This is the version 3 Atmospheric Trace Molecule Spectroscopy (ATMOS) Level 2 product containing trace gases on a vertical potential temperature (theta) grid with data stored in an ASCII table using a FORTRAN friendly fixed field format. ATMOS is an infrared spectrometer (a Fourier transform interferometer) designed to derive vertical concentrations of various trace gases in the atmosphere, particularly the ozone depleting chlorine and fluorine based molecules. Measured species include: H2O, CO2, O3, N2O, CO, CH4, NO and NO2 (both diurnally and not diurnally corrected), HNO3, HF, HCl, OCS, H2CO, HOCl, H2O2, HO2NO2, N2O5, ClONO2, HCN, CH3F, CH3Cl, CF4, CCl2F2, CCl3F, CCl4, COF2, C2H6, C2H2, N2, CHF2Cl, HCOOH, HDO, SF6 and CH3D reported at 53 levels from 280 to 3950 K. Data files also include time, geolocation and other information.The data were collected during four space shuttle missions: STS-51B/Spacelab-3 (April 30 to May 1, 1985), STS-45/ATLAS-1 (March 25 to April 2, 1992), STS-55/ATLAS-2 (April 8 to 16, 1993), and STS-66/ATLAS-3 (November 3 to 12, 1994). Data are written to separate files grouped by mission (sl3, at1, at2 or at3), and occultation type (sunrise or sunset) and number.A similar product (ATMOSL2TT) exists that contains these same data in a spreadsheet friendly tab delimited format.