Free energy profiles associated with moving atmospheric gases or radicals 
across the air/water interface were calculated as potentials of mean force 
by classical molecular dynamics simulations. With the employed force field 
the experimental hydration free energies are satisfactorily reproduced. 
The main finding is that both hydrophobic gases (nitrogen, oxygen, and ozone), 
as well as hydrophilic species (hydroxyl radical, hydroperoxy radical, 
or hydrogen peroxide) have a free energy minimum at the air/water interface. 
As a consequence, it is inferred that atmospheric gases, with the exception 
of water vapor, exhibit enhanced concentrations at surfaces of aqueous aerosols. 
This has important implications for understanding heterogeneous chemical 
processes in the troposphere.