Behavior of Ammonium Chloride and Ammonium Nitrate in the Atmosphere

The particulate and gaseous matter sampling was carried out at Institute for Nature Study, National Science Museum in Tokyo during June 11~22, 1985, and February 4~9, 1986, in order to investigate the behavior of ammonium chloride and ammonium nitrate in the atmosphere. Gaseous HCl and NH₃ were collected by Na₂CO₃ and H₃PO4 impregnated filters in series, after the removal of particulate matter containing ammonium chloride and ammonium nitrate with Teflon filter. The diffusion denuders were used for the collection of gaseous HNO₃. Each component was extracted with distilled water from the collected samples and its amount was determined by ion chromatography. The average concentrations of gaseous NH₃, HCl and HNO₃ over more than 100 measurements were 0.18, 0, 026, and 0. 006 μmol/m₃ in summer period, and 0. 09, 0.008 and 0. 004 μmol/m³ in winter period, respectively. On the other hand, the average concentrations of particulate ammonium, chloride and nitrate were 0.13, 0.04 and 0.07 μmol/m³ in summer period, and 0.015, 0. 09 and 0. 03 μmol/m³ in winter period, respectively. The concentration ratios NH₈/(NH₃+NH⁴⁺), HC1/(HC1⁺C1^-) and HNO₃/(HNO₃⁺NO^3-) were higher in summer period than those in winter period, and a correlation between these ratios and temperature was observed. Furthermore, a strong correlation between the measured concentration products ([NH₃] [HCl] and [NH₃] [HNO₃]) and reciprocal temperature (l/T) was observed. These results could be explained by the following dissociation equilibria, NH₄Cl(s)⇌NH₃(g)+HCl(g) and NH₄NO₃(s)⇌NH₃+HNO₈(g).