A new laser induced fluorescence instrument for in-situ measurements of SO2 throughout the troposphere and lower stratosphere

Sulfur dioxide (SO2) is a ubiquitous naturally and anthropogenically emitted species, impacting air quality and climate in many ways. Measurements of SO2 are challenging in the stratosphere and remote troposphere due to very low mixing ratios (~10 ppt), and in polluted regions due to interfering species. New scientific understanding will be achievable with SO2 instrumentation capable of making accurate measurements in the low ppt range in the upper troposphere and lower stratosphere. We have developed a new laser-induced fluorescence based instrument for aircraft measurements of SO2 from the surface up to the lower stratosphere. The instrument uses a custom-built tunable fiber laser that produces > 1mW at 216.9 nm. Photons in the range 250-400 nm fluorescing from laser-excited SO2 are counted, yielding a 1-second detection limit (S:N=2) of < 20 ppt. The instrument has been compared on the ground to a commercial pulsed fluorescence instrument (TECO) and has been flown on the NASA WB-57F in the lower stratosphere. Here we will present details of the instrument, and results from the initial field deployment.