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

Abstract

We design a photoacoustic (PA) SO2 sensor based on the coupling of a differential photoacoustic cell (DPAC) and cost-effective UV-LED, which realized the dynamic monitoring of SO2 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 SO2 was 1.3 ppb with the averaging time of 100 s.