Preprints
https://doi.org/10.5194/amt-2023-123
https://doi.org/10.5194/amt-2023-123
15 Jun 2023
 | 15 Jun 2023
Status: a revised version of this preprint was accepted for the journal AMT and is expected to appear here in due course.

Comparison of temperature dependent calibration methods of an instrument to measure OH and HO2 radicals using laser-induced fluorescence spectroscopy

Frank A. F. Winiberg, William J. Warman, Charlotte A. Brumby, Graham Boustead, Iustinian G. Bejan, Thomas H. Speak, Dwayne E. Heard, Daniel Stone, and Paul W. Seakins

Abstract. Laser Induced Fluorescence (LIF) spectroscopy has been widely applied to fieldwork measurements of OH radicals, and of HO2, following conversion to OH, over a wide variety of conditions, on different platforms, and in simulation chambers. Conventional calibration of HOx (OH + HO2) instruments has mainly relied on a single method, generating known concentrations of HOx from H2O vapour photolysis in a flow of zero air impinging just outside the sample inlet (SHOx = CHOx.[HOx], where SHOx is the observed signal and CHOx is the calibration factor). The FAGE (Fluorescence Assay by Gaseous Expansion) apparatus designed for HOx measurements in the Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC) at the University of Leeds has been used to examine the sensitivity of FAGE to external gas temperatures (266 – 348 K).

The conventional calibration methods give the temperature dependence of COH (relative to the value at 293 K) of (0.0059 ± 0.0015) K-1 and CHO2 of (0.014 ± 0.013) K-1. Errors are 2σ. COH was also determined by observing the decay of hydrocarbons (typically cyclohexane) caused by OH reactions giving COH (again, relative to the value at 293 K) of (0.0038 ± 0.0007) K-1. Additionally, CHO2 was determined based on the second order kinetics of HO2 recombination with the temperature dependence of CHO2, relative to 293 K being (0.0064 ± 0.0034) K-1.

The temperature dependence of CHOx depends on HOx number density, quenching, relative population of the probed OH rotational level and HOx transmission from inlet to detection axis. The first three terms can be calculated and, in combination with the measured values of CHOx, show that HOx transmission increases with temperature. Comparisons with other instruments and the implications of this work are discussed.

Frank A. F. Winiberg et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2023-123', Anonymous Referee #1, 09 Jul 2023
    • AC1: 'Reply on RC1', Paul Seakins, 18 Aug 2023
  • RC2: 'Comment on amt-2023-123', Anonymous Referee #2, 20 Jul 2023
    • AC2: 'Reply on RC2', Paul Seakins, 18 Aug 2023

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2023-123', Anonymous Referee #1, 09 Jul 2023
    • AC1: 'Reply on RC1', Paul Seakins, 18 Aug 2023
  • RC2: 'Comment on amt-2023-123', Anonymous Referee #2, 20 Jul 2023
    • AC2: 'Reply on RC2', Paul Seakins, 18 Aug 2023

Frank A. F. Winiberg et al.

Frank A. F. Winiberg et al.

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Short summary
OH and HO2 are key reactive intermediates in the Earth's atmosphere. Accurate measurements in either the field or in simulation chambers provide a good test for chemical mechanisms. Fluorescence techniques have the appropriate sensitivity for detection but require calibration. This paper compares different methods of calibration and specifically how calibration factors vary across a temperature range relevant to atmospheric and chamber determinations.