The effects of the concentrations of biomass, mixed salts, total carbohydrates, and proteins on atmospheric CO2 transfer in a bubble column photobioreactor during the photoautotrophic culture of Chlamydomonas reinhardtii were studied. Microalgae cultures were carried out in saline media at three superficial gas velocities and two initial salt concentrations in terms of ionic strength. The influence of the gas superficial velocity and the instantaneous concentrations on both the liquid side mass-transfer coefficient (k(L)) and the specific interfacial area (a) were analyzed using a multifactor analysis of variance. k(L) decreased as the gas velocity increased, but a increased; the reduction of k(L) was due to transition behaviors between those expected for isolated bubbles and bubble swarms. As the biomass concentration increased, a decreased and k(L) increased. In addition, at higher initial ionic strength, a was larger. The mass transfer was independent of the concentrations of total carbohydrates and proteins.