An ambient surface contamination sensor including a source for supplying gas, which is energized before it reaches the surface being sensed so that it is capable of transferring energy to the contaminants on the surface or vapor originating therefrom. The sensor then detects the optical emission from the gas passed over the surface within a selected wavelength band characteristic of the presence on the surface of the contaminant, and indicates the presence of the contaminant on the surface when such an emission is detected.