Preprints
https://doi.org/10.5194/egusphere-2025-4183
https://doi.org/10.5194/egusphere-2025-4183
29 Sep 2025
 | 29 Sep 2025
Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).

High-purity nitrous acid (HONO) generation and quantification using broadband cavity-enhanced absorption spectroscopy (BBCEAS)

Alexis P. Harper, Callum E. Flowerday, Zachary Giauque, Kaitlyn Brewster, Ryan Thalman, and Jaron C. Hansen

Abstract. Nitrous acid (HONO) is a key atmospheric precursor to hydroxyl radicals (OH), which drive oxidation processes in the troposphere. Accurate quantification of HONO is essential for modelling atmospheric chemistry but is often challenging due to low ambient concentrations, significant wall losses from instruments with inlets, and interference from co-produced nitrogen dioxide (NO2). Laboratory generation methods frequently struggle to produce HONO in both high purity and usable quantities. This study introduces a simple, scalable method for generating high-purity HONO via the reaction of hydrochloric acid (HCl) and sodium nitrite (NaNO2) in a multi-bubbler system. The method incorporates a thermal "catch and release" mechanism to selectively trap HONO and separate it from NO2 prior to analysis. While the melting point of NO2 is well-established at -9 °C, the melting point of HONO was monitored and determined to be -4 °C, enabling the thermal separation mechanism to function effectively. Broadband cavity-enhanced absorption spectroscopy (BBCEAS) was used for detection and quantification in the 329–344 nm region. Systematic optimization of bubbler temperatures, carrier gas flow rates, capture durations, and moisture levels yielded HONO purities greater than 96 %. This method enables reliable and flexible production of high-purity HONO, making it well-suited for use in laboratory-based chamber studies and instrument calibration applications.

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Alexis P. Harper, Callum E. Flowerday, Zachary Giauque, Kaitlyn Brewster, Ryan Thalman, and Jaron C. Hansen

Status: open (until 03 Nov 2025)

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Alexis P. Harper, Callum E. Flowerday, Zachary Giauque, Kaitlyn Brewster, Ryan Thalman, and Jaron C. Hansen
Alexis P. Harper, Callum E. Flowerday, Zachary Giauque, Kaitlyn Brewster, Ryan Thalman, and Jaron C. Hansen

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Short summary
In this study, we developed a new way to produce and measure nitrous acid, an important atmospheric gas that can be difficult to synthesize. By carefully controlling temperatures and reaction conditions, we created high-purity (<96 %) samples and showed how they can be stored and released when needed. This advance makes it easier to study how nitrous acid contributes to air pollution and atmospheric interactions, while also improving tools for laboratory experiments and instrument testing.
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