Fig. 1. Simulated frequency response of the photoacoustic cell at different pressures

Fig. 2. Schematic of the structure of the photoacoustic SO₂ sensor

Fig. 3. Schematic of the photoacoustic SO₂ sensing system

Fig. 4. Amplitude-frequency response of photoacoustic SO₂ sensor

Fig. 5. Frequency response of the signal-to-noise ratio of the photoacoustic SO₂ sensor

Fig. 6. Gas pressure characteristics of amplitude-frequency response

Fig. 7. Effect of gas pressure on background signal and noise

Fig. 8. Effect of gas pressure on detection limit

Fig. 9. Measured noise level andAllan-Werle analysis of photoacoustic SO₂ sensor at 0.4 MPa（illustration）