SOLUBILITY OF NITROUS-ACID (HONO) IN AMMONIUM-SULFATE SOLUTIONS

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 t he distribution of HONO between the gas and liquid phases using a bubb ler-type gas-liquid reactor. Gas phase concentrations have been measur ed 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 incr easing ammonium sulfate concentration caused by the salt effect which is described by the Setschenow equation. The values of Delta H-sol and Delta S-sol for the dissolution of HONO have been determined as a fun ction of ammonium sulfate concentration from the temperature dependenc e of K-H. The results were fitted to a two-parameter equation that all ows the calculation of the solubility of HONO in the temperature and c oncentration ranges studied. The Henry's law constant of HONO in ammon ium sulfate solutions is well described by: K-H = A((T)) exp(B-(T)C((N H4)2SO4)) mol kg(-1) bar(-1) with A((T)) = 3.06 x 10(-6) exp(4932T(-1) ) mol kg(-1) bar(-1) B-(T) = 17.6T(-1) - 0.083 wt.%(-1) and c((NH4)2SO 4) in wt.% and T in K. From the calculated values it can be concluded, that for a tropospheric ammonium sulfate aerosol scenario most HONO w ill be found in the gas phase.