A laser-induced fluorescence instrument for aircraft measurements of sulfur dioxide in the upper troposphere and lower stratosphere Atmospheric Measurement Techniques

This work describes the development and testing of a new instrument for in situ measurements of sulfur dioxide (SO2) on airborne platforms in the upper troposphere and lower stratosphere (UT-LS). The instrument is based on the laser-induced fluorescence technique and uses the fifth harmonic of a tunable fiber-amplified semiconductor diode laser system at 1084.5aEuro-nm to excite SO2 at 216.9aEuro-nm. Sensitivity and background checks are achieved in flight by additions of SO2 calibration gas and zero air, respectively. Aircraft demonstration was performed during the NASA Volcano-Plume Investigation Readiness and Gas-Phase and Aerosol Sulfur (VIRGAS) experiment, which was a series of flights using the NASA WB-57F during October 2015 based at Ellington Field and Harlingen, Texas. During these flights, the instrument successfully measured SO2 in the UT-LS at background (non-volcanic) conditions with a precision of 2aEuro-ppt at 10aEuro-s and an overall uncertainty determined primarily by instrument drifts of +/-(16aEuro-%aEuro-+aEuro-0.9aEuro-ppt).