Molecular dynamics simulations with many-body interactions were carried out to systematically study the effect of anion type, tetrafluoroborate [BF4] or hexafluorophosphate [PF6], paired with the cation 1-butyl-3-methylimidazolium [bmim], on the interfacial absorption of gases in room temperature ionic liquids (RTILs). The potentials of mean force (PMF) of CO2 and H2O at 350 K were calculated across the air-liquid interfaces of [bmim][BF4] and [bmim][PF6]. We found that the PMFs for H2O exhibited no interfacial minima at both interfaces, while the corresponding PMFs for CO2 had significant free energy minima there. However, the PMFs for H2O showed a much higher interfacial free energy than in the bulk for [bmim][BF4], but only a slightly higher interfacial free energy for [bmim][PF6] than in bulk. The reason for this was due to the more hydrophilic nature of the [BF4] anion, and the fact that [BF4] was found to have little propensity for the interface. Our results show that H2O is much more likely to be found at the air-[bmim][PF6] interface than at the air-[bmim][BF4] interface. The free energies of solvation were found to be more negative for [bmim] [BF4] than [bmim][PF6] for water and similar for CO2. This observation is consistent with experimental Henry's law coefficients. Our results show that anion type, in addition to affecting the free energy of solvation into RTILs, should also significantly influence the uptake mechanism.