Kinetic studies and the mechanism determination of ClONO2 uptake on polycrystalline NaCl were carried out using a coated-insert flow tube reactor combined with high-resolution, low-energy electron-impact mass spectrometer under the following conditions: p = 1-2 Torr, linear flow velocity nu = 3.5-75 m s(-1), T = 293 and 387 K, [ClONO2]) (0.5-25) x 1012 molecules cm(-3). The salt was deposited as a film from nonsaturated aqueous solution on the sliding rod. The temporal dependences of the uptake coefficient and the partial uptake coefficients leading to a formation of the prime Cl-2 and HOCl products were measured for different ClONO2 concentrations. These dependences are established to be described by gamma = gamma(0) exp(-t/tau) + gamma(s), gamma(-1)(0,s)) a(0,s) + b(0,s)[ClONO2]. In the framework of the proposed kinetic model, the data are explained and the main elementary kinetic parameters of the uptake are evaluated. The model is based on a combination of Langmuir adsorption, formation of surface complexes on initial active sites, Z(ch), followed by their unimolecular decomposition. Decomposition is proposed to proceed concurrently in two channels, one of which is a released surface site that conserves the properties of the initial site. In the other channel, the initial Z(ch) transforms into Z(ph) followed by steady-state uptake and reproduction of final Z(ph). The model gives an analytical expression for experimental parameters gamma(0), gamma(s), and tau in terms of elementary rate constants and the reactant volume concentration. The final objective of the proposed model is the extrapolation of gamma(0), gamma(s), and tau parameters to real tropospheric conditions.