REACTIONS OF NITROGEN-OXIDES WITH NACL AS MODEL OF SEA SALT AEROSOL

NaCl as the main constituent of atmospheric sea salt microparticles was exposed to NO and NO2 with pressures typical for urban conditions in order to investigate the well known conversion of sea salt in NO(x) polluted atmospheres. The analysis of the solid phase was performed using photoelectron spectroscopy, while gaseous products were detected with a mass spectrometer right in front of the NaCl tablet samples. NO2 was found to convert NaCl to no other solid product than nitrate, while NOCl is released into the gas phase. Depending on temperature part of NOCl is dissociated at the surface to give NO and Cl2. In the presence of water hydrolysis partially forms HCl and HNO2. Within 10(4) sec at T = 298K and 1-mu-bar NO2 > 90% of NaCl in the surface region are converted. No significant depth propagation of the reaction could be detected. Initially the reaction rate is inclining probably due to impeding surface contaminants being removed by reaction. After the initial phase the surface reaction rate was found to decline proportional to C(NaCl2 square-root p(NO2).exp(-28 kJmol-1/RT) with C(NaCl) being the fraction of unconverted NaCl in the surface region. NO reacts only in minute amounts forming nitrite. At T = 298K and 1-mu-bar NO only < 3% of surface NaCl is converted to nitrite within 10(4)sec.