A surrogate tracheobronchial (TB) system, capable of simulating the in vivo atmosphere (such as temperature and relative humidity) in a physiologically realistic manner, is reported here. This surrogate Toxicology Branch system is a tubular, multicomponent physical model where the average Reynolds number value for the airflow within each respective compartment, or section, equals the value within the corresponding bronchial airway generation of Weibel's Model A network. Mass-transport phenomenon (such as in vivo water flow through a TB wall and its membrane, and subsequent water evaporation into inhaled air) was simulated using this sytem. Detailed information regarding localized air temperature and water vapor concentration patterns for the steady flow rate of 13.5 l/min is reported in the work. The impact of the laryngeal simulator was studied, and average values of Nusselt and Sherwood numbers for each bronchial generation are reported. These values were lowest downstream from the laryngeal simulator. The in vitro temperature and water vapor concentration patterns and transfer coefficients can be used in a future quantitative analysis of the dynamic behavior and deposition rates of hygroscopic aerosol particles. (Copyright (c) 1989 Elsevier Science Publishing Co., Inc.)