The heterogeneous uptake of N 2 O 5 on mineral dust particles may play an important role in the removal of nitrogen oxides from the atmosphere. However, the reaction of N 2 O 5 with the mineral particles is not well understood. The reaction of N 2 O 5 with two Si(OH) 4 monomers is explored using theoretical methods. This study represents a first step towards understanding the interaction of N 2 O 5 with the hydroxyl groups of silica particles. Energies are calculated using MP2 single point calculations on the B3LYP optimized geometries and including B3LYP thermodynamic corrections. Four mechanisms are considered for the formation of two HNO 3 and one H 6 Si 2 O 7 . The rate limiting activation barrier of the most favorable path is found to be 12.5 kcal mol À1 . This reaction appears to be more favorable than the hydrolysis of N 2 O 5 with one water molecule. These results are in agreement with experimental observations, which show that N 2 O 5 reacts with OH groups of Saharan dust to form nitrate.