Dynamic detection of ppb-level SO2 based on a differential photoacoustic cell coupled with UV-LED

We design a photoacoustic (PA) SO 2 sensor based on the coupling of a differential photoacoustic cell (DPAC) and cost-effective UV-LED, which realized the dynamic monitoring of SO 2 gas at the ppb level. Aiming at the limitation of UV-LED divergence, a light source combination module with high condensing efficiency was devised based on a lens through theoretical derivation and experimental analysis. The PA signal with the optimum matching of the lens was 20-times larger than the direct coupling of the UV-LED. Due to the excellent beam collimation effect of the lens assembly, the background interference was only 1 ppm. In addition, the DPAC gathered the merits of doubling the PA signal and reducing the flow noise interference. The analysis of Allan–Werle deviation showed that the detection limit of SO 2 was 1.3 ppb with the averaging time of 100 s.