The heterogeneous reaction of NO2 with NH4Cl: A molecular diffusion tube study
Journal of Atmospheric Chemistry, 50 (2):
171--194 (January 2005)DOI: 10.1007/s10874-005-5898-4
Abstract
The heterogeneous interaction of nitrogen dioxide with ammonium chloride was investigated in a molecular diffusion tube experiment at 295-335 K and interpreted using Monte Carlo trajectory calculations. The surface residence time (tau(surf)) of NO2 on NH4Cl is equal to 15 mu s at 295 K, increases with temperature up to 323 K (tau(surf)=45 mu s) and probably decreases beyond 323 K. The same experiment also yields uptake coefficients, gamma, which are derived from the absolute number of surviving molecules effusing out of the diffusion tube. The rate of uptake of NO2 on NH4Cl followed a rate law first order in NO2 and the uptake coefficient gamma is equal to 7x10(-5) at 295 K, increases with temperature up to 323 K (gamma=2.1x10(-4)) and probably decreases beyond 323 K. Nitrous acid, water and nitrogen were detected as products. From these products, it is concluded that the reaction of NO2 with NH4Cl is a reverse disproportionation reaction where two moles of NO2 result in ammonium nitrite, NH4NO2, as an intermediate, and nitryl chloride, NO2Cl. NH4NO2 decomposes in two pathways, one to nitrous acid, HONO and NH3, the other to nitrogen and water. The branching ratio for the production of HONO+NH3 to that of N-2+H2O is approximately 20 at 298 K and increases with increasing temperature.