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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/amt-2018-99
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
05 Apr 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).
A novel semi-direct method to measure OH reactivity by chemical ionisation mass spectrometry (CIMS)
Jennifer B. A. Muller, Thomas Elste, Christian Plass-Dülmer, Georg Stange, Robert Holla, Anja Claude, Jennifer Englert, Stefan Gilge, and Dagmar Kubistin Meteorologisches Observatorium Hohenpeissenberg , Deutscher Wetterdienst (DWD), 82383 Hohenpeissenberg, Germany
Abstract. An operational chemical ionisation mass spectrometer (CIMS) for hydroxyl radical (OH) and sulfuric acid (H2SO4) concentration measurements was adapted to include observations of OH reactivity, which is the inverse of OH lifetime, for long-term monitoring at the Global Atmosphere Watch (GAW) site Hohenpeissenberg (MOHp), Germany. OH measurement using CIMS is achieved by reacting OH with SO2, leading to the production of H2SO4 which is then detected. The adaptation for OH reactivity consists of the implementation of a second SO2 injection, at a fixed point further down flow in the sample tube to detect the OH decay caused by reactions with OH reactants present in the sample.

The method can measure OH reactivity between below 1 and 40 s−1 with the upper limit due to the fixed positioning of the second SO2 injection. To determine OH reactivity from OH concentration measurements, the reaction time between the two titration zones and OH wall losses in the sample tube need to be determined accurately through OH reactivity calibration. Potential measurement artefacts as a result of HOx recycling in the presence of NO have to be considered. Therefore NO contamination from gases used in instrument operation must be minimised and ambient NO must be measured concurrently to determine the measurement error.

This CIMS system is shown here to perform very well for OH reactivity below 15 s−1 and NO concentrations below 4 ppb, both values that are rarely exceeded at the MOHp site. Thus when deployed in suitable chemical environments, this method can provide valuable continuous long-term measurements of OH reactivity. The characterisation utilises results from chamber, laboratory and modelling studies and includes the discussion and quantification of sources of uncertainties.

Citation: Muller, J. B. A., Elste, T., Plass-Dülmer, C., Stange, G., Holla, R., Claude, A., Englert, J., Gilge, S., and Kubistin, D.: A novel semi-direct method to measure OH reactivity by chemical ionisation mass spectrometry (CIMS), Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2018-99, in review, 2018.
Jennifer B. A. Muller et al.
Jennifer B. A. Muller et al.
Jennifer B. A. Muller et al.

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Short summary
The hydroxyl radical (OH) largely controls tropospheric trace gas removal and the inverse of OH lifetime, OH reactivity, is a useful measure to investigate the oxidation capacity of the atmosphere. This paper presents a novel method to measure OH reactivity using an operational chemical ionisation mass spectrometer (CIMS) for OH measurements at the GAW site Hohenpeissenberg, Germany. It includes the analysis of measurement uncertainties and demonstrates its suitability for long-term monitoring.
The hydroxyl radical (OH) largely controls tropospheric trace gas removal and the inverse of OH...
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