ppb-Level SO₂ Photoacoustic Sensors with a Suppressed Absorption-Desorption Effect by Using a 7.41 μm External-Cavity...

Area of Science:

• Environmental Science
• Analytical Chemistry
• Spectroscopy

Background:

• Sulfur dioxide (SO2) is a major air pollutant with significant environmental and health impacts.
• Accurate and sensitive detection of SO2 is crucial for environmental monitoring and industrial safety.
• Existing detection methods may have limitations in sensitivity, response time, or portability.

Purpose of the Study:

• To develop a highly sensitive photoacoustic sensor system for detecting ppb-level sulfur dioxide (SO2).
• To optimize the sensor system using a quantum cascade laser (QCL) and a custom differential photoacoustic cell (PAC).
• To investigate and mitigate SO2 adsorption-desorption effects within the sensor cell.

Main Methods:

• Utilized a continuous-wave, high-power quantum cascade laser (QCL) tuned to 7.41 μm, targeting the strongest SO2 absorption line.
• Designed and employed a custom differential photoacoustic cell (PAC) with two identical resonators, enabling gas flow rates up to 1200 sccm.
• Developed a qualitative theoretical model to understand SO2 dynamic adsorption and desorption processes within the PAC.

Main Results:

• Achieved a 1σ detection limit of 2.45 ppb for sulfur dioxide.
• Attained a normalized noise equivalent absorption value of 3.32 × 10⁻⁹ cm⁻¹ W/Hz¹/².
• Successfully suppressed the absorption-desorption effect, enhancing sensor performance.

Conclusions:

• The developed photoacoustic sensor system demonstrates high sensitivity and accuracy for ppb-level SO2 detection.
• The use of a QCL and a custom PAC design, coupled with mitigation of adsorption effects, provides a robust platform for SO2 monitoring.
• This technology offers potential for improved environmental monitoring and industrial gas sensing applications.