The heterogeneous reactions of NO3 on NaCl and KBr salt were studied at room temperature using a Knudsen reactor equipped with dual detection, namely Laser induced fluorescence (LIF) and mass spectrometry (MS). The uptake coefficients of NO3 were found to be &ggr;=(4.9¿3)⋅10-2 onto NaCl and &ggr;=0.16¿0.08 onto KBr. In the case of NaCl, HCl was the sole product observed. However, there is indirect evidence that Cl atoms are the primary products. In the case of KBr we observed Br2 and Br to be the products of reaction. A first estimation of the atmospheric relevance of these reactions indicate that under certain conditions the heterogeneous loss of NO3 on seasalt aerosols may compete with removal by homogeneous gas phase reactions. ¿ 1997 American Geophysical Union