The heterogeneous reaction of NO2 on NaCl particles has been investigated with the new sample preparation and the mode of gas-solid free diffusion. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) is used to characterize the adsorbed products in situ, combined with Ion Chromatographic (IC), X-ray Photoelectron Spectroscopy (XPS) and Scan Electron Microscopy (SEM). Our results indicate that the reaction is not limited to the surface of the NaCl particles, but penetrated into the upper layers. Surface reactive sites determine the reaction. Kinetic measurements show that nitrate formation on sodium chloride is second order in NO2 concentration and reactive uptake coefficient is (1.54 ± 0.70) × 10-5.