Compositions for CO.sub.2 detector solutions and rapid-response reversible dry surface CO.sub.2 detectors made from them are disclosed. The CO.sub.2 detector solutions generally comprise a poly(oxyethylene) based compound, a pH sensitive indicator dye, an organic solvent, a cationic phase transfer agent and an anionic base. However, minimally these detector solutions comprise a poly(oxyethylene) based compound, a pH sensitive indicating dye, an organic solvent and a base. The solutions were embedded onto a solid support made of polyethersulfone filter material in order to form rapid-response reversible dry surface CO.sub.2 detectors. Rapid-response reversible dry surface CO.sub.2 detectors are produced which function at rates in excess of 180 one-way color changes/minute when exposed to alternating 0% and 5% CO.sub.2 concentrations. A preferred embodiment using cationic methyltricaprylylammonium in conjunction with the phenoxide anion is substantially humidity resistant.
