Disclosed are apparatus for delivery of a gas, e.g., carbon dioxide and/or chlorine dioxide, and methods of its use and manufacture. The apparatus includes a sachet constructed in part with a hydrophobic material. The sachet contains one or more reactants that generate a gas in the presence of an initiating agent, e.g., water. The apparatus can also include a barrier layer and/or a rigid frame. In another embodiment, the apparatus is combined with a reservoir that can be used to deliver a gas to the reservoir and, optionally, a conduit. In another embodiment, the apparatus is incorporated into a fluid dispersion system that includes a dispersion apparatus, e.g., a humidifier.