Detection of Sulfur Dioxide by Broadband Cavity-Enhanced Absorption Spectroscopy (BBCEAS)

TL;DR

This paper introduces a BBCEAS instrument capable of detecting sulfur dioxide at very low concentrations with high accuracy, using a UV LED and high-reflectivity mirrors, suitable for atmospheric monitoring.

Contribution

The study presents a novel BBCEAS setup for SO₂ detection with improved sensitivity and no interference, validated against fluorescence standards.

Findings

Detection limit of 0.75 ppbv for SO₂

High correlation (R²=0.9998) with fluorescence measurements

No interference observed in ambient measurements

Abstract

Sulfur dioxide ($\mathrm{SO}_2$) is an important precursor for the formation of atmospheric sulfate aerosol and acid rain. We present an instrument using Broadband Cavity-Enhanced Absorption Spectroscopy (BBCEAS) for the measurement of $\mathrm{SO}_2$ with a minimum limit of detection of 0.75 ppbv (3-$\sigma$) using the spectral range 305.5--312 nm and an averaging time of 5 min. The instrument consists of high-reflectivity mirrors (0.9985 at 310 nm) and a deep UV light source (Light Emitting Diode). The effective absorption path length of the instrument is 610 m with a 0.966 m base length. Published reference absorption cross sections were used to fit and retrieve the $\mathrm{SO}_2$ concentrations and were compared to fluorescence standard measurements for $\mathrm{SO}_2$. The comparison was well correlated ($R^2 = 0.9998$) with a correlation slope of 1.04. Interferences for fluorescence measurements were tested, and the BBCEAS showed no interference, while ambient measurements responded similarly to standard measurement techniques.