An early warning sulfur detection system for detecting the presence of corrosive gases, especially elemental sulfur (S8), in air employs a substrate that includes a polymer-bound phosphine compound having sulfur-getting functionality. The phosphine compound in the polymer reacts with any airborne elemental sulfur. This reaction is accompanied by a decrease in the fluorescence intensity (If) of the substrate. The If of the substrate is monitored in real time by a spectrofluorometer to detect a change in fluorescence intensity (ΔIf). In an embodiment sited in a data center, an alarm is triggered if the ΔIf is above a predetermined threshold, thereby providing a real-time, early warning to IT professionals that corrective action is required to protect metal conductors from corrosion. Preferably, the phosphine compound in the polymer does not react with other components in the air (e.g., carbon dioxide).