sensitivity at relatively low carrier gas flows. Finally, we demonstrate that the LAS can be used to measure PAN in the remote atmosphere from an aircraft by showing data obtained on the NASA DC-8 during the Atmospheric Tomography (ATom) mission. In summary, the LAS may be an excellent substitute for a standard ion source in short-term field deployments.

2019 ◽  
Author(s):  
Young Ro Lee ◽  
Yi Ji ◽  
David J. Tanner ◽  
L. Gregory Huey

Abstract. Most I--CIMS (iodide-chemical ionization mass spectrometers) for measurement of atmospheric trace gases utilize a radioactive ion source with an initial activity of 10 or 20 mCi of 210Po. In this work, we characterize a 210Po ion source with an initial activity of 1.5 mCi that can be easily constructed from commercially available components. The low level of radioactive activity of this source significantly reduces complications with storage and shipping relative to higher activity sources. We compare the sensitivity of the low activity source (LAS) to a standard 20 mCi source, as a function of carrier gas flow and flow tube pressure, for peroxyacetyl nitrate (PAN), formic acid (HCO2H) molecular chlorine (Cl2), and nitryl chloride (ClNO2) using an I--CIMS. The LAS provides 2 to 5 times less sensitivity than that of the standard source even though the ratio of activity is approximately 13. However, detection limits of less than 2 pptv for the tested compounds are achieved for integration times of the order of a minute. The sensitivity of the LAS is less dependent on the magnitude of the carrier gas than a standard source. In addition, the LAS provides maximum sensitivity at relatively low carrier gas flows. Finally, we demonstrate that the LAS can be used to measure PAN in the remote atmosphere from an aircraft by showing data obtained on the NASA DC-8 during the Atmospheric Tomography (ATom) mission. In summary, the LAS may be an excellent substitute for a standard ion source in some field applications.


2011 ◽  
Vol 11 (10) ◽  
pp. 4755-4766 ◽  
Author(s):  
D. R. Benson ◽  
J. H. Yu ◽  
A. Markovich ◽  
S.-H. Lee

Abstract. Ternary homogeneous nucleation (THN) of H2SO4, NH3 and H2O has been used to explain new particle formation in various atmospheric regions, yet laboratory measurements of THN have failed to reproduce atmospheric observations. Here, we report first laboratory observations of THN made under conditions relevant to the lower troposphere ([H2SO4] of 106–107 cm−3, [NH3] of 0.08–20 ppbv, and a temperature of 288 K). Our observations show that NH3 can enhance atmospheric H2SO4 aerosol nucleation and the enhancement factor (EF) in nucleation rate (J) due to NH3 (the ratio of J measured with vs. without NH3) increases linearly with increasing [NH3] and increases with decreasing [H2SO4] and RH. Two chemical ionization mass spectrometers (CIMS) are used to measure [H2SO4] and [NH3], as well as possible impurities of amines in the nucleation system. Aerosol number concentrations are measured with a water condensation counter (CPC, TSI 3786). The slopes of Log J vs. Log [H2SO4], Log J vs. Log RH, and Log J vs. Log [NH3] are 3–5, 1–4, and 1, respectively. These slopes and the threshold of [H2SO4] required for the unity nucleation vary only fractionally in the presence and absence of NH3. These observations can be used to improve aerosol nucleation models to assess how man-made SO2 and NH3 affect aerosol formation and CCN production at the global scale.


2020 ◽  
Author(s):  
Mingyi Wang ◽  
Xu-Cheng He ◽  
Henning Finkenzeller ◽  
Siddharth Iyer ◽  
Dexian Chen ◽  
...  

Abstract. Iodine species are important in the marine atmosphere for oxidation and new-particle formation. Understanding iodine chemistry and iodine new-particle formation requires high time resolution, high sensitivity, and simultaneous measurements of many iodine species. Here, we describe the application of bromide chemical ionization mass spectrometers (Br-CIMS) to this task. During iodine new-particle formation experiments in the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber, we have measured gas-phase iodine species and sulfuric acid using two Br-CIMS, one coupled to a Multi-scheme chemical IONization inlet (Br-MION-CIMS) and the other to a Filter Inlet for Gasses and AEROsols inlet (Br-FIGAERO-CIMS). From offline calibrations and inter-comparisons with other instruments attached to the CLOUD chamber, we have quantified the sensitivities of the Br-MION-CIMS to HOI, I2, and H2SO4 and obtain detection limits of 5.8 × 106, 6.3 × 105, and 2.0 × 105 molec cm−3, respectively, for a 2-min integration time. From binding energy calculations, we estimate the detection limit for HIO3 to be 1.2 × 105 molec cm−3, based on an assumption of maximum sensitivity. Detection limits in the Br-FIGAERO-CIMS are around one order of magnitude higher than those in the Br-MION-CIMS; for example, the detection limits for HOI and HIO3 are 3.3 × 107 and 5.1 × 106 molec cm−3, respectively. Our comparisons of the performance of the MION inlet and the FIGAERO inlet show that bromide chemical ionization mass spectrometers using either atmospheric pressure or reduced pressure interfaces are well-matched to measuring iodine species and sulfuric acid in marine environments.


