We investigated the signature phenomenology of long-wave infrared (LWIR) reflectance of contaminated surfaces using a quantum-cascade laser (QCL) that runes from n = 9.1 to 9.8 um and a HgCdTe focal-plane-array (FPA) with custom read-out integrated circuit (ROIC). A liquid chemical, diethyl phthalate (DEP), was applied to a variety of substrates such as diffusely reflecting gold, concrete, asphalt, and sand. Multispectral image-cubes of the scattered radiation were generated over 81 wavelengths in steps of 1 cm-1 at standoff distances ranging from 0.1 to 5 meters. For idealized substrates such as diffusely reflecting gold, the experimentally measured signatures are in good agreement with theoretical calculations. Clear signatures were also obtained for contaminated concrete, asphalt, and sand. These measurements demonstrate the potential of this technique for detecting and classifying chemicals on native outdoor surfaces.