The speed of sound in humid air is a thermodynamic property of fundamental importance in many scientific and technological fields, including aerodynamics, acoustic thermometry, or atmospheric physics.
The most comprehensive theoretical model previously available in the literature dates back to 2002 and allows the speed of sound in air to be calculated from environmental parameters and acoustic frequency; however, it is limited to an uncertainty of 0.1%.
A new study from the National Metrology Institute of Italy INRiM, published in the Journal of Physical and Chemical Reference Data (AIP Publishing), significantly improves the accuracy of this model. The work integrates the most up-to-date and accurate thermodynamic information for dry air, water vapour, and their interactions.
Thanks to this approach, the uncertainty has been reduced by more than one order of magnitude, reaching values as low as 25 parts per million (ppm) under ordinary environmental conditions.
The model was validated through comparison with two independent techniques for measuring the speed of sound in air, showing excellent agreement between experimental results and theoretical predictions within their respective uncertainties.
In line with the principles of open science, the software implementing the model calculations is freely available for download at the following link.
The article was selected by the Publisher as a Featured Article and was also presented on Scilight as one of the most relevant articles published in AIP journals in 2025.