## 1 Introduction
The European Norm EN 12354-6 [11] provides formulas for calculation of the reverberation time in a room from the total equivalent absorption area including the air absorption. A table is provided with energy attenuation coefficients in air in octave bands for selected examples of temperature and humidity. Below 1 kHz, these coefficients are the pure-tone attenuation coefficients of the center frequency of the octave band. For the 1 kHz to the 8 kHz octave bands, the coefficients are the pure-tone attenuation coefficients of the center frequency of the lower one-third octave within the octave band. This is assumed to handle the spectral change within the octave band during the sound propagation. Extensive experiments in a 175 m\({}^{3}\) room with changeable temperature and relative humidity (RH) were reported by [PERSON] et al. [12]. The temperature varied in the range of 12 \({}^{\circ}\)C to 38 \({}^{\circ}\)C and the RH in the range of 15% to 80%. The average reverberation time of the room was 1.7 s. The octave band reverberation time \(T_{20}\) was derived in ten octave bands with center frequencies from 31.5 Hz to 16 kHz. The statistical correlation between the measured reverberation time and the RH was analyzed. Good correlation was found for frequencies 1 kHz and 2 kHz when fitting to the pure-tone attenuation of the center frequency of the octave band. For frequencies of 4 kHz and higher, a good correlation was found when fitting to the pure-tone attenuation of the lower limiting frequency of the octave band. It is noted that the limiting frequency is called the edge frequency in [12]. Using the attenuation of the lower edge frequency is called the edge frequency method, and it is suggested by the authors to overcome the problem of non-linear attenuation in octave bands. A later study by [PERSON] et al. [13] deals with calculations of reverberation time in octave bands and the investigation of different methods, including the edge frequency method, to estimate the effect of air absorption. As a reference, calculations of decay curves with the summation of 96 frequencies within each octave band are utilized. This summation method is similar to that used by [PERSON] and [PERSON] [6]. For high frequencies and reverberant spaces, it is recommended that air absorption in octave bands is calculated using the summation method, whereas for one-third octave bands, it is sufficiently accurate to use the pure-tone attenuation at the center frequency. It is also found that the reverberation time averaged over three one-third octave bands is not equal to the reverberation time derived from the full octave band containing those one-third octave bands. Finally, the study investigates the problem of measurement in acoustic scale models and how to adjust for excessive air absorption at very high frequencies. Experimental data of room acoustical parameters measured under different thermogravimetric conditions were analyzed statistically by [PERSON] [14] and [PERSON] et al. [15]. The temperature varied between 27 and 32 \({}^{\circ}\)C and the relative humidity between 38 and 55% RH. The air velocity varied between 0 and 0.56 m/s due to fans in operation. It should be noted that the absolute humidity of the air was almost constant, and, thus, the relative humidity was directly linked to the temperature. This implies that the actual variation in air attenuation was very limited. The experimental results led the authors to claim that sound absorption due to air attenuation is not sensitive to variations in humidity. It was found that the room acoustic parameters most influenced by changes in temperature and humidity were \(C_{80}\) and \(T_{30}\), while the least influenced were \(D_{50}\) and EDT. However, these findings are most likely due to variations in the speed of sound and not to variations in the air attenuation.