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A photoacoustic sensor using a laser diode emitting near 1573 nm in combination with a dual-microphone resonant photoacoustic cell has been developed for carbon dioxide trace gas analysis at atmospheric pressure. Wavelength-modulation scheme and 1f detection for CO2 concentration measurements in Ar are demonstrated. The noise equivalent absorption sensitivity of NEAS(1σ) = 1.01×10–8 Wcm–1/Hz1/2, corresponding to a detection limit of 30 parts in 106 by volume (ppmv) for a 100 s integration time and 4.5 mW average laser power. The photoacoustic response of CO2 dependence on the buffer gases with different mixture ratio of Ar and N2 was investigated. Finally, the possibility to make use of the sensor for measurements of ambient CO2 is also presented.