The Heterogeneous Reaction of NO₂ with NH₄Cl: A Molecular Diffusion Tube Study

Authors: Takenaka, Norimichi¹; Rossi, Michel²

Source: Journal of Atmospheric Chemistry, Volume 50, Number 2, February 2005 , pp. 171-194(24)

Publisher: Springer

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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

s at 295 K, increases with temperature up to 323 K ( tau

_surf = 45

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 7 × 10^-5 at 295 K, increases with temperature up to 323 K ( gamma

= 2.1 × 10^-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 N₂ + H₂O is approximately 20 at 298 K and increases with increasing temperature.

Keywords: molecular diffusion tube; nitrogen dioxide; ammonium salts; nitrous acid; uptake coefficient; tropospheric aerosols

Document Type: Research article

DOI: http://dx.doi.org/10.1007/s10874-005-5898-4

Affiliations: 1: Laboratory of Environmental Chemistry, Department of Applied Materials Science, Graduate School of Engineering, Osaka Prefecture University, Gakuen-cho 1-1, Sakai, Osaka, 599-8531, Japan, Email: takenaka@ams.osakafu-u.ac.jp 2: Laboratoire de Pollution Atmosphérique et Sol (LPAS), Faculté Environnement Naturel, Construit et Architectural (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland,

Publication date: 2005-02-01