In this study, the quality factor and cell constant vs acoustic resonator sizes in the first radial and longitudinal modes were calculated using our homemade simulation. Based on these simulations a photoacoustic (PA) spectroscopy system was designed, optimized, and finally fabricated as a highsensitivity gas sensor. The subsequent experiments have been done to online monitoring of the trichloromethane (CHCl3) vapors trace. The sensitivity of system for detection of CHCl3 vapors was measured 488 ppb. Corresponding PA signal for different concentrations of CHCl3 vapors is determined in the presence of N2, synthetic air, He, and Ar in various gas environments. It is shown that the effect of buffer gas and the relevant pressures are substantiated to achieve the minimum detectable concentration. In other words, using heavier gases at the same experimental conditions lead to detection of the lower concentrations. When the buffer gas of system was He, the lowest PA signal was recorded. This faint signal of He is due to vibrational-translational processes of He, thermodynamic and acoustic properties of system such as cell constant, quality factor, speed of sound, thermal diffusion, thermal boundary layer, and viscous boundary layer for He. These properties for various buffer gases were calculated and discussed.
