The hygroscopicity of the aerosols could be utilized to enhance the delivery efficiency of the drug aerosols for pulmonary diseases. In a simple mouth-throat airway model, the heat and mass transfer of the airway boundary, i.e., convection over the mucus layer, evaporation heat of the water vapor evaporated from the mucus layer and the conduction in the mucus-tissue region, have been found to have notable impacts on the transport and deposition of hygroscopic aerosols (Chen et al., 2018). The effect of this coupled heat and mass transfer on the hygroscopic aerosol transport is yet unknown in the deeper lung region in light of the increases of the airway temperature and humidity. This numerical study investigates the transport and deposition of the hygroscopic aerosols in a G3-G6 lung airway under three conditions: (i) constant temperature at 37 degrees C and constant relative humidity (RH) at 0% in the whole airway, i.e., neglecting hygroscopicity; (ii) more realistic boundary including the mass and heat transfer at the airway boundary; (iii) constant temperature at 37 degrees C and constant RH at 99.5% in the whole airway. Besides the temperature and RH distributions of the airway, the deposition fractions and deposition patterns of the hygroscopic aerosols as well as the distributions of the escaped aerosols are compared. As the most important outcome, the results show that using the heat and mass transfer of the airway boundary can better predict the aerosol hygroscopic growth and thereby more accurately estimate the deposition fraction of the hygroscopic aerosol. Thus, for the design of a high efficiency pulmonary drug delivery system, including the device and the hygroscopic drug aerosol, on a patient-specific level in future, the heat and mass transfer of the airway boundary should be considered. (C) 2019 Published by Elsevier Ltd.