Solubility of nitrous acid (HONO) in ammonium sulfate solutions

Abstract

The Henry's law solubility of nitrous acid (HONO) has been studied in ammonium sulfate solutions as a function of salt concentration in the range 5–39.2 wt.% and temperature between 263 and 298 K by measuring the distribution of HONO between the gas and liquid phases using a bubbler-type gas–liquid reactor. Gas phase concentrations have been measured by tuneable diode laser spectrometry, whereas the liquid phase has been analysed by ion chromatography.

An exponential dependence of the Henry's law constant (K_H) on c_(NH4)2SO4 has been observed with increasing ammonium sulfate concentration caused by the salt effect which is described by the Setschenow equation. The values of ΔH_sol and ΔS_sol for the dissolution of HONO have been determined as a function of ammonium sulfate concentration from the temperature dependence of K_H. The results were fitted to a two-parameter equation that allows the calculation of the solubility of HONO in the temperature and concentration ranges studied. The Henry's law constant of HONO in ammonium sulfate solutions is well described by: K_H = A_(T) exp(B_(T)c_(NH4)2SO4) mol kg⁻¹ bar⁻¹ with A_(T) = 3.06 × 10⁻⁶ exp(4932T⁻¹) mol kg⁻¹ bar⁻¹B_(T) = 17.6T⁻¹ − 0.083 wt.%⁻¹ and c_(NH4)2SO4 in wt.% and T in K. From the calculated values it can be concluded, that for a tropospheric ammonium sulfate aerosol scenario most HONO will be found in the gas phase.