Field measurements of dissociation of ammonium nitrate at a Beijing site

The atmospheric nitric acid, ammonia and ammonium nitrate aerosol were determined simultaneously in a Beijing site to test the equilibrium prediction. Rather good agreement between measurements and theory was found at ambient temperature above 9 degree C at relative humidity below 70%. Below 9 degree C the kinetic constraints preventing rapid attainment equilibrium were observed. A procedure for calculation of dependence of NH sub(4)NO sub(3) aerosol dissociation constants on temperature and relative humidity was given. The seasonal variation of concentrations of NH sub(3), total NH sub(4) super(+) and HNO sub(3) was observed. The seasonal variation of concentrations of HNO sub(3) was caused by dissociation of NH sub(4)NO sub(3) aerosol. The concentrations of NH sub(3) were 1 - 2 order higher than those of HNO sub(3). For formation of NH sub(4)NO sub(3) aerosol the HNO sub(3) was the control reagent. Any increase of HNO sub(3) formed from NO sub(x) would react with NH sub(3) to form NH sub(4)NO sub(3) aerosol in Beijing area except for someday in summer time.