2015 News & Events

A new CSD instrument for measuring low concentrations of sulfur dioxide (SO₂) high in the atmosphere will take to the skies on October 19 onboard the NASA WB-57F high-altitude research aircraft, kicking off the Volcano-plume Investigation Readiness and Gas-phase and Aerosol Sulfur (VIRGAS) field experiment. In the five science flights of VIRGAS, the aircraft will range north and south of the base location in Houston to make measurements in the upper troposphere and lower stratosphere. In addition to the SO₂ instrument, other CSD instruments will measure water vapor and ozone, and instruments from NASA and the University of Miami will measure other sulfur-containing species and meteorological parameters. A research balloon will carry CSD's Printed Optical Particle Spectrometer (POPS) aloft in coordination with one of the WB-57F's flights, to get vertical profiles of the concentrations and sizes of atmospheric fine particles from the ground up into the lower stratosphere.

Why the focus on SO₂? Sulfur dioxide plays a principal role in connecting natural and anthropogenic emissions of sulfur species to major environmental issues such as acid rain, aerosol formation, air quality, and climate change. In the stratosphere, sulfur forms the ubiquitous sulfate aerosol layer, which affects climate through scattering and absorption of solar radiation. Various forms of sulfur in the atmosphere, such as dimethyl sulfide and carbonyl sulfide, are converted to SO₂ and then to sulfate in the sulfate aerosol layer, making SO₂ an especially critical species to measure. Key research issues include understanding how natural and human-caused emissions of sulfur species, for example from volcanoes and from fossil-fuel power sources, ultimately influence climate, air quality, and visibility.

Despite the importance of atmospheric sulfur and specifically SO₂ in so many arenas, routine SO₂ measurement techniques have not been up to the task because they lack the needed sensitivity in the remote atmosphere, particularly the stratosphere, and are plagued by interferences from other gases. CSD's new SO₂ instrument, developed by lead scientist Andrew Rollins and others at CSD, is expected to revolutionize the measurement of SO₂ because it remedies both of these problems. The new instrument is based on a novel custom laser system that uses an infrared laser source with fiber-optic amplification to generate intense UV light with a narrow wavelength range. This narrow UV light source is then used in a standard laser-induced fluorescence (LIF) detection cell to measure SO₂ with a detection limit 10 times smaller than previous aircraft SO₂ instruments and without interferences.

The VIRGAS experiment is a "mini-mission" to test what NASA and NOAA investigators hope will become a new standing capability for measuring SO₂, other gases, and particles in the plumes from large volcanic eruptions. The idea is that NASA, partnering with NOAA, would be able to deploy the WB-57F aircraft soon after future volcanic eruptions, giving scientists an unprecedented opportunity to observe the volcanic plume and understand the implications for climate and the atmosphere. It would also provide valuable insight into the implications of proposed mitigation strategies to counter climate warming by deliberate injections of sulfur into the atmosphere. Such injections, like explosive volcanic eruptions, would lead to an augmentation of the sulfate aerosol layer, but their effectiveness and other impacts on the atmosphere (such as damage to the ozone layer) are not certain.

The VIRGAS investigators hope that their measurements will help to characterize the stratospheric sulfate aerosol layer in this non-volcanic time period, and set the stage for new insights when Mother Nature's next volcanic eruption occurs.