16 May 2022
16 May 2022
Status: this preprint is currently under review for the journal AMT.

Comparison of Two Photolytic Calibration Methods for Nitrous Acid

Andrew Lindsay and Ezra Wood Andrew Lindsay and Ezra Wood
  • Department of Chemistry, Drexel University, Philadelphia, PA, USA

Abstract. Nitrous acid (HONO) plays an important role in tropospheric oxidation chemistry as it is a precursor to the hydroxyl radical. Measurements of HONO have been historically difficult due to instrument interferences and difficulties in sampling and calibration. The traditional calibration method involves generation of HONO by reacting hydrogen chloride vapor with sodium nitrite followed by quantification by various methods (e.g., conversion of HONO to nitric oxide (NO) followed by chemiluminescence detection). Alternatively, HONO can be generated photolytically in the gas-phase by reacting NO with OH radicals generated by H2O photolysis. In this work, we describe and compare two photolytic HONO calibration methods that were used to calibrate an iodide adduct chemical ionization mass spectrometer (CIMS). Both methods are based on the water vapor photolysis method commonly used for OH and HO2 calibrations. The first method is an adaptation of the common chemical actinometry HOx calibration method, in which HONO is calculated based on quantified values for [O3], [H2O], [O2], and the absorption cross sections for H2O and O2 at 184.9 nm. In the second, novel method the HONO concentration is simply determined based on the simultaneous measurements of NO2 formed by the reaction of NO with HO2 from the H2O photolysis. This second, novel approach generally has an improved (lower) calibration uncertainty and is simpler to apply. Calibration uncertainties are typically 30 to 36 % (2σ) for the actinometric method and as low as 9 % (2σ) for the NO2 proxy method, limited by the uncertainty of the NO2 measurements.

Andrew Lindsay and Ezra Wood

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2022-157', Anonymous Referee #1, 06 Jun 2022
  • RC2: 'Comment on amt-2022-157', Anonymous Referee #2, 06 Jun 2022
  • RC3: 'Comment on amt-2022-157', Anonymous Referee #3, 09 Jun 2022
  • CC1: 'Comment on amt-2022-157', Jörg Kleffmann, 09 Jun 2022

Andrew Lindsay and Ezra Wood

Andrew Lindsay and Ezra Wood


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Short summary
Nitrous acid (HONO) is an important source of the main atmospheric oxidant – the hydroxyl radical (OH). Advances in nitrous acid measurement techniques and calibration methods therefore improve our understanding of atmospheric oxidation processes. In this manuscript, we present two calibration methods based on photo-dissociating water vapor. These calibration methods are useful alternatives to conventional calibrations that involve a reacting hydrogen chloride vapor with sodium nitrite.