This Standard provides the means to calculate atmospheric absorption losses of sound from any source, moving or stationary, for a wide range of meteorological conditions. The atmosphere is assumed to be still, homogeneous moist air of normal composition. Non-homogeneous atmospheres may be divided into horizontal layers within which homogeneous conditions may be assumed. Attenuation coefficients for pure-tone sounds are calculated by means of equations (or a table) over ranges of frequency, and the humidity, pressure, and temperature of the atmosphere. For sounds analyzed by fractional-octave- band filters (e.g., one-third-octave- band filters), alternative methods are provided in annexes to calculate the attenuation caused by atmospheric absorption from that specified for pure- tone sounds.