To gain quantitative understanding of the "stickiness" of a molecule on a given surface, we have developed a new diffusion tube method that allows us to measure changes in the surface residence times of unreactive as well as reactive adsorbants on solid substrates in real time. The experiment involves sending a pulse of molecules through a tube coated internally with a material of interest. The arrival time of the pulse is recorded using a mass spectrometer, which is mounted at the tube exit in a high vacuum chamber. Since the number of wall collisions under molecular flaw conditions is determined only by the tube geometry, the surface residence time can be calculated on a per collision basis. A Monte Carlo simulation, based on the assumption that the molecules are reflected upon collision with a cosine directional distribution, is used to model experimental results. In this study we have measured the surface residence times of two reactive, atmospherically relevant molecules, ClO2 and ClONO2, on sea-salt aerosol mimics (NaCl, KBr). We found an upper limit of 0.02 ms for the interaction of ClNO2 with KBr and a surface residence time of 0.7 +/- 0.2 ms for ClONO2 on NaCl at uptake coefficients of gamma = 0.0002 and 0.1, respectively.