Abstract
Abstract. 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 1084.5 nm to excite SO2 at 216.9 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 2 ppt at 10 s and an overall uncertainty determined primarily by instrument drifts of ±(16 % + 0.9 ppt).
Highlights
Sulfur dioxide (SO2) has long been recognized as an anthropogenic air pollutant and a precursor to aerosols throughout the atmosphere
In this work we describe the instrument and its initial performance in the UT– LS during the NASA Volcano-Plume Investigation Readiness and Gas-Phase and Aerosol Sulfur (VIRGAS) mission in October 2015
Two primary challenges distinguish this work from prior fiber-laser-based atmospheric Laser-induced fluorescence (LIF) measurements: (1) currently the required lasers are not commercially available, and (2) the scheme for generating 216.9 nm relies on μJ level pulse energies at 1084.5 nm, which has a significantly lower Yb3+ emission cross section than the 1059 nm used for CH2O, which makes it harder to achieve the required total gain
Summary
Sulfur dioxide (SO2) has long been recognized as an anthropogenic air pollutant and a precursor to aerosols throughout the atmosphere. There are significant uncertainties in the relationship between aerosol radiative forcing and the upward flux of sulfur mass to the stratosphere These uncertainties affect confidence in proposed climate intervention measures that would seek to increase Earth’s albedo by injecting SO2 into the stratosphere (McNutt et al, 2015). Photons from a xenon lamp (∼ 205–220 nm) are used to electronically excite SO2, resulting in measurable red-shifted fluorescence This technique suffers limited precision and significant interferences from other pollutants such as nitric oxide and aromatic compounds due to the broadband nature of the excitation source. LIF was first reported as a technique for measuring atmospheric SO2 by Bradshaw et al (1982) They mixed the 1064 nm output of a Nd+YAG laser with the frequency-doubled output of a dye laser at 10 Hz to achieve 10 mW of tunable light at 222.2 nm. In this work we describe the instrument and its initial performance in the UT– LS during the NASA Volcano-Plume Investigation Readiness and Gas-Phase and Aerosol Sulfur (VIRGAS) mission in October 2015
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