Gas membranes can be used to rapidly remove volatile solutes like hydrogen sulfide and sulfur dioxide from dilute aqueous solutions. The gas membranes are supported by microporous hydrophobic hollow fibers. The aqueous feed containing the volatile component flows down the fiber lumen, and an aqueous stripping solution bathes the outside fiber surface. Thus the membrane consists of gas trapped in the hydrophobic pores. The fluxes across these membranes, which can be much faster than those across polymer films, are consistent with a nonlinear mechanism which includes solute ionization.