Atmospheric'spectroscopy, employing the sun as a source, has been routinely used for a number of years as a means for identification and quantitative measurements of atmospheric species. Recent improvements in Pb-salt semiconductor laser technology when combined with infrared heterodyne technology provide the capability of obtaining solar spectra with sub-Doppler spectral resolution. In this paper we discuss ultrahigh resolution (0.007 cm-1) atmospheric solar absorption spectra that have been obtained from a tunable infrared heterodyne radiometer. The radiometer was developed for ground based observations in the 8 to 12µm region, and tunability is achieved through the use of Pb-salt semiconductor laser local oscillators (L0). Spectra have been obtained in a piece-wise fashion from 9.1 to 11.1 um using laser emission modes that exhibit characteristics suitable for LO operation. Spectra showing absorption features of HNO3, 03, CO2, and H2O are presented along with comparisons of experimental and synthetic spectra calculated using a line-by-line atmospheric transmission model.