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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 26 Nov 2019

Submitted as: research article | 26 Nov 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Calibration of an airborne HOX instrument using the All Pressure Altitude based Calibrator for HOX Experimentation (APACHE)

Daniel Marno1, Cheryl Ernest1,a, Korbinian Hens1,b, Umar Javed1,2, Thomas Klimach1, Monica Martinez1, Markus Rudolf1, Jos Lelieveld1, and Hartwig Harder1 Daniel Marno et al.
  • 1Atmospheric Chemistry Department, Max Planck Institute for Chemistry, 55128, Mainz, Germany
  • 2Forschungszentrum Jülich GmbH, IEK-8, 52425, Jülich, Germany
  • anow at: Department of Neurology, University Medical Center of the Johannes Gutenberg University Mainz, 55131, Mainz, Germany
  • bnow at: Hübner GmbH & Co KG – Division Hübner Photonics, 34123 Kassel, Germany

Abstract. Laser induced fluorescence (LIF) is a widely used technique for both laboratory-based and ambient atmospheric chemistry measurements. However, LIF instruments require calibrations in order to translate instrument response into concentrations of chemical species. Calibration of LIF instruments measuring OH and HO2 (HOX), typically involves the photolysis of water vapor by 184.9 nm light thereby producing quantitative amounts of OH and HO2. For ground-based systems HOX instruments, this method of calibration is done at one pressure (typically ambient pressure) at the instrument inlet. However, airborne HOX instruments can experience varying cell pressures, internal residence times, temperatures, and humidity during flight. Therefore, replication of such variances when calibrating are essential to acquire the appropriate sensitivities. This requirement resulted in the development of the APACHE (All Pressure Altitude-based Calibrator for HOX Experimentation) chamber. It utilizes photolysis of water vapor, but has the additional ability to alter the pressure at the inlet of the HOX instrument thus relating instrument sensitivity to the external pressure ranges experienced during flight (275 to 1000 mbar). Measurements supported by COMSOL multiphysics and its computational fluid dynamics calculations revealed that, for all pressures explored in this study, APACHE is capable of initializing homogenous flow and maintain near uniform flow speeds across the internal cross-section of the chamber. This reduces the uncertainty regarding average exposure times across the mercury (Hg) UV ring lamp. Two different actinometrical approaches characterized the APACHE UV ring lamp flux as 6.3 x 1014 (± 0.9 x 1014) s-1 depending on pressure. Data presented in this study are the first direct calibrations, performed in a controlled environment using APACHE of an airborne HOX system instrument.

Daniel Marno et al.
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Daniel Marno et al.
Daniel Marno et al.
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Short summary
In this study, a calibration device for OH & HO2 instruments is characterized at pressures 275 to 1000 mbar, allowing instrument pressure sensitivity to be quantified to an accuracy of 17 %, (1σ). Computational fluid dynamic simulations supporting the understanding of interactions between generated HOX and the instrument inlet, led to enhanced determination of factors affecting instrument sensitivity.
In this study, a calibration device for OH & HO2 instruments is characterized at pressures 275...