2015 ◽  
Vol 8 (12) ◽  
pp. 13567-13607 ◽  
Author(s):  
T. Jurkat ◽  
S. Kaufmann ◽  
C. Voigt ◽  
D. Schäuble ◽  
P. Jeßberger ◽  
...  

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.


2019 ◽  
Author(s):  
Alan Wei ◽  
Anuj Joshi ◽  
Yuxuan Chen ◽  
J Scott McIndoe

<p>All instruments with detectors are prone to saturation effects at high concentration, and mass spectrometers are no exception. The very high sensitivity of mass spectrometry makes the onset of saturation occur at lower concentrations than other methods, and in cases where the analyte of interest is very reactive, concentrations at which saturation can be problematic may be necessary in order to ensure decomposition is mitigated. Indications that saturation is occurring are provided, and some data processing strategies are outlined, followed by a range of detuning strategies that may be employed to reduce saturation effects in the context of electrospray ionization mass spectrometry (ESI-MS), including lowering voltages on detector or capillary, increasing cone gas flow rates, or adjusting the probe position. A combination of strategies generally allows researchers to make the best possible compromises when studying compounds at relatively high concentration.</p>


2021 ◽  
Vol 14 (6) ◽  
pp. 4187-4202
Author(s):  
Mingyi Wang ◽  
Xu-Cheng He ◽  
Henning Finkenzeller ◽  
Siddharth Iyer ◽  
Dexian Chen ◽  
...  

Abstract. Iodine species are important in the marine atmosphere for oxidation and new-particle formation. Understanding iodine chemistry and iodine new-particle formation requires high time resolution, high sensitivity, and simultaneous measurements of many iodine species. Here, we describe the application of a bromide chemical ionization mass spectrometer (Br-CIMS) to this task. During the iodine oxidation experiments in the Cosmics Leaving OUtdoor Droplets (CLOUD) chamber, we have measured gas-phase iodine species and sulfuric acid using two Br-CIMS, one coupled to a Multi-scheme chemical IONization inlet (Br-MION-CIMS) and the other to a Filter Inlet for Gasses and AEROsols inlet (Br-FIGAERO-CIMS). From offline calibrations and intercomparisons with other instruments, we have quantified the sensitivities of the Br-MION-CIMS to HOI, I2, and H2SO4 and obtained detection limits of 5.8 × 106, 3.8 × 105, and 2.0 × 105 molec. cm−3, respectively, for a 2 min integration time. From binding energy calculations, we estimate the detection limit for HIO3 to be 1.2 × 105 molec. cm−3, based on an assumption of maximum sensitivity. Detection limits in the Br-FIGAERO-CIMS are around 1 order of magnitude higher than those in the Br-MION-CIMS; for example, the detection limits for HOI and HIO3 are 3.3 × 107 and 5.1 × 106 molec. cm−3, respectively. Our comparisons of the performance of the MION inlet and the FIGAERO inlet show that bromide chemical ionization mass spectrometers using either atmospheric pressure or reduced pressure interfaces are well-matched to measuring iodine species and sulfuric acid in marine environments.


2019 ◽  
Author(s):  
Alan Wei ◽  
Anuj Joshi ◽  
Yuxuan Chen ◽  
J Scott McIndoe

<p>All instruments with detectors are prone to saturation effects at high concentration, and mass spectrometers are no exception. The very high sensitivity of mass spectrometry makes the onset of saturation occur at lower concentrations than other methods, and in cases where the analyte of interest is very reactive, concentrations at which saturation can be problematic may be necessary in order to ensure decomposition is mitigated. Indications that saturation is occurring are provided, and some data processing strategies are outlined, followed by a range of detuning strategies that may be employed to reduce saturation effects in the context of electrospray ionization mass spectrometry (ESI-MS), including lowering voltages on detector or capillary, increasing cone gas flow rates, or adjusting the probe position. A combination of strategies generally allows researchers to make the best possible compromises when studying compounds at relatively high concentration.</p>


2020 ◽  
Author(s):  
Yi Ji ◽  
L. Gregory Huey ◽  
David J. Tanner ◽  
Young Ro Lee ◽  
Patrick R. Veres ◽  
...  

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.


2016 ◽  
Vol 9 (4) ◽  
pp. 1907-1923 ◽  
Author(s):  
Tina Jurkat ◽  
Stefan Kaufmann ◽  
Christiane Voigt ◽  
Dominik Schäuble ◽  
Philipp Jeßberger ◽  
...  

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.


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