Sound speed in air: Past and present

The calculation of a new value for the sound speed (C0 = 331 ⋅ 29 ms−1) in standard dry air at 0°C and at a barometric pressure of 101.325 kPa is presented. The maximum uncertainty in this sound speed C0 is estimated to be approximately 200 ppm. The theory of the above calculation is based on the equation of state, and with the knowledge of γ/M which is derived from published theoretical and experimental thermodynamic data on the constituents of the standard atmosphere [G. S. K. Wong and T. F. W. Embleton, J. Acoust. Soc. Am. 76, 555–559 (1984)], and M is the molar mass. Investigations which led to the general acceptance of the previous sound speed are examined, and there is strong evidence that enables one to conclude that the maximum possible uncertainties in previous sound-speed assessments are sufficient to encompass the above new sound speed. The effects of carbon dioxide on sound speed are discussed.