Abstract. We report on the development, characterization, and fielddeployment of a fast-time-response sensor for measuring ozone (O3) andnitrogen dioxide (NO2) concentrations utilizing chemical ionizationtime-of-flight mass spectrometry (CI-ToFMS) with oxygen anion(O2-) reagent ion chemistry. Wedemonstrate that the oxygen anion chemical ionization mass spectrometer(Ox-CIMS) is highly sensitive to both O3 (180 counts s−1 pptv−1) and NO2 (97 counts s−1 pptv−1), corresponding todetection limits (3σ, 1 s averages) of 13 and 9.9 pptv,respectively. In both cases, the detection threshold is limited by themagnitude and variability in the background determination. The short-termprecision (1 s averages) is better than 0.3 % at 10 ppbv O3 and 4 %at 10 pptv NO2. We demonstrate that the sensitivity of the O3measurement to fluctuations in ambient water vapor and carbon dioxide isnegligible for typical conditions encountered in the troposphere. Theapplication of the Ox-CIMS to the measurement of O3 vertical fluxesover the coastal ocean, via eddy covariance (EC), was tested during the summer of2018 at Scripps Pier, La Jolla, CA. The observed mean ozone depositionvelocity (vd(O3)) was 0.013 cm s−1 with a campaign ensemblelimit of detection (LOD) of 0.0027 cm s−1 at the 95 % confidencelevel, from each 27 min sampling period LOD. The campaign mean and 1standard deviation range of O3 mixing ratios was 41.2±10.1 ppbv. Several fast ozone titration events from local NO emissions weresampled where unit conversion of O3 to NO2 was observed,highlighting instrument utility as a total odd-oxygen (Ox=O3+NO2) sensor. The demonstrated precision, sensitivity, and timeresolution of this instrument highlight its potential for directmeasurements of O3 ocean–atmosphere and biosphere–atmosphere exchangefrom both stationary and mobile sampling platforms.
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A vacuum ultraviolet ion source (VUV-IS) for iodide–chemical ionization mass spectrometry: a substitute for radioactive ion sources
Abstract. A new ion source (IS) utilizing vacuum ultraviolet (VUV) light is developed and characterized for use with iodide–chemical ionization massspectrometers (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 formI−, which serves as the reagent ion for the CIMS. The VUV-IS is characterized by measuring the sensitivity of a quadrupole CIMS (Q-CIMS) toformic acid, molecular chlorine, and nitryl chloride under a variety of flow and pressure conditions. The sensitivity of the Q-CIMS, with theVUV-IS, reached up to ∼700 Hz pptv−1, with detection limits of less than 1 pptv for a 1 min integration period. Thereliability 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 byoperation on a high-resolution time-of-flight CIMS (TOF-CIMS). Sensitivities greater than 25 Hz pptv−1 were obtained for formic acid andmolecular chlorine, which were similar to that obtained with a radioactive source. In addition, the mass spectra from sampling ambient air wascleaner with the VUV-IS on the TOF-CIMS compared to measurements using a radioactive source. These results demonstrate that the VUV lamp is a viablesubstitute for radioactive ion sources on I−-CIMS systems for most applications. In addition, initial tests demonstrate that the VUV-IS canbe 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-.
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- PAR ID:
- 10170363
- Date Published:
- Journal Name:
- Atmospheric Measurement Techniques
- Volume:
- 13
- Issue:
- 7
- ISSN:
- 1867-8548
- Page Range / eLocation ID:
- 3683 to 3696
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/amt-13-3683-2020
