A Unique Method for Laboratory Quantification of Gaseous Nitrous Acid (HONO) Using the Reaction HONO + HCl → ClNO + H₂O

Abstract

Although the formation and reactions of gaseous nitrous acid (HONO) in the atmosphere are of great interest, it is difficult to accurately measure HONO both in the atmosphere and in laboratory systems. We report a new technique for quantifying gaseous HONO in laboratory systems. The method utilizes the reaction of gas phase HONO with an excess of HCl gas to produce nitrosyl chloride (ClNO), which is readily quantified using FTIR. HONO was formed by flowing N2 over the surface of an aqueous HCl solution and through a bed of NaNO2, then directly into a 561 L chamber. An excess of gaseous HCl was added to the chamber to initiate the reaction in N2 at room temperature and 1 atm total pressure. The loss of HONO was followed by DOAS and FTIR and the formation of ClNO was measured by FTIR. While direct measurement of HONO by FTIR is limited by uncertainties in the available infrared absorption cross sections, calibration for ClNO is readily carried out since ClNO can be synthesized with high purity. The stoichiometry for ClNO formed to HONO reacted was determined to be 0.9 ± 0.2 (1σ). The concentration−time profiles for both HONO and ClNO were fitted with a kinetics model which gave a rate constant for the reaction HONO + HCl ClNO + H2O of k 1 ≤ (1.9 ± 1.3) × 10-19 cm3 molecule-1 s-1 (2σ) at 297 K. This should be taken as the upper limit for the gas phase reaction since some contribution from heterogeneous reaction at the chamber walls cannot be conclusively ruled out.

Chlorine activation indoors and outdoors via surface-mediated reactions of nitrogen oxides with hydrogen chloride

“…The product was Ϸ95% pure (determined by FTIR, 10 cm path length) with the main impurities being HNO3 and NO2. Nitrous acid was generated by the method of Wingen et al (31). Silica pellets were formed by hand pressing SiO2 powder (Cab-O-Sil, Cabot) in a precleaned stainless steel press.…”

“…Because HONO is known to react with HCl heterogeneously to form ClNO (30,31), the possibility that HONO is initially formed in reaction [3] and then reacts further with HCl to form ClNO must be considered. This can be ruled out because the amount of ClNO that is possible from the direct reaction of HCl with gaseous HONO at 80 min (Fig.…”

The effects of nitrate on the heterogeneous uptake of sulfur dioxide on hematite

“…5, there are no absorption peaks of gas-phase HONO before 430 min, but several weak HONO absorption peaks centered at 1262, 850, and 790 cm −1 are observed when the reaction time is prolonged to 1170 min (Fig. 5d) (Wingen et al, 2000). The difference spectrum shown in Fig.…”

A compact, high-purity source of HONO validated by Fourier Transform Infrared and Thermal Dissociation Cavity Ring-down Spectroscopy

“…Nitrosyl chloride can be produced by reaction of HONO with gas-phase or wall-adsorbed HCl (Zhang et al, 1996;Wingen et al, 2000) or by reaction of two equivalents of NO2 with particulate phase Cl - (Weis and Ewing, 1999), though the relatively low mixing ratios of NO2 in this system makes this reaction less 155 likely.…”