ESDU 78002 provides tables of values for the rate of atmospheric attenuation at one-third octave band centre frequencies from 50 Hz to 100 kHz due to gaseous absorption in a still homogeneous atmosphere. Each table applies to a value of relative pressure (0.8@ 0.9@ 1 or 1.1) and a range of relative humidity from 10 to 95 per cent and of temperature from 270 to 310 K. The mechanisms of atmospheric attenuation are discussed. The theoretical approach used to calculate the data is outlined. A Fortran program@ ESDUpac A7802@ implementing it is provided on disc in the software volume both uncompiled and compiled in ESDUview@ a user-friendly shell that prompts on-screen for input data. The output may be at one-third octave band centre frequencies or at any set of frequencies chosen by the user up to 50. ESDU 78003 gives a method of accounting for variations in atmospheric conditions over the propagation path and also shows how the band attenuation coefficient can be calculated from the discrete frequency data.