Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 2 3 2002 10.5194/acp-2-235-2002 http://www.atmos-chem-phys.net/2/235/2002/ http://www.atmos-chem-phys.net/2/235/2002/acp-2-235-2002.html http://www.atmos-chem-phys.net/2/235/2002/acp-2-235-2002.pdf 235 247 2002-09-20 The adsorption of nitrogen oxides on crystalline ice T. Bartels B. Eichler P. Zimmermann H. W. Gäggeler M. Ammann Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland University of Berne, CH-3012 Bern, Switzerland The partitioning of nitrogen oxides between ice and air is of importance to the ozone budget in the upper troposphere. In the present study, adsorption of nitrogen oxides on ice was investigated at atmospheric pressure using a chromatographic technique with radioactively labelled nitrogen oxides at low concentrations. The measured retentions solely depended on molecular adsorption and were not influenced by dimerisation, formation of encapsulated hydrates on the ice surface, dissociation of the acids, nor by migration into a quasi-liquid layer or grain boundaries. Based on the chromatographic retention and the model of thermo-chromatography, the standard adsorption enthalpy of -20 kJ mol^-1 for NO, -22kJ mol^-1 for NO₂, -30kJ mol^-1 for peroxyacetyl nitrate, -32kJ mol^-1 for HON} and -44 kJ mol^-1 for HNO₃ was calculated. To perform those calculations within the model of thermo-chromatography, the standard adsorption entropy was calculated based on statistical thermodynamics. In this work, two different choices of standard states were applied, and consequently different values of the standard adsorption entropy, of either between -39 kJ mol^-1 and -45kJ mol^-1, or -164 kJ mol^-1 and -169 kJ mol^-1for each nitrogen oxide were derived. The standard adsorption enthalpy was identical for both standard adsorption entropies and thus shown to be independent of the choice of standard state. A brief outlook on environmental implications of our findings indicates that adsorption on ice might be an important removal process of HNO₃. In addition, it might be of some importance for HONO and peroxyacetyl nitrate and irrelevant for NO and NO₂.