Preprints
https://doi.org/10.5194/amt-2021-332
https://doi.org/10.5194/amt-2021-332

  03 Nov 2021

03 Nov 2021

Review status: this preprint is currently under review for the journal AMT.

A Source for the Continuous Generation of Pure and Quantifiable HONO Mixtures

Guillermo Villena and Jörg Kleffmann Guillermo Villena and Jörg Kleffmann
  • Department of Physical and Theoretical Chemistry, Faculty for Mathematics and Natural Sciences, University of Wuppertal, 42097 Wuppertal, Germany

Abstract. A continuous source for the generation of pure HONO mixtures was developed and characterized, which is based on the Henry’s law solubility of HONO in acidic aqueous solutions. With the help of a peristaltic pump diluted nitrite and sulfuric acid solutions are mixed in a temperature-controlled stripping coil, which is operated with pure nitrogen or synthetic air at gas flow rates of 0.5–2 L min-1. Caused by the acidic conditions of the aqueous phase (pH ≈ 2.5), nitrite is almost completely converted into HONO, which partitions to the gas phase limited by its known solubility in water. The source shows a fast time response of ~2 min (0–90 %) at higher concentrations and an excellent long-time stability (2&sigma; noise <1 %). The HONO emission of the source perfectly correlates with the nitrite concentration from the sub-ppb range up to 500 ppb. The rate of NOx formation increases quadratically with the HONO concentration from non-detectable values at atmospheric relevant HONO concentrations reaching a NOx content of 1.6 % at 500 ppb. A general equation based on Henry’s law is developed, whereby the HONO concentration of the source can be calculated using measured experimental parameters, i.e. nitrite concentration, liquid flow rates, gas flow rate, pH of the solution and temperature of the stripping coil. In the equation, the known Henry’s law constant of HONO in sulfuric acid solutions is used. For the calculation of the effective Henry’s law constant, the acid dissociation equilibrium of HONO/nitrite is used as a variable to adjust the theoretical HONO concentration to the measured values. From the average of all experimental data the equilibrium of HONO/nitrite is well described by pKa = 1021.53/T – 0.449. The pKa of 3.0±0.1 (1&sigma;) at 25 °C is in good agreement with the range of 2.8–3.28 published in former studies. A standard deviation between all measured and theoretical HONO concentrations of only ±3.8 % was observed and a conservative upper limit accuracy of the HONO concentration of better 10 % is estimated. Thus, for the first time, a stable HONO source is developed, which can be used for the absolute calibration of HONO instruments.

Guillermo Villena and Jörg Kleffmann

Status: open (until 08 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-332', Anonymous Referee #2, 22 Nov 2021 reply
    • AC1: 'Reply on RC1', Jörg Kleffmann, 23 Nov 2021 reply
  • RC2: 'Comment on amt-2021-332', Anonymous Referee #1, 22 Nov 2021 reply
    • AC2: 'Reply on RC2', Jörg Kleffmann, 23 Nov 2021 reply

Guillermo Villena and Jörg Kleffmann

Guillermo Villena and Jörg Kleffmann

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Short summary
A continuous source for the generation of pure HONO mixtures was developed and characterized, which is based on the Henry’s law solubility of HONO in acidic aqueous solutions. The source shows a fast time response, an excellent long-time stability and can be easily adjusted to HONO mixing ratios in the range 0.1–500 ppb. A general equation based on Henry’s law is developed, whereby the HONO concentration of the source can be absolutely calculated with an accuracy of better 10 %.