The infrared spectral measurements made by the Nimbus 4 infrared interferometer spectrometer (Iris) for a period of about 10 months are used to study the surface emissivity properties over the globe. It is found that the surface emissivity at 9μm (e9), as measured by Iris with a circular field of view of about 100-km diameter, is significantly less than unity over arid and semiarid land areas. The spectral features in the 8- to 12-μm window, observed over these lands, reveal emissivity characteristics essentially due to quartz (SiO2). It is found that these emissivity features are significantly weakened by the presence of clay, clay horizons, or pedogenic horizons in the soil. Low emissivity (e9~0.7) is observed over sandy or sandy loam areas (psamments) with no clay or pedogenic horizons